vitamin

Vision Health A step-by-step "how-to" instruction.

More about Vitamins: Purpose Precautions Preparation Aftercare Risks Resources

Definition

Vitamins are organic components in food that are needed in very small amounts for growth and for maintaining good health. The vitamins include vitamin D, vitamin E, vitamin A, and vitamin K, or the fat-soluble vitamins, and folate (folic acid), vitamin B₁₂, biotin, vitamin B₆, niacin, thiamin, riboflavin, pantothenic acid, and vitamin C (ascorbic acid), or the water-soluble vitamins. Vitamins are required in the diet in only tiny amounts, in contrast to the energy components of the diet. The energy components of the diet are sugars, starches, fats, and oils, and these occur in relatively large amounts in the diet.

Most of the vitamins are closely associated with a corresponding vitamin deficiency disease. Vitamin D deficiency causes rickets, a disease of the bones. Vitamin E deficiency occurs only very rarely, and causes nerve damage. Vitamin A deficiency is common throughout the poorer parts of the world, and causes night blindness. Severe vitamin A deficiency can result in xerophthalamia, a disease which, if left untreated, results in total blindness. Vitamin K deficiency results in spontaneous bleeding. Mild or moderate folate deficiency is common throughout the world, and can result from the failure to eat green, leafy vegetables or fruits and fruit juices. Folate deficiency causes megaloblastic anemia, which is characterized by the presence of large abnormal cells called megaloblasts in the circulating blood. The symptoms of megaloblastic anemia are tiredness and weakness. Vitamin B₁₂ deficiency occurs with

the failure to consume meat, milk or other dairy products. Vitamin B₁₂ deficiency causes megaloblastic anemia and, if severe enough, can result in irreversible nerve damage. Niacin deficiency results in pellagra. Pellagra involves skin rashes and scabs, diarrhea, and mental depression. Thiamin deficiency results in beriberi, a disease resulting in atrophy, weakness of the legs, nerve damage, and heart failure. Vitamin C deficiency results in scurvy, a disease that involves bleeding. Specific diseases uniquely associated with deficiencies in vitamin B₆, riboflavin, or pantothenic acid have not been found in the humans, though persons who have been starving, or consuming poor diets for several months, might be expected to be deficient in most of the nutrients, including vitamin B₆, riboflavin, and pantothenic acid.

Some of the vitamins serve only one function in the body, while other vitamins serve a variety of unrelated functions. Hence, some vitamin deficiencies tend to result in one type of defect, while other deficiencies result in a variety of problems.

Description

Vitamin treatment is usually done in three ways: by replacing a poor diet with one that supplies the recommended dietary allowance, by consuming oral supplements, or by injections. Injections are useful for persons with diseases that prevent absorption of fat-soluble vitamins. Oral vitamin supplements are especially useful for persons who otherwise cannot or will not consume food that is a good vitamin source, such as meat, milk or other dairy products. For example, a vegetarian who will not consume meat may be encouraged to consume oral supplements of vitamin B₁₂.

Treatment of genetic diseases which impair the absorption or utilization of specific vitamins may require megadoses of the vitamin throughout one's lifetime. Megadose means a level of about 10-1,000 times greater than the RDA. Pernicious anemia, homocystinuria, and biotinidase deficiency are three examples of genetic diseases which are treated with megadoses of vitamins.

— Tom Brody, PhD

Any of various fat-soluble or water-soluble organic substances essential in minute amounts for normal growth and activity of the body and obtained naturally from plant and animal foods.

[Alteration of vitamine : Latin vīta, life + AMINE (so called because they were originally thought to be amines).]

Key Terms: Antioxidant, Cancer, Free radicals, Malignant.

Definition

Vitamins are compounds that are essential in small amounts for proper body function and growth. Vitamins are either fat soluble: A, D, E, and K; or water soluble: vitamin B and C. The B vitamins include vitamins B₁(thiamine), B₂ (riboflavin), and B₆ (pyridoxine), pantothenic acid, niacin, biotin, folic acid (folate), and vitamin B₁₂ (cobalamin). Vitamins also may be referred to as micronutrients.

Description

A guide to the amount an average person needs each day to remain healthy has been determined for each vitamin. In the United States, this guide is called the recommended daily allowance (RDA). Consuming too little of certain vitamins may lead to a nutrient deficiency. Consuming too much of certain vitamins may lead to nutrient toxicity.

Consumption of a wide variety of foods that have adequate vitamins and minerals is the basis of a healthy diet. Good nutrition may assist in the prevention of cancer or may help cancer patients to feel better and fight infection during treatments. Obtaining nutrients through food remains the best method for obtaining vitamins, however, requirements may be higher because of the tumor or cancer therapy. Therefore, supplements may be necessary.

The following vitamins are important in a healthy diet and also may assist in cancer prevention. Their role in maintaining health and the best food sources are listed below.

Vitamin A (retinal, carotene)

• role in growth and repair of body tissues
• important in night vision
• immune function
• Best sources: eggs, dark green and yellow fruits and vegetables, low-fat dairy products, liver

Vitamin B6 (pyridoxine)

• role in formation of antibodies
• important in carbohydrate and protein metabolism
• red blood cells
• nerve function
• Best sources: lean meat, fish, poultry, whole grains, and potatoes

Folic acid (folate)

• assists in red blood cell formation
• important in protein metabolism
• growth and cell division
• Best sources: green leafy vegetables, poultry, dried beans, fortified cereals, nuts, and oranges

Vitamin C (ascorbic acid)

• resistance to infection
• important in collagen maintenance
• contributes to wound healing
• strengthens blood vessels
• assists in maintaining healthy gums
• Best sources: citrus fruits, tomatoes, melons, broccoli, green and red peppers, and berries

Vitamin E (tocopherol)

• may assist in immune function
• important in preventing oxidation of red blood cells and cell membranes
• Best sources: vegetable oils, wheat germ, nuts, dark green vegetables, beans, and whole grains

Purpose

Specific nutrients have been linked to prevention of several cancers of the colon, breast, prostate, stomach, and other types of tumors. A high intake of fruits and vegetables as well as fiber appears particularly protective, while a diet high in fat has been implicated as a cancer risk.

Vitamins Important for Cancer Prevention

Antioxidant vitamins are believed to protect the body from harmful free radicals that can contribute to diseases such as cancer. Antioxidant vitamins include vitamin A, C, and E. However, doses too high may increase oxidative stress and therefore may increase cancer risk.

A diet rich in fruits and vegetables (containing B6, folate, and niacin) appears to protect against stomach cancer and in particular, intestinal cancer.

One study reported that cruciferous vegetables, especially broccoli, brussel sprouts, cauliflower, and cabbage were associated with a decreased risk of prostate cancer. Other foods, such as carrots, beans, and cooked tomatoes, also were associated with a lower risk.

A component of Vitamin E, tocotrienol, has been linked to a decreased risk of breast cancer in lab animals. Tocotrienol has been shown to readily kill tumor cells grown in culture. Tocotrienol is not the same type of substance found in generic Vitamin E supplements, but is plentiful in palm oil. Palm oil is difficult to obtain in the Western world, but lower concentrations of tocotrienol are found in rice bran oil and wheat bran oil. In 2004, research showed that the nutrient calcium and vitamin D worked together, not separately, to lower risk of colorectal cancer.

Researchers state that no single nutrient is the answer, but that the effects are cumulative and depend on eating a variety of fruits and vegetables. Because there are many more nutrients available in foods such as fruits and vegetables than in vitamin supplements, food is the best source for acquiring needed vitamins and minerals.

Special Concerns

For many years, debate has continued regarding taking vitamin supplements to prevent cancer. In 2004, the U.S. Preventive Services Task Force concluded that the evidence is inadequate to recommend supplementation of vitamins A, C, or E, multivitamins with folic acid, or antioxidant combinations to decrease the risk of cancer. Beta-carotene supplements should not be used in patients with no symptoms because there is no evidence of risk reduction and some evidence that these supplements may cause harm to some patients.

There are concerns regarding antioxidant levels during chemotherapy and radiation therapy. Researchers report large amounts of Vitamin C are consumed by cancerous tumors during chemotherapy in studies with mice. Vitamin C is an antioxidant that consumes free radicals and is thought to perhaps interfere with the process of killing cancer cells during chemotherapy or radiation therapy. Cancer patients undergoing chemotherapy are advised against taking large amounts of Vitamin C. Another research study also has warned cancer patients about vitamin A and vitamin E during chemotherapy because it has demonstrated a protective effect on cancer cells in mice. These antioxidants may protect not only the normal cells from being destroyed, but also may protect dangerous cancer cells from being destroyed during cancer treatment. The researchers suggest an antioxidant-depleted diet may be prudent during cancer therapy.

Smokers are advised not to consume a diet high in beta-carotene (Vitamin A) because research has shown a link to increased lung cancer incidence.

Alternative and Complementary Therapies

There are a great many claims about particular vitamin and or antioxidants having beneficial health effects. Proper nutrition with an adequate diet is the best way to obtain vitamins, but a supplement may be required when intake is inadequate. It is important to check with a dietitian or doctor before taking nutritional supplements or alternative therapies because they may interfere with cancer medications or treatments.

Resources

Books

Quillin, Patrick, and Noreen Quillin. Beating Cancer With Nutrition—Revised. Sun Lakes, AZ: Bookworld Services, 2001.

Periodicals

"Calcium and Vitamin D Collaborate to Reduce Cancer Risk." Health & Medicine Week January 5, 2004: 190.

Sadovsky, Richard. "Can Vitamins Prevent Cancer and Heart Disease?" American Family Physician February 1, 2004: 631.

Singletary, Keith. "Diet, Natural Products and Cancer Chemoprevention." Journal of Nutrition 130 (2000): 465–6.

Willett, Walter C. "Diet and Cancer." The Oncologist 5, no. 5 (2000): 393–404.

Organizations

The National Cancer Institute (NCI). Public Inquiries Office: Building 31, Room 10A31, 31 Center Dr., MSC 2580, Betheseda, MD 20892-2580 (301) 435-3848, (800) 4-CANCER. , , .

National Center for Complementary and Alternative Medicine (NCCAM). 31 Center Dr., Room #5B-58, Bethesda, MD 20892-2182. (800) NIH-NCAM, Fax (301) 495-4957. .

Background

Vitamins are organic compounds that are necessary in small amounts in animal and human diets to sustain life and health. The absence of certain vitamins can cause disease, poor growth, and a variety of syndromes. Thirteen vitamins have been identified as necessary for human health, and there are several more vitamin-like substances that may also contribute to good nutrition. Originally, it was thought that vitamins were particular chemical compounds called amines, but now it is known that the vitamins are unrelated chemically. Their actions are different, and though exhaustively studied, not everything is understood about how they work and what they do. The vitamins are named by letters—vitamin A, vitamin C, D, E, K, and the group of B vitamins. The eight B vitamins were originally thought to be one vitamin, and as more was learned about them, they were given numeral subscripts: vitamin B,, B₂, etc. The B vitamins are now commonly called more aptly by chemically descriptive names: B, is thiamine, B₂ is riboflavin, B₆ and B₁₂ retain their numeral names, and the other B vitamins are niacin, pantothenic acid, biotin, and folic acid. The vitamins are found in plant and animal food sources. They have also been chemically synthesized and so can be ingested in their pure form as nutritional supplements. It is not known precisely how much of each vitamin each person needs, but there are recommended daily allowances for 10 vitamins.

Some researchers have made extravagant claims about the benefits of large doses of specific vitamins as either preventatives or cures for diseases from acne to cancer. As new discoveries are made and old claims are either debunked or reinforced often, it is safest to say that more is understood about the consequences of lack of vitamins than what particular vitamins may do. For example, deficiency of vitamin A leads to break-down of the photosensitive cells in the retina of the eye, causing night blindness. Absence of vitamin C in the diet leads to scurvy, a disease formerly the bane of sailors. Absence of vitamin D may lead to rickets, a bone disease.

History

Many researchers were responsible for piecing together the existence of vitamins as necessary components of the human and animal diets. One of the first people to study nutrition from a chemical standpoint was English physician William Prout. In 1827, he defined the three essentials of the human diet as the oily, the saccharin, and the albuminous, which in modern-day terms are fats and oils, carbohydrates, and proteins. In 1906, an English biochemist, Frederick Hopkins, discovered that mice fed on a pure diet of the three essentials could not survive unless they were given supplementary small amounts of milk and vegetables. A Polish scientist, Casimir Funk, coined the term vitamines in 1912 to describe the chemicals he believed were found in the supplementary food that helped the mice survive. Funk first believed that the vitamines were chemically related amines, thus vita (life) plus amines. As other vitamins were isolated that were not amines, the spelling of the word changed. Other researchers working on diseases such as scurvy and beriberi, which are caused by vitamin deficiency, contributed to the isolation of the different vitamins. Still, little was generally understood about vitamins at the beginning of the twentieth century. For instance, though the use of lime juice to prevent scurvy in sailors dates back to at least 1795, the physician who accompanied Scott's voyage to the South Pole in 1910 believed scurvy was caused by bacteria, and inadequate nutritional measures were taken to prevent the disease among the explorers. Between 1925 and 1955, the known vitamins were all isolated and synthesized. Research continues today on the function of the various vitamins.

Raw Materials

Vitamins can be derived from plant or animal products, or produced synthetically in a laboratory. Vitamin A, for example, can be derived from fish liver oil, and vitamin C from citrus fruits or rose hips. Most commercial vitamins are made from synthetic vitamins, which are cheaper and easier to produce than natural derivatives. So vitamin A may be synthesized from acetone, and vitamin C from keto acid. There is no chemical difference between the purified vitamins derived from plant or animal sources and those produced synthetically. Different laboratories may use different techniques to produce synthetic vitamins, as many can be derived from various chemical reactions.

Vitamin tablets or capsules usually contain additives that aid in the manufacturing process or in how the vitamin pill is accepted by the body. Microcrystalline cellulose, lactose, calcium, or malto-dextrin are added to many vitamins as a filler, to give the vitamin the proper bulk. Magnesium stearate or stearic acid is usually added to vitamin tablets as a lubricant, and silicon dioxide as a flow agent. These additives help the vitamin powder run smoothly through the tablet-making or encapsulating machine. Modified cellulose gum or starch is often added to vitamins as a disintegration agent. That is, it helps the vitamin compound break up once it is ingested. Vitamin tablets are also usually coated, to give the tablets a particular color or flavor, or to determine how the tablet is absorbed (in the stomach versus in the intestine, slowly versus all at once, etc.). Many coatings are made from a cellulose base. An additional coating of carnauba wax is often put on as well, to give the tablet a polished appearance.

Herbs of various kinds may be added to vitamin compounds, as well as minerals such as calcium, iron, and zinc. Typically, specialized laboratories produce purified vitamins and minerals. A distributor buys these from the laboratories and sells them to manufacturers, who put them together in different compounds such as multivitamin tablets or B-complex capsules.

The Manufacturing
Process

Preliminary check

• A vitamin manufacturer purchases raw vitamins and other ingredients from distributors. Raw vitamins from a reputable distributor arrive with a Certificate of Analysis, stating what the vitamins are and how potent they are. In many cases, the manufacturer will nevertheless test the raw materials or send samples to an independent laboratory for analysis. If herbs are to be an ingredient in the vitamin capsule, these must be tested for identity and potency, and for possible bacterial contamination as well.

Preblending

• Often, the raw vitamins arrive at the manufacturer in a fine powder, and they need no preliminary processing. However, if the ingredients are not finely granulated, they will be run through a mill and ground. Some vitamins may be preblended with a filler ingredient such as microcrystalline cellulose or malto-dextrin, because this produces a more even granule which aids further processing steps. Laboratory technicians may run test batches when working with new ingredients and determine if preblending is necessary.

Wet granulation

• For vitamin tablets, particle size is extremely important in determining how well the formula will run through the tabletting machine. In some cases, the raw vitamins arrive from the distributor milled to the appropriate size for tabletting. In other cases, a wet granulation step is necessary. In wet granulation, the fine vitamin powder is mixed with a variety of cellulose particles, then wetted. The mixture is then dried in a dryer. After drying, the formula may be in chunks as large as a dime. These chunks are sized by being run through a mill. The mill forces the chunks through a small hole of the desired diameter of the granule. These granules can then be weighed and mixed.

Weighing and mixing

• When all the vitamin ingredients are ready, a worker takes them to the weigh station and weighs them out on a scale. The required weights for each ingredient in the batch are listed on a formula batch record. After weighing, the worker dumps all the ingredients into a mixer. The volume of a typical mixer may be from 15-30 cu ft (0.42-0.84 cu m), though in a large manufacturing facility, it may be many times that large. The ingredients spend from 15 to 30 minutes in the mixer. At this point, samples are taken from different sides of the mixer and checked in the laboratory. The lab technicians verify that all the ingredients are distributed in the same proportion throughout the mix. If the manufacturer is making a large batch, workers may check the first three or four lots in the mixer, and then only re-check periodically. After mixing is complete, workers take the vitamin formula to either an encapsulating or a tablet-making machine.

Encapsulating machine

• If the lot in the mixer has been approved, workers tote the mixture to the encapsulating machine and dump it in a hopper. At the beginning of a batch, workers will test-run the encapsulating machine and check that the capsules are the proper and consistent weight. Workers also check the capsules visually to see if they seem to be splitting or dimpling. If the test batches run correctly, workers run the entire batch. The vitamin mixture flows through one hopper, and another hopper holds whole gelatin capsules. The capsules are broken into halves by the machine. The bottom half of the capsule falls through a funnel into a rotating dosing dish. Then the machine measures a precise amount of the powdered vitamin mixture into each open capsule half. Tamping pins push the powder down. Then the top halves of the capsules are pushed down onto the filled bottoms.

Polishing and inspection

• The filled vitamin capsules are next run through a polishing machine. The vitamins are circulated on a belt through a series of soft brushes. Any excess dust or vitamin powder is removed from the exterior of the capsules by the brushes. The polished capsules are then poured onto an inspection table. The inspection table has a belt of rotating rods. The vitamins fall in the grooves between the rods, and the vitamins rotate as the rods turn. Thus, all sides of the vitamin are visible for the inspector to see. The inspector removes any capsules that are too long, split, dimpled, or otherwise imperfect. The vitamins that pass inspection are then taken over to the packaging area.

Tableting

• Vitamin tablets are made in a tableting machine. After the vitamin blend has been mixed in the mixer, workers dump it into a hopper above the machine. The vitamin powder then flows through the hopper to a filling station beneath, and flows from there to a rotating table. The rotating table may be 2-4 ft (0.6-1.2m) in diameter, or even bigger, and is fitted with holes on its outside edge that hold dies in the shape of the desired tablet (oval, round, animal, etc.). The dies are interchangeable, so the same table can produce whatever shape the manufacturer wishes, as long as the proper dies are installed. The vitamin powder flows from the filling station to fill the die. When the table rotates, the filled die moves into a punch press. When the upper and lower halves of the punch meet, 4-10 tons (3.6-9 metric tons) of pressure is exerted on the vitamin powder. The pressure compresses the vitamin powder into a compact tablet. The punch releases, and the lower punch lifts to eject the tablet. Some tableting machines may have two punches, one on each side, so two tablets are made simultaneously. The speed of the rotation of the table determines how many tablets are made per minute. The tablets eject onto a vibrating belt which vibrates any loose dust off the tablets. The tablets then are moved to the coating area.

Coating

• 8 Vitamin tablets are usually coated for a variety of reasons. The coating may make the tablet easier to swallow. It may mask an unpleasant taste, and it may give the tablet a pleasant color. A manufacturer may coat in two different colors tablets that are the same size and shape, for identification. Tablets may also be given an enteric coating—a pH sensitive chemical coating that resists gastric acid. Tablets with an enteric coating will not break open in the stomach, but move to the intestine before dissolving. Other coatings determine the timing of the tablet's dissolution, so the vitamins can be absorbed slowly, or all at once, depending on what is appropriate to that tablet.

  Once the tablets are taken from the tableting area, they are placed in the coating pan. The coating pan is a large rotating pan surrounded by one to six spray guns operated by pumps. As the tablets revolve in the pan, the pumps spray coating over them. Many tablets also receive a second coating of carnauba wax. After air drying, the tablets are ready for packaging. The packaging step is the same for tablets as for capsules.

Packaging

• Packaging the vitamins takes several steps, and different machines carry out these steps. So in the packaging area, the vitamins pass through a row of machines. Once the vitamins are dumped in the hopper of the first machine, no human touches them. The worker sets the machine to count out the required number of capsules or tablets per bottle, and the rest is done automatically. The capsules or tablets fall into a bottle, and the bottle is passed to the next machine to be sealed, capped, labelled, and shrink-wrapped. The finished bottles are then set in boxes and are ready for distribution.

Quality Control

Checks for quality are taken at many stages of vitamin manufacturing. All the ingredients of vitamin tablets or capsules are checked for identity and potency before they are used. Often this is tested both by the raw vitamin distributor and by the manufacturer. The mixed vitamin powder is checked before it is tableted or encapsulated, and the finished product is also thoroughly inspected. Federal regulations govern what substances can be used in vitamins and what claims manufacturers can make for their products. Vitamin ingredients must be proven safe before they can be made available to consumers.

The Future

Vitamin research is a volatile field, with new studies constantly suggesting new roles for vitamins in health and prevention of disease. Certain vitamins or vitamin-like substances go through fads of consumer popularity as some of this research surfaces. Nevertheless, the manufacturing process remains the same for new substances. The future of vitamins will likely change most conceptually, in how much we understand about how vitamins work.

Where to Learn More

Books

Bender, David A. Nutritional Biochemistry of the Vitamins. Cambridge University Press, 1992.

Hendler, Sheldon Saul. The Doctor's Vitamin and Mineral Encyclopedia. Simon and Schuster, 1991.

Lieberman, Shari and Nancy Bruning. The Real Vitamin & Mineral Book. Avery Publishing Group, 1990.

[Article by: Angela Woodward]

An organic compound required in very small amounts for the normal functioning of the body and obtained mainly from foods. Vitamins are present in food in minute quantities compared to the other utilizable components of the diet, namely, proteins, fats, carbohydrates, and minerals.

Synthetic and natural vitamins usually have the same biological value. Different vitamins, which are often not related to each other chemically or functionally, are conventionally divided into a fat-soluble group (vitamins A, D, E, and K) and a water-soluble group [vitamin C (ascorbic acid) and the various B vitamins: thiamine, vitamin B, riboflavin, vitamin B₂, vitamin B₆, niacin, folic acid, vitamin B₁₂, biotin, and pantothenic acid]. The vitamins, particularly the water-soluble ones, occur almost universally throughout the animal and plant kingdoms individual articles on each vitamin.

The B vitamins function as coenzymes that catalyze many of the anabolic and catabolic reactions of living organisms necessary for the production of energy; the synthesis of tissue components, hormones, and chemical regulators; and the detoxification and degradation of waste products and toxins. On the other hand, vitamin C and the fat-soluble vitamins do not function as coenzymes. Vitamins C and E and β-carotene (a precursor of vitamin A) act as antioxidants, helping to prevent tissue injury from free-radical reactions. In addition, vitamin C functions as a cofactor in hydroxylation reactions. Vitamin D has hormonelike activity in calcium metabolism; vitamin A plays a critical role in night vision, growth, and maintaining normal differentiation of epithelial tissue; and vitamin K has a unique posttranscriptional role in the formation of active blood-clotting factors. See also Antioxidant; Carotenoid; Coenzyme; Nutrition.

Thirteen organic substances are essential to human life in very small amounts. Eleven of these must be supplied in the diet (vitamins A, B₁, B₂, B₆, B₁₂, C, E, K, folate, biotin, and pantothenate); two (niacin and vitamin D) can be made in the body if there is sufficient of the amino acid tryptophan, and exposure to sunlight respectively.

The word may be pronounced either ‘vaitamin’ or ‘vitamin’.

The vitamins

One of a group of potent, non-protein, organic compounds required in small amounts for the maintenance of normal health and metabolic integrity. Deficiency leads to specific clinical signs that respond only to restoration of the vitamin. They are essential in the diet because they cannot be made in the body (with the exception of vitamin D and niacin). So far, 13 compounds have been classed as true vitamins. Several other substances, such as laetrile and pangamic acid, have been described as vitamins but these compounds do not meet the strict definition of a vitamin. Although vitamins form a diverse and chemically unrelated group, they are classified as fat-soluble vitamins or water-soluble vitamins.

FAT-SOLUBLE VITAMINS
• vitamin A (retinol; carotene is an important precursor of vitamin A)
• vitamin D (ergocalciferol and cholecalciferol)
• vitamin E (tocopherol)
• vitamin K (phylloquinone from plants; menaquinone from gut bacteria)

WATER-SOLUBLE VITAMINS
• vitamin B₁ (thiamin)
• vitamin B₂ (riboflavin)
• vitamin B₆ (pyridoxine)
• vitamin B₁₂ (cobalamin)
• niacin (nicotinic acid and nicotinamide)
• pantothenic acid
• biotin
• folic acid
• vitamin C (ascorbic acid)

Each vitamin has a specific function; one vitamin cannot substitute for another. Lack of any one vitamin in the diet leads to ill health and eventually a deficiency disease. In addition, many body functions require the interaction of several vitamins, and the lack of one may undermine the function of others.

The relationship between vitamin requirements and exercise is complex, and the subject of much debate. There is some dispute about whether active people require more of every type of vitamin. However, it is generally agreed that requirements of the B-complex vitamins, which play many diverse roles in energy metabolism, are directly related to calorie expenditures of up to 5000 Calories per day. On this basis, some coaches believe that very active people may need at least twice the recommended daily amounts of these vitamins. Many sports nutritionists maintain that this increased demand for vitamins can be satisfied by eating a well-balanced diet. They argue that, as energy expenditure increases, food intake and therefore vitamin intake will also increase. On the other hand, some coaches advocate the use of vitamin supplements, arguing that increased dietary intake alone cannot guarantee a sufficient vitamin intake. See also vitamin supplementation.

One of a number of unrelated organic substances that occur in small amounts in food and are required for normal metabolic activity. The vitamins may be water soluble or fat soluble.

Definition

Vitamins are organic components in food that are needed in very small amounts for growth and for maintaining good health. The vitamins include vitamins D, E, A, and K (fat-soluble vitamins), and folate (folic acid), vitamin B₁₂, biotin, vitamin B₆, niacin, thiamin, riboflavin, pantothenic acid, and vitamin C (ascorbic acid) (water-soluble vitamins). Vitamins are required in the diet in only tiny amounts, in contrast to the energy components of the diet. The energy components of the diet are sugars, starches, fats, and oils, and these occur in relatively large amounts in the diet.

Most of the vitamins are closely associated with a corresponding vitamin deficiency disease. Vitamin D deficiency causes rickets, a disease of the bones. Vitamin E deficiency occurs only very rarely and causes nerve damage. Vitamin A deficiency, common throughout the poorer parts of the world, causes night blindness. Severe vitamin A deficiency can result in xerophthalmia, a disease that, if left untreated, results in total blindness. Vitamin K deficiency results in spontaneous bleeding. Mild or moderate folate deficiency, common throughout the world, can result from the failure to eat green, leafy vegetables or fruits and fruit juices. Folate deficiency causes megaloblastic anemia, which is characterized by the presence of large abnormal cells called megaloblasts in the circulating blood. The symptoms of megaloblastic anemia are tiredness and weakness. Vitamin B₁₂ deficiency occurs with the failure to consume meat, milk, or other dairy products. Vitamin B₁₂ deficiency causes megaloblastic anemia and, if severe enough, can result in irreversible nerve damage. Niacin deficiency results in pellagra, which involves skin rashes and scabs, diarrhea, and mental depression. Thiamin deficiency results in beriberi, a disease resulting in atrophy, weakness of the legs, nerve damage, and heart failure. Vitamin C deficiency results in scurvy, a disease that involves bleeding. Diseases associated with deficiencies in vitamin B₆, riboflavin, or pantothenic acid have not been found in the humans, though persons who have been starving or consuming poor diets for several months, might be expected to be deficient in most of the nutrients, including vitamin B₆, riboflavin, and pantothenic acid. Rarely, deficiency in B₆ results in neurologic problems. Issues of toxicity are connected to the over consumptions of vitamins, particularly E, K, and B. Also, lack of regulation in the vitamin industry means consumers ought only to buy well-known brands.

Some of the vitamins serve only one function in the body, while other vitamins serve a variety of unrelated functions. Hence, some vitamin deficiencies tend to result in one type of defect, while other deficiencies result in a variety of problems.

Description

Vitamin treatment is usually done in three ways: by replacing a poor diet with one that supplies the recommended dietary allowance, by consuming oral supplements, or by injections. Injections are useful for persons with diseases that prevent absorption of fat-soluble vitamins. Oral vitamin supplements are especially useful for persons who otherwise cannot or will not consume food that is a good vitamin source, such as meat, milk, or other dairy products. For example, a vegetarian who will not consume meat may be encouraged to consume oral supplements of vitamin B₁₂.

Treatment of genetic diseases which impair the absorption or utilization of specific vitamins may require megadoses of the vitamin throughout one's lifetime. Megadose means a level of about 10 to 1,000 times greater than the RDA. Pernicious anemia, homocystinuria, and biotinidase deficiency are three examples of genetic diseases which are treated with megadoses of vitamins.

General Use

People are treated with vitamins for three reasons. The primary reason is to relieve a vitamin deficiency, when one has been detected. Chemical tests suitable for the detection of all vitamin deficiencies are available. The diagnosis of vitamin deficiency is often aided by visual tests, such as the examination of blood cells with a microscope, the x-ray examination of bones, or a visual examination of the eyes or skin.

A second reason for vitamin treatment is to prevent the development of an expected deficiency. Here, vitamins are administered even with no test for possible deficiency. One example is vitamin K treatment of newborn infants to prevent bleeding. Food supplementation is another form of vitamin treatment. The vitamin D added to foods serves the purpose of preventing the deficiency from occurring in persons who may not be exposed much to sunlight and who fail to consume foods that are fortified with vitamin D, such as milk. Niacin supplementation prevents pellagra, a disease that occurs in people who rely heavily on corn as the main source of food and who do not eat much meat or milk. In general, the American food supply is fortified with niacin.

A third reason for vitamin treatment is to reduce the risk for diseases that may occur even when vitamin deficiency cannot be detected by chemical tests. One example is folate deficiency. The risk for cardiovascular disease can be slightly reduced for a large fraction of the population by folic acid supplements. And the risk for certain birth defects can be sharply reduced in certain women by folic acid supplements.

Vitamin treatment is important during specific diseases in which the body's normal processing of a vitamin is impaired. In these cases, high doses of the needed vitamin can force the body to process or use it in the normal manner. One example is pernicious anemia, a disease that tends to occur in middle age or old age and impairs the absorption of vitamin B₁₂. Surveys have revealed that about 0.1 percent of the general population, and 2–3 percent of the elderly, may have the disease. If left untreated, pernicious anemia leads to nervous system damage. The disease can easily be treated with large oral daily doses of vitamin B₁₂ (hydroxocobalamin) or with monthly injections of the vitamin.

Vitamin supplements are widely available as over-the-counter products. But whether they work to prevent or curtail certain illnesses, particularly in people with a balanced diet, is in the early 2000s a matter of debate and ongoing research. For example, vitamin C is not proven to prevent the common cold. Yet millions of Americans take it for that reason. Consumers should ask a physician or pharmacist for more information on the appropriate use of multivitamin supplements.

The diagnosis of a vitamin deficiency usually involves a blood test. An overnight fast is usually recommended as preparation prior to withdrawal of the blood test so that vitamin-fortified foods do not affect the test results.

The response to vitamin treatment can be monitored by chemical tests, by an examination of red blood cells or white blood cells, or by physiological tests, depending on the exact vitamin deficiency.

Precautions

Vitamin A and vitamin D can be toxic in high doses. Side effects range from dizziness to kidney failure. Consumers should ask a physician or pharmacist about the correct use of a multivitamin supplement that contains these vitamins.

Side Effects

Few side effects are associated with vitamin treatment if vitamins are taken within the prescribed dosages. Excessive intake of some B vitamins may impart a greenish color to urine. Any possible risks depend on the vitamin and the reason why it was prescribed. Consumers should ask a physician or pharmacist about how and when to take vitamin supplements, particularly those that have not been prescribed by a physician.

Parental Concerns

The dosage of vitamin supplements should not exceed the recommended daily allowance without a recommendation by a physician. Recommended dosages vary with age, so parents should be should to give vitamins to children that are specially formulated for children. Vitamin bottles will list recommended doses for different age groups. Infants and toddlers may also benefit from vitamin supplements if they do not eat a variety of foods. Liquid vitamin supplements are available commercially for these young children.

Resources

Books

Heird, William C. "Vitamin Deficiencies and Excesses." In Nelson Textbook of Pediatrics, 17th ed. Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2003, pp. 177–90.

Litwack, Gerald. Vitamins and Hormones. St. Louis, MO: Elsevier, 2004.

Mason, Joel B. "Consequences of Altered Micronutrient Status." In Cecil Textbook of Medicine, 22nd ed. Edited by Lee Goldman et al. Philadelphia: Saunders, 2003, pp. 1326–35.

Navarra, Tova. Encyclopedia of Vitamins, Minerals, and Supplements. New York: Facts on File, 2004.

Russell, Robert M. "Vitamin and Trace Mineral Deficiency and Excess." In Harrison's Principles of Internal Medicine, 15th ed. Edited by Eugene Braunwald et al. New York: McGraw-Hill, 2001, pp. 461–9.

Periodicals

Bryan, J., et al. "Nutrients for cognitive development in school-aged children." Nutrition Reviews 62, no. 8 (2004): 295–306.

Fennell, D. "Determinants of supplement usage." Preventive Medicine 39, no. 5 (2004): 932–9.

Krapels, I. P., et al. "Maternal nutritional status and the risk for orofacial cleft offspring in humans." Journal of Nutrition 134, no. 11 (2004): 3106–13.

Mossad, S. B. "Current and future therapeutic approaches to the common cold." Expert Review of Anti-Infective Therapy 1, no. 4 (2004): 619–26.

Organizations

American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 66211–2672. Web site: www.aafp.org/.

American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007–1098. Web site: www.aap.org/default.htm.

American Association of Naturopathic Physicians. 8201 Greensboro Drive, Suite 300, McLean, VA 22102. Web site: .

American College of Obstetricians and Gynecologists. 409 12th St., SW, PO Box 96920, Washington, DC 20090–6920. Web site: www.acog.org/.

Web Sites

"Dietary Reference Intakes Tables: Vitamins Table." Institute of Medicine of the National Academies. Available online at www.iom.edu/file.asp?id=7296 (accessed January 9, 2005).

"Vitamins." Harvard School of Public Health. Available online at www.hsph.harvard.edu/nutritionsource/vitamins.html (accessed January 9, 2005).

"Vitamins." National Library of Medicine. Available online at www.nlm.nih.gov/medlineplus/ency/article/002399.htm (accessed January 9, 2005).

"Vitamins and Minerals." Food and Nutrition Information Center. Available online at www.nal.usda.gov/fnic/etext/000068.html (accessed January 9, 2005).

"Vitamins and Minerals." West Virginia Dietetic Association. Available online at www.wvda.org/nutrient/ (accessed January 9, 2005).

[Article by: L. Fleming Fallon, Jr., MD, DrPH]

For more information on vitamin, visit Britannica.com.

A member of a group of potent non-protein organic compounds required in minute amounts for good health and growth. Vitamins (except vitamin D) cannot be synthesized by the body and are therefore essential constituents of the diet. They are classified as fat-soluble vitamins (e.g. vitamins A, D, E, and K) or water soluble vitamins (e.g. vitamins B and C). Many vitamins seem to act as coenzymes or are involved in the production of coenzymes. Each vitamin has a specific function; one vitamin cannot substitute for another. Many metabolic reactions require several vitamins and lack of one may hinder the activity of others. There is much disagreement about the effects of exercise on vitamin requirements. Many coaches believe that the added stress experienced by elite athletes makes greater demands on their vitamin requirements, and that they suffer a greater risk of vitamin deficiency than sedentary people. Currently there is much research being undertaken to establish the precise vitamin needs of athletes.

Overview

The word "vitamin" came from the term vita mines (vital amines), which was introduced by Casimir Funk, who, in 1912, isolated a growth factor from rice polishings that contained an amine (a compound incorporating a nitrogen atom with two hydrogen atoms) and could cure the disease beriberi. Several other growth factors were identified early in the twentieth century as well, and these substances were also called vitamins even though they did not contain an amine. Vitamins are classified into two major groups: fat-soluble and water-soluble. (See the Appendix for a complete chart of vitamins.)

Fat-Soluble Vitamins

Vitamin A. In the early 1900s, Sir Frederick Hopkins demonstrated that animals would not grow if lard was provided as a sole dietary lipid. When a small quantity of milk containing fat was added to the diet, the animals thrived. The fat-soluble factor was isolated and designated as vitamin A, later called retinol or retinal; these and similar compounds are referred to as retinoids. Carotenoids, which are essentially two retinoids joined tail to tail, are inactive forms of vitamin A and are called provitamin A. They are converted to vitamin A in the intestine and liver. Vitamin A and carotenoids are absorbed in the chylomicron (a lipoprotein particle that transports lipids from the intestine) fraction and stored in the liver. Some foods such as milk are fortified with vitamin A. Rich sources of carotenoids include carrots, leafy green vegetables, and pink grapefruit.

Vitamin A is, chemically, a subgroup of retinoids, which are defined as a class of compounds that consist of a six-membered ring and a side chain with four conjugated double bonds (four isoprenoid units). The term vitamin A is used to describe retinoids exhibiting qualitatively the biologic activity of the retinoid, retinol.

Vitamin A binds to a retinol-binding protein that transports the light-sensitive vitamin to various target tissues, including the eyes, skin, and gastrointestinal track. The major functions of vitamin A include vision and regulation of cellular proliferation and differentiation. Vitamin A functions on vision by interacting with the rod and cone cells in the retina. It is responsible for absorbing light. The 11-cis form of vitamin A (retinal) combines with the protein opsin to form rhodopsin in the rod cells and iodopsins in the cone cells. The rhodopsin and iodopsins absorb light at various wavelengths and trigger a nerve impulse to the visual cortex in the brain that is ultimately perceived as black-and-white and color vision, respectively.

Vitamin A's other major physiologic function is to maintain the health of skin and mucous-secreting cells by regulating their cellular activity and maturation. The dietary requirements depend on age.

The major consequence of vitamin A deficiency, which continues to be a serious nutritional problem among millions of schoolchildren in southern and southeastern Asia and parts of Africa and South America, is night blindness. Vitamin A deficiency can lead to complete blindness and severe damage to the outer covering of the eye (the cornea), often causing it to perforate, with loss of the fluid from inside the eye (keratomalacia). Vitamin A deficiency also produces changes in the skin that are related to the inability of the skin cells to mature and produce keratin properly. This leads to follicular hyperkeratosis and phrynoderma (a condition characterized by rough, dry skin). Vitamin A deficiency has also been linked to increased mortality in early childhood.

Acute and chronic ingestion of excessive amounts of vitamin A can cause a multitude of symptoms and consequences. The most serious is that it can cause severe birth defects, spontaneous abortions and learning defects, and skin and epithelial-cell exfoliation. Inexperienced white explorers of the Arctic who ate polar-bear liver in excess developed severe vitamin A intoxication that caused a total sloughing of their skin and mucoussecreting cells in the upper airway and esophagus, bringing on painful death. (This is in contrast to the indigenous Inuit, who specifically avoid eating polar-bear liver.)

Vitamin D. One of the consequences of the industrial revolution was the high incidence of the bone-deforming disease rickets. It was estimated, at the turn of the twentieth century, that more than ninety percent of children living in the industrialized cities of northern Europe and the northeastern United States had rickets. It had been known that cod-liver oil possessed a factor that had antirachitic activity. Originally, it was thought that the antirachitic factor was vitamin A. However, Hopkins heated cod-liver oil to destroy the vitamin A activity and demonstrated that it still possessed antirachitic activity. This new fat-soluble vitamin was labeled vitamin D. It was also recognized that exposure of food, animals, and humans to ultraviolet radiation also prevented and cured rickets.

There are two principal forms of vitamin D: Vitamin D ₂ comes from the precursor ergosterol found in yeast and plants, and vitamin D ₃ comes from the cholesterol precursor 7-dehydrocholesterol that is found in the skin of reptiles, birds, mammals, and humans. Vitamin D ₂ and vitamin D ₃ are essentially equally active in most birds and in most mammals, including humans. Chickens and New World monkeys, however, cannot utilize vitamin D ₂. There are very few foods that naturally contain vitamin D. Fatty fish, such as salmon and mackerel, and fish-liver oils, such as cod-liver oil are good sources of vitamin D. Cow's milk and human milk have very little vitamin D. However, in the United States and Canada, milk and some breads and cereals are fortified with vitamin D. In Europe, fortification of foods with vitamin D was outlawed when sporadic cases of vitamin D intoxication were observed in children in the 1950s. Today some margarine and cereals are fortified with vitamin D in Europe, but milk is not.

Vitamin D ₃ is made by the action of sunlight on the skin. Provitamin D ₃ (7-Dehydrocholesterol) absorbs solar ultraviolet B radiation (wavelengths 290–315 nm) and is transformed into previtamin D ₃. Previtamin D ₃ is unstable at body temperature and isomerizes (rotates its double bonds) to vitamin D ₃. Once formed, vitamin D ₃ leaves the skin and enters the circulation, bound to the vitamin D binding protein. It travels to the liver where it is activated to 25-hydroxyvitamin D [25(OH)D]. This form, however, is biologically inert at physiologic concentrations and is the major circulating form of vitamin D. It is, nevertheless, the form that is measured to determine the vitamin D status of an individual, because it represents a summation of dietary and skin sources of vitamin D. 25(OH)D is transported on the vitamin D binding protein to the kidney, where it undergoes its final activation on carbon 1 to form 1,25-dihydroxyvitamin D [1,25(OH) ₂D], the biologically active form of vitamin D.

The principal function of vitamin D is to maintain blood calcium and phosphorus in the normal range in order to promote neuromuscular function and to maintain metabolic activities. It accomplishes this by enhancing the efficiency of intestinal calcium transport in the small intestine and by stimulating precursor cells of osteoclasts to become mature osteoclasts. Among the functions of osteoclasts is to remove calcium from bone. Serum calcium and phosphorus are in the form of Ca _x(PO ₄). When these compounds are in the normal range, they are in a supersaturated state that can thus be deposited in the skeletal matrix as calcium hydroxyapatite.

1,25(OH) ₂D interacts with a receptor in the nucleus of cells, known as the VDR (vitamin D receptor). It also complexes with the "retinoic acid x" receptor in that cellular structure. These receptor-activated vitamin D complexes find their way to genes that have responsive elements known as the vitamin D-responsive element. These elements in turn unlock genetic information that is responsible for various biologic functions in intestine and bone. It is recognized that a wide variety of tissues including the brain, parathyroid glands, breast, pro state, stomach, and skin also have VDR. Although the exact physiologic function of 1,25(OH) ₂D in these non-calcium-regulating tissues is not well understood, 1,25(OH) ₂D inhibits cellular proliferation and induces terminal differentiation of a wide variety of cells, including bone, skin, skeletal muscle, breast, and prostate. The dietary requirement depends on age.

Vitamin D deficiency results in a decrease in the efficiency of intestinal calcium absorption that in turn leads to a decrease in unbound or free calcium concentrations in the circulation. This is recognized by the parathyroid gland and results in an increase in the production and secretion of parathyroid hormone (PTH). PTH enhances calcium reabsorption by the kidney and causes increased output of phosphate in the urine. PTH also stimulates the kidney to produce more 1,25(OH) ₂D. The net effect of vitamin D deficiency is a low-normal serum calcium and a low serum phosphorus (due to the PTH-induced phosphate wasting in the kidney). Thus calcium and phosphorus concentrations fall below supersaturating levels, thereby resulting in poorly mineralized bone. In children, this causes rickets and, in adults, osteomalacia. In addition, vitamin D deficiency in adults can precipitate and exacerbate osteoporosis. In winter, little if any vitamin D can be made in the skin of people who live above 40° north or below 40° south of the equator. An increase in the zenith angle of the sun due to latitude, time of day, and season of the year will dramatically reduce the production of vitamin D ₃ in the skin. Moreover, aging and sunscreen use can markedly reduce the production of vitamin D by more than 60 percent and 99 percent, respectively. Rickets due to vitamin D deficiency in children may include bowlegs or knock-knees, widening of the ends of the long bones, growth retardation, and muscle weakness. In adults, in addition to osteomalacia and increased risk of osteoporosis, it causes bone pain, muscle weakness, and fractures.

The safe upper limit for Vitamin D is 2,000 units a day. Although it is difficult to ingest enough to cause vitamin D intoxication, it can occur. Usually, oral ingestion of 10,000 units a day and greater will cause vitamin D intoxication. This intoxication causes an elevation in the blood levels of calcium and phosphorus, which results in the calcification of soft tissues, including the kidney and major blood vessels, and may also cause the formation of kidney stones.

Vitamin E. The discovery of vitamin E (tocopherols—from toc- meaning 'childbirth', phero- meaning 'bringing forth', and -ol representing the alcohol portion of the molecule) was due to the observation that supplementation of the diet with vitamin E prevented fetal death in animals that were fed a diet containing rancid lard. There are eight naturally occurring vitamin E compounds. Four of them are known as tocopherols and four are known as tocotrienols. The most abundant form of vitamin E is alpha-tocopherol. One of the major functions of vitamin E is to act as a biologic antioxidant to protect the sensitive cellular membranes from oxidative destruction. The major sources of vitamin E consumed by Americans are vegetables and seed oils, such as corn oil, soybean oil, and safflower oil. Wheat germ is a rich source of vitamin E. Although butter contains very little vitamin E, American margarine contains a significant amount of this antioxidant vitamin.

Vitamin E, like the other fat-soluble vitamins, is absorbed in the chylomicron fraction into the lymphatic system and is transported into the venous blood. The dietary requirements depend on age.

There have been difficulties in defining a clinical syndrome that correlates with vitamin E deficiency in humans. Vitamin E deficiency is associated with anemia in newborns.

Toxicity from excess vitamin E has been associated with increased bleeding tendency in adults and impaired immune function, decreased levels of vitamin K-dependent clotting factors, and impairment of leukocyte function.

Vitamin K. Vitamin K was discovered by Henrik Dam in Copenhagen in 1929. He observed that chicks fed a fat-free diet developed severe bleeding under the skin and in the muscle and other tissues. He named this new fatsoluble vitamin, vitamin K (for "Koagulation vitamin"). Vitamin K is distributed widely in both animal and vegetable foods as well as in milk. It comes in several forms: vitamin K ₁ comes from plants and is known as phylloquinone, and vitamin K ₂, first isolated from fish meal and in animal foods, comprises a group of compounds known as menaquinones. In addition, bacterial flora in the intestine synthesize menaquinones that are bioavailable.

Vitamin K, like other fat-soluble vitamins, is absorbed in the chylomicron fraction and then appears in the lymph and subsequently in the venous circulation. The major physiologic function of vitamin K is to activate blood-clotting proteins. This is accomplished by the modification of a substance, glutamate, found in several precoagulant factors, including factors II, VII, VIIII, and X, that are produced in the liver. Vitamin K is also re sponsible for the modification of other proteins, including the major noncollagenous protein in bone. The dietary requirements depend on age.

Vitamin K deficiency is rare because of the widespread distribution of the vitamin in plant and animal foods and because microbiotic flora in the normal gut synthesize menaquinones. However, vitamin K deficiency in breast-fed newborns remains a major worldwide cause of infant morbidity and mortality. Infants have very little stored vitamin K at birth, and the gut is nearly sterile during the first few days of life. As a result, infants can develop a severe bleeding condition known as hemorrhagic disease of the newborn if they do not obtain vitamin K during the first few days of life from an exogenous source, particularly since mother's milk contains little vitamin K and few bacteria other than those it picks up from maternal skin as an infant suckles. Adults who have intestinal malabsorption syndrome and who are taking antibiotics can become severely vitamin K-deficient. This can lead to generalized bleeding from all orifices.

There are no reported cases of intoxication due to excessive ingestion of phylloquinone. Ingestion of excessive amounts of menadione, a vitamin K precursor, can cause anemia secondary to the destruction of red blood cells, and an alteration in bilirubin metabolism causing hyperbilirubinemia in infants (kernicterus).

Water-Soluble Vitamins

Thiamine (vitamin B₁). Beriberi is a disease with a constellation of systems affecting the nervous and cardiovascular systems. It was first described by the Chinese in 2697 B.C.E. In 1926, B. C. P. Jansen and W. F. Donath identified a factor from rice-bran extracts that prevented beriberi. The antiberiberi factor was identified chemically and called thiamine (vitamin B₁). Thiamine is found in yeast, lean pork, and legumes. It serves as a receptor for high-energy pyrophosphate. It is this form of the vitamin that provides its chemical function. Pyrophosphate is extremely important for the generation of energy in the cell. However, it cannot enter the cell unless it is attached to thiamine. Thiamine is absorbed by the small intestine and transported to the liver. The major biochemical function of thiamine is to act as a coenzyme (that is, to provide a transfer site) in the alpha-keto acid carboxylation pathway. The dietary requirements depend on age.

Thiamine deficiency causes beriberi. Anorexia, neuritis, gastrointestinal dysfunction, cardiac irregularities, and muscle atrophy are present. There are three types of this disorder: wet, dry, and infantile. Wet beriberi is associated with body fluid retention (edema). Dry beriberi is related to neurologic abnormalities. It is recognized that alcoholics who have poor nutrition and thiamine deficiency, when receiving intravenous fluids, for example in the emergency room of a hospital, can develop severe altered mental states known Wernicke's and Korsakoff's syndromes. Wet beriberi is associated with heart abnormalities; dry beriberi is associated with neurological abnormalities that can cause permanent confusion if not treated in a timely manner.

Excessive ingestion of thiamine is cleared by the kidneys. There is no evidence that ingesting excessive amounts causes toxicity.

Riboflavin. In the 1920s, another water-soluble vitamin was discovered; it exhibited antipellagra activity and was termed vitamin B₂. The substance was found to be yellow in color and was identified as a coenzyme, riboflavin 5'-phosphate (flavin mononucleotide or FMN).

The more abundant form of this vitamin is a complex flavin-adenine dinucleotide (FAD) that also participates as a coenzyme. Usually, the FMN and FAD are associated loosely with proteins and are released in the acidic gastrointestinal juices. The vitamin is absorbed by the proximal small intestine. Sources of riboflavin include eggs, lean meats, milk, broccoli, and enriched breads and cereals.

The physiologic function of riboflavin is to participate in oxidation-reduction reactions in numerous metabolic pathways and in energy production via the respiratory chain in the mitochondria. The dietary requirements depend on age.

Riboflavin is distributed widely in foodstuffs, and therefore deficiency is not common. However, there are reported cases of deficiency that are characterized by sore throat, hyperemia and edema of the pharyngeal and oral mucosal membranes, cheilosis (abnormal scaling and fissuring of the lips), angular stomatitis (surface inflammation of the mouth), glossitis (inflammation of the tongue), seborrheic dermatitis (an inflammation of the skin involving oversecretion by the oil-producing cutaneous glands), and anemia. Severe riboflavin deficiency can affect the conversion of vitamin B₆ to its coenzyme and reduce the conversion of tryptophan, an amino acid found in proteins of animal and plant origin, to niacin (see next section). Deficiency is principally due to abnormal digestion, abnormal absorption, or both. People who are lactose-intolerant—a condition that is most common among blacks and Asians—often limit consumption of milk (as noted above, an excellent source of riboflavin); they may therefore be at increased risk for riboflavin deficiency. Intestinal malabsorption syndromes, including tropical sprue celiac disease, small bowel resection, and gastrointestinal and biliary obstruction can lead to riboflavin deficiency.

There is no evidence that toxicity can occur as a result of excessive ingestion of riboflavin. The most likely reason for this is that riboflavin is cleared rapidly by the kidney and is not stored in the body.

Niacin. In the mid-1700s, a Spanish physician, Gaspar Casal, recognized a disease known as pellagra that caused diarrhea, dementia, and dermatitis in maize-eating (corneating) populations throughout the world. In 1937, Conrad Elvehjem and his colleagues observed that nicotinic acid was an effective treatment for pellagra. Nicotinic acid is synonymous with both niacin and nicotinamide. It is associated with ribose lyphosphate to form nicotinamide adenine dinucleotide (NAD) and NAD phosphate. Most niacin in food is present as a component of NAD or NADP and is relatively stable to cooking and storage. Good sources of niacin include meats (especially liver), fish, legumes such as peanuts, some nuts, and some cereals. Both coffee and tea also contain reasonable amounts of this vitamin. Niacin is unique among the B vitamins because its precursor amino acid, tryptophan, can help meet the daily niacin requirement.

Niacin has a multitude of physiologic functions in a wide variety of metabolic pathways that are related to energy production and biosynthetic processes. At least two hundred enzymes are dependent on NAD and NADP. Both of these substances act as electron acceptors or hydrogen donors. Most NAD-dependent enzymes are involved in catabolic reactions, whereas NADP is used more commonly for reductive biosyntheses of fatty acids and steroids, for example. The dietary requirements depend on age.

Niacin deficiency causes pellagra. This condition is associated with diarrhea, dementia, and dermatitis. It is endemic in India and in parts of China and Africa. The classic appearance of pellagra is a pigmented rash that develops symmetrically in areas of the skin exposed to sunlight. The tongue can become bright red and there is often vomiting and diarrhea. Patients can also exhibit anxiety or sleeplessness, and can become disoriented and delusional.

Nicotinic acid is now used to treat hypercholesterolemia. Side effects of large amounts of nicotinic acid include flushing of the skin, abnormalities in liver function, and hyperglycemia. At extremely high ingestion levels, nicotinamide causes death in rats.

Pyridoxine (vitamin B₆ ). Vitamin B₆ was identified in the 1930s. Like many of the water-soluble B vitamins, vitamin B₆ includes a group of compounds that act as a coenzyme phosphate donor. These include pyridoxal 5>-phosphate (PLP), and pyridoxamine 5>-phosphate (PMP). Plants foods contain predominantly pyridoxine, whereas animal products contain primarily pyridoxal and pyridoxamine. Vitamin B₆ is absorbed mainly by the lower small intestine (jejunum).

Like many of the other coenzyme B vitamins, vitamin B₆ has numerous biologic functions that are related to metabolism. B₆ is critically important for the production of glucose. PLP is also necessary for the conversion of tryptophan to niacin, which is why the two are often associated. The dietary requirements depend on age.

As with many of the other B vitamins, there are a wide variety of clinical symptoms associated with vitamin B₆ deficiency including an abnormal electroencephalogram, convulsions, stomatitis, cheilosis, glossitis, irritability, depression, and confusion.

High doses of pyridoxine have been used to treat premenstrual syndrome and other neurological diseases. Such uses have resulted in neurotoxicity and photosensitivity.

Pantothenic acid. Pantothenic acid was one of the more difficult vitamins to isolate and separate from the other water-soluble B vitamins. Finally in the 1940s, it was synthesized and was found to be associated with coenzyme A (CoA). CoA is an essential cofactor for biologic acetylation reactions and participates in the respiratory tricarboxcylic acid cycle, fatty-acid synthesis and degradation, and a wide variety of other metabolic and regulatory processes. The dietary requirements depend on age.

Pantothenic acid deficiency affects the adrenal gland, nervous system, skin, and hair adversely. Pantothenic acid deficiency in humans is rare, but has been associated with fatigue and depression.

High doses of calcium pantothenate have not been found to be toxic in humans.

Folic acid and cobalamin (vitamin B₁₂ ). In the mid-1800s, several physicians recognized that a severe form of anemia was associated with disorders of the digestive system. In 1934, William Castle and his associates observed that normal human gastric juice contained an intrinsic factor (IF) that combines with an extrinsic factor in animalprotein food, resulting in the absorption of a vitamin that prevents anemia. Vitamin B₁₂ was isolated in 1948 and was shown to be the extrinsic antianemia factor.

Vitamin B₁₂ absorption is unique among the B vitamins, in requiring an IF to help its absorption. Folate, on the other hand, is absorbed directly by the upper (proximal) small intestine.

Whereas vitamin B₁₂ is found only in animal protein, folates are common in nature and present in nearly all natural foods. The dietary requirements depend on age.

Vitamin B₁₂ deficiency can occur either because of inadequate vitamin B₁₂ ingestion or because of the loss or inadequacy of production of intrinsic factor in the stomach. The two most notable clinical signs of vitamin B₁₂ deficiency include megaloblastic anemia and neurological deficits. Vitamin B₁₂ deficiency can cause paresthesia (especially numbness and tingling in the hands and feet); the diminution of vibration and position sense; unsteadiness; poor muscular coordination with ataxia (loss of muscular coordination); moodiness; mental slowness; poor memory; confusion; agitation; depression; and central visual loss. Delusions, overt psychosis, and paranoid ideas may occur in severe deficiency.

Folate deficiency also causes megaloblastic anemia and can cause neurological abnormalities as well, including irritability, forgetfulness, and hostile and paranoid behavior. For adults, ingestion of ten thousand times the minimum requirement for B₁₂ and several hundred times that for folic acid has not been associated with toxicity.

Biotin. Biotin was identified in the 1940s. It, like many of the other B vitamins, acts as a coenzyme. Biotin is plentiful in foods such as liver, egg yolk, soybeans, yeast, cereals, legumes, and nuts. With the exception of cauliflower and mushrooms, vegetables, fruits, and meats, however, are poor sources of biotin. Biotin is also present in human and cow's milk. The major physiologic functions of biotin are related to carbohydrate and lipid metabolism. The dietary requirements depend on age.

Biotin deficiency causes mental-status changes, myalgia (muscle pain), hyperesthesia (abnormal sensitivity to pain, touch, cold, etc.), localized paresthesia, and anorexia with nausea. Dermatitis can also be associated with deficiency. The immune system is impaired in biotin-deficient animals. Neurological disorders including seizures and developmental delays have been reported in children. There have been no reports of intoxication due to excessive biotin ingestion.

Vitamin C. Scurvy is recognized as a deficiency disease that has taken a high toll in human suffering and death. The disease, which is caused by vitamin C deficiency, was recognized in ancient times by the Egyptians, Greeks, and Romans. It was especially prevalent among sea explorers of the sixteenth to eighteenth centuries. Typically, sailors developed bleeding and rotting gums, swollen and inflamed joints, dark blotches on the skin, and muscle weakness that occurred within months when at sea. It was the loss of 1,051 sailors in 1774 that prompted the British Admiralty to seek a cure for this devastating disease. They found that lemon or lime juice could prevent the disease. In the late 1920s, Albert Szent-Györgyi and Glenn King isolated vitamin C and identified it as hexuronic acid. Vitamin C is water-soluble and is absorbed efficiently by the small intestine. Its major physiologic function is to provide reducing activity for a wide variety of metabolic steps. It is important for the modification of lysine and proline—two amino acids that are common components of collagen. These modifications result in the cross-linking of collagen strands providing structural support for this essential component of bone and fibrous tissues. The dietary requirements depend on age.

As noted, vitamin C deficiency causes scurvy, which is associated with a wide variety of abnormalities, including hemorrhages under the skin, black-and-blue marks, hyperkeratosis, joint discomfort, edema, weakness, fatigue, lassitude, depression, and hysteria.

It was suggested by the Nobel Prize Laureate Linus Pauling that extremely high doses of vitamin C could prevent cancer. With the exception of excessive amounts of vitamin C causing bowel impaction via a large number of vitamin C tablets ingested, there are very few serious consequences from an overingestion of vitamin C, though it can increase the risk of kidney stones and other renal diseases.

Other nutrients. Other nutrients that are essential could be considered vitamins. These include choline, carnitine, inositol, and taurine.

Bibliography

Frisell, W. R., ed. Human Biochemistry. New York: Macmillan, 1982.

Holick, Michael F. "Vitamin D: New Horizons for the 21st Century" (McCollum Award Lecture, 1994). The American Journal of Clinical Nutrition 60 (1994): 619–630.

Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, D.C.: National Academy Press, 2001.

Institute of Medicine. "Vitamin D." In Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride, pp. 250–287. Washington, D.C.: National Academy Press, 1997.

Shils, M. E., J. A. Olson, and M. Shike, eds. Modern Nutrition in Health and Diseases. 8th ed. Philadelphia: Lea and Febiger, 1994.

—Michael Holick

Complex organic compounds that are needed in small amounts by the body for normal growth and metabolism. An important part of a balanced diet, vitamins occur naturally in foods and may be added to processed foods to increase their nutritional value. Many vitamins have been identified, and each plays a specific role in the functioning of the body. For example, vitamin C is needed for the proper healing of wounds and broken bones; vitamin A helps the body resist infection. Some vitamins are so important that without them certain diseases or conditions could develop. For example, a deficiency of vitamin D may cause rickets, and a deficiency of vitamin B₁₂ could result in a form of anemia.

An organic substance found in foods and essential in small quantities for growth, health and survival. The body needs vitamins as well as other food constituents such as proteins, fats, carbohydrates, minerals and water. The absence of one or more vitamins from the diet, or poor absorption of vitamins, can cause deficiency diseases such as rickets, enzootic muscular dystrophy and polioencephalomalacia.
Vitamins serve as coenzymes or cofactors in enzymatic reactions. They are required only in trace quantities because they are not consumed in the reactions.

• fat-soluble v. — one soluble in and absorbed from the intestine in fat. Includes vitamins A, D, E and K.
• water-soluble v. — one soluble in water. Includes vitamins B and C.

If we take vitamins on a daily basis, then a dream about vitamins could simply be a reflection of our daily activity. Or, it could represent a concern about health. Vitamins can symbolize that we need to feed our minds with ideas that are "good for us."

This article is about the organic compound. For the nutritional supplement preparation, see multivitamin.

Fruits and vegetables are often a good source of vitamins.

A vitamin is an organic compound required as a nutrient in tiny amounts by an organism.^[1] A compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on the circumstances and the particular organism. For example, ascorbic acid functions as vitamin C for some animals but not others, and vitamins D and K are required in the human diet only in certain circumstances.^[2] The term vitamin does not include other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids, nor does it encompass the large number of other nutrients that promote health but are otherwise required less often.^[3]

Vitamins are classified by their biological and chemical activity, not their structure. Thus, each "vitamin" may refer to several vitamer compounds that all show the biological activity associated with a particular vitamin. Such a set of chemicals are grouped under an alphabetized vitamin "generic descriptor" title, such as "vitamin A," which includes the compounds retinal, retinol, and many carotenoids.^[4] Vitamers are often inter-converted in the body.

Vitamins have diverse biochemical functions, including function as hormones (e.g. vitamin D), antioxidants (e.g. vitamin E), and mediators of cell signaling and regulators of cell and tissue growth and differentiation (e.g. vitamin A).^[5] The largest number of vitamins (e.g. B complex vitamins) function as precursors for enzyme cofactor bio-molecules (coenzymes), that help act as catalysts and substrates in metabolism. When acting as part of a catalyst, vitamins are bound to enzymes and are called prosthetic groups. For example, biotin is part of enzymes involved in making fatty acids. Vitamins also act as coenzymes to carry chemical groups between enzymes. For example, folic acid carries various forms of carbon group – methyl, formyl and methylene - in the cell. Although these roles in assisting enzyme reactions are vitamins' best-known function, the other vitamin functions are equally important.^[6]

Until the 1900s, vitamins were obtained solely through food intake, and changes in diet (which, for example, could occur during a particular growing season) can alter the types and amounts of vitamins ingested. Vitamins have been produced as commodity chemicals and made widely available as inexpensive pills for several decades,^[7] allowing supplementation of the dietary intake.

Retinol (one vitamer of Vitamin A)

Contents 1 History 2 In humans 2.1 Water-soluble 2.2 Fat-soluble 2.3 List of vitamins 3 In nutrition and diseases 3.1 Deficiencies 3.2 Side effects and overdose 4 Supplements 4.1 Governmental regulation of vitamin supplements 5 Names in current and previous nomenclatures 6 See also 7 References 8 External links

History

The Ancient Egyptians knew that feeding a patient liver (back, right) would help cure night blindness.

The value of eating a certain food to maintain health was recognized long before vitamins were identified. The ancient Egyptians knew that feeding liver to a patient would help cure night blindness, an illness now known to be caused by a vitamin A deficiency.^[8] The advancement of ocean voyage during the Renaissance resulted in prolonged periods without access to fresh fruits and vegetables, and made illnesses from vitamin deficiency common among ship's crew.

In 1749, the Scottish surgeon James Lind discovered that citrus foods helped prevent scurvy, a particularly deadly disease in which collagen is not properly formed, causing poor wound healing, bleeding of the gums, severe pain, and death.^[8] In 1753, Lind published his Treatise on the Scurvy, which recommended using lemons and limes to avoid scurvy, which was adopted by the British Royal Navy. This led to the nickname Limey for sailors of that organization. Lind's discovery, however, was not widely accepted by individuals in the Royal Navy's Arctic expeditions in the 19th century, where it was widely believed that scurvy could be prevented by practicing good hygiene, regular exercise, and by maintaining the morale of the crew while on board, rather than by a diet of fresh food.^[8] As a result, Arctic expeditions continued to be plagued by scurvy and other deficiency diseases. In the early 20th century, when Robert Falcon Scott made his two expeditions to the Antarctic, the prevailing medical theory was that scurvy was caused by "tainted" canned food.^[8]

In 1881, Russian surgeon Nikolai Lunin studied the effects of scurvy while at the University of Tartu in present-day Estonia.^[9] He fed mice an artificial mixture of all the separate constituents of milk known at that time, namely the proteins, fats, carbohydrates, and salts. The mice that received only the individual constituents died, while the mice fed by milk itself developed normally. He made a conclusion that "a natural food such as milk must therefore contain, besides these known principal ingredients, small quantities of unknown substances essential to life."^[9] However, his conclusions were rejected by other researchers when they were unable to reproduce his results. One difference was that he had used table sugar (sucrose), while other researchers had used milk sugar (lactose) that still contained small amounts of vitamin B.

The discovery of vitamins and their sources

Year of discovery	Vitamin	Source
1909	Vitamin A (Retinol)	Cod liver oil
1912	Vitamin B1 (Thiamine)	Rice bran
1912	Vitamin C (Ascorbic acid)	Lemons
1918	Vitamin D (Calciferol)	Cod liver oil
1920	Vitamin B2 (Riboflavin)	Eggs
1922	Vitamin E (Tocopherol)	Wheat germ oil, Cosmetic and Liver
1926	Vitamin B12 (Cyanocobalamin)	Liver
1929	Vitamin K (Phylloquinone)	Alfalfa
1931	Vitamin B5 (Pantothenic acid)	Liver
1931	Vitamin B7 (Biotin)	Liver
1934	Vitamin B6 (Pyridoxine)	Rice bran
1936	Vitamin B3 (Niacin)	Liver
1941	Vitamin B9 (Folic acid)	Liver

In east Asia, where polished white rice was the common staple food of the middle class, beriberi resulting from lack of vitamin B1 was endemic. In 1884, Takaki Kanehiro, a British trained medical doctor of the Japanese Navy, observed that beriberi was endemic among low-ranking crew who often ate nothing but rice, but not among crews of Western navies and officers who consumed a Western-style diet. Kanehiro initially believed that lack of protein was the chief cause of beriberi. With the support of the Japanese navy, he experimented using crews of two battleships; one crew was fed only white rice, while the other was fed a diet of meat, fish, barley, rice, and beans. The group that ate only white rice documented 161 crew members with beriberi and 25 deaths, while the latter group had only 14 cases of beriberi and no deaths. This convinced Kanehiro and the Japanese Navy that diet was the cause of beriberi. This was confirmed in 1897, when Christiaan Eijkman discovered that feeding unpolished rice instead of the polished variety to chickens helped to prevent beriberi in the chickens. The following year, Frederick Hopkins postulated that some foods contained "accessory factors"—in addition to proteins, carbohydrates, fats, et cetera—that were necessary for the functions of the human body.^[8] Hopkins was awarded the 1929 Nobel Prize for Physiology or Medicine with Christiaan Eijkman for their discovery of several vitamins.

In 1910, Japanese scientist Umetaro Suzuki succeeded in extracting a water-soluble complex of micronutrients from rice bran and named it aberic acid. He published this discovery in a Japanese scientific journal.^[10]

When the article was translated into German, the translation failed to state that it was a newly discovered nutrient, a claim made in the original Japanese article, and hence his discovery failed to gain publicity. Polish biochemist Kazimierz Funk isolated the same complex of micronutrients and proposed the complex be named "Vitamine" (a portmanteau of "vital amine") in 1912.^[11] The name soon became synonymous with Hopkins' "accessory factors", and by the time it was shown that not all vitamins were amines, the word was already ubiquitous. In 1920, Jack Cecil Drummond proposed that the final "e" be dropped to deemphasize the "amine" reference after the discovery that vitamin C had no amine component.

Throughout the early 1900s, the use of deprivation studies allowed scientists to isolate and identify a number of vitamins. Initially, lipid from fish oil was used to cure rickets in rats, and the fat-soluble nutrient was called "antirachitic A". Thus, the first "vitamin" bioactivity ever isolated, which cured rickets, was initially called "vitamin A", although confusingly the bioactivity of this compound is now called vitamin D.^[12] What we now call "vitamin A" was identified in fish oil as a separate factor that was inactivated by ultraviolet light. In 1931, Albert Szent-Györgyi and a fellow researcher Joseph Svirbely determined that "hexuronic acid" was actually vitamin C and noted its anti-scorbutic activity. In 1937, Szent-Györgyi was awarded the Nobel Prize for his discovery. In 1943 Edward Adelbert Doisy and Henrik Dam were awarded the Nobel Prize for their discovery of vitamin K and its chemical structure.

In humans

Vitamins are classified as either water-soluble or fat soluble. In humans there are 13 vitamins: 4 fat-soluble (A, D, E and K) and 9 water-soluble (8 B vitamins and vitamin C).

Water-soluble

Water-soluble vitamins dissolve easily in water, and in general, are readily excreted from the body, to the degree that urinary output is a strong predictor of vitamin consumption.^[13] Because they are not readily stored, consistent daily intake is important.^[14] Many types of water-soluble vitamins are synthesized by bacteria.^[15]

Fat-soluble

Fat-soluble vitamins are absorbed through the intestinal tract with the help of lipids (fats). Because they are more likely to accumulate in the body, they are more likely to lead to hypervitaminosis than are water-soluble vitamins. Fat-soluble vitamin regulation is of particular significance in cystic fibrosis.^[16]

List of vitamins

Each vitamin is typically used in multiple reactions and, therefore, most have multiple functions.^[17]

Vitamin generic descriptor name	Vitamer chemical name(s) (list not complete)	Solubility	Recommended dietary allowances (male, age 19–70)[18]	Deficiency disease	Upper Intake Level (UL/day)[18]	Overdose disease
Vitamin A	Retinoids (retinol, retinoids and carotenoids)	Fat	900 µg	Night-blindness and Keratomalacia[19]	3,000 µg	Hypervitaminosis A
Vitamin B1	Thiamine	Water	1.2 mg	Beriberi, Wernicke-Korsakoff syndrome	N/D[20]	Rare hypersensitive reactions resembling anaphylactic shock—injection only; Drowsiness
Vitamin B2	Riboflavin	Water	1.3 mg	Ariboflavinosis	N/D	?
Vitamin B3	Niacin, niacinamide	Water	16.0 mg	Pellagra	35.0 mg	Liver damage (doses > 2g/day)[21] and other problems
Vitamin B5	Pantothenic acid	Water	5.0 mg[22]	Paresthesia	N/D	?
Vitamin B6	Pyridoxine, pyridoxamine, pyridoxal	Water	1.3–1.7 mg	Anemia[23] peripheral neuropathy.	100 mg	Impairment of proprioception, nerve damage (doses > 100 mg/day)
Vitamin B7	Biotin	Water	30.0 µg	Dermatitis, enteritis	N/D	?
Vitamin B9	Folic acid, folinic acid	Water	400 µg	Deficiency during pregnancy is associated with birth defects, such as neural tube defects	1,000 µg	Possible decrease in seizure threshold
Vitamin B12	Cyanocobalamin, hydroxycobalamin, methylcobalamin	Water	2.4 µg	Megaloblastic anemia[24]	N/D	No known toxicity[25]
Vitamin C	Ascorbic acid	Water	90.0 mg	Scurvy	2,000 mg	Vitamin C megadosage
Vitamin D	Ergocalciferol, cholecalciferol	Fat	5.0 µg–10 µg[26]	Rickets and Osteomalacia	50 µg	Hypervitaminosis D
Vitamin E	Tocopherols, tocotrienols	Fat	15.0 mg	Deficiency is very rare; mild hemolytic anemia in newborn infants.[27]	1,000 mg	Increased congestive heart failure seen in one large randomized study.[28]
Vitamin K	phylloquinone, menaquinones	Fat	120 µg	Bleeding diathesis	N/D	Increases coagulation in patients taking warfarin.[29]

In nutrition and diseases

Riboflavin (Vitamin B₂)

Vitamins are essential for the normal growth and development of a multicellular organism. Using the genetic blueprint inherited from its parents, a fetus begins to develop, at the moment of conception, from the nutrients it absorbs. It requires certain vitamins and minerals to be present at certain times. These nutrients facilitate the chemical reactions that produce among other things, skin, bone, and muscle. If there is serious deficiency in one or more of these nutrients, a child may develop a deficiency disease. Even minor deficiencies may cause permanent damage.^[30]

For the most part, vitamins are obtained with food, but a few are obtained by other means. For example, microorganisms in the intestine—commonly known as "gut flora"—produce vitamin K and biotin, while one form of vitamin D is synthesized in the skin with the help of the natural ultraviolet wavelength of sunlight. Humans can produce some vitamins from precursors they consume. Examples include vitamin A, produced from beta carotene, and niacin, from the amino acid tryptophan.^[18]

Once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs that make up a multicellular organism; they also enable a multicellular life form to efficiently use chemical energy provided by food it eats, and to help process the proteins, carbohydrates, and fats required for respiration.

Deficiencies

Deficiencies of vitamins are classified as either primary or secondary. A primary deficiency occurs when an organism does not get enough of the vitamin in its food. A secondary deficiency may be due to an underlying disorder that prevents or limits the absorption or use of the vitamin, due to a “lifestyle factor”, such as smoking, excessive alcohol consumption, or the use of medications that interfere with the absorption or use of the vitamin.^[27] People who eat a varied diet are unlikely to develop a severe primary vitamin deficiency. In contrast, restrictive diets have the potential to cause prolonged vitamin deficits, which may result in often painful and potentially deadly diseases.

Because human bodies do not store most vitamins, humans must consume them regularly to avoid deficiency. Human bodily stores for different vitamins vary widely; vitamins A, D, and B₁₂ are stored in significant amounts in the human body, mainly in the liver,^[27] and an adult human's diet may be deficient in vitamins A and B₁₂ for many months before developing a deficiency condition. Vitamin B₃ is not stored in the human body in significant amounts, so stores may only last a couple of weeks.^[19][27]

Well-known human vitamin deficiencies involve thiamine (beriberi), niacin (pellagra), vitamin C (scurvy) and vitamin D (rickets). In much of the developed world, such deficiencies are rare; this is due to (1) an adequate supply of food; and (2) the addition of vitamins and minerals to common foods, often called fortification.^[18][27]

Some evidence also suggests that there is a link between vitamin deficiency and mental disorders.^[31]

Side effects and overdose

In large doses, some vitamins have documented side effects that tend to be more severe with a larger dosage. The likelihood of consuming too much of any vitamin from food is remote, but overdosing from vitamin supplementation does occur. At high enough dosages some vitamins cause side effects such as nausea, diarrhea, and vomiting.^[19][32]

When side effects emerge, recovery is often accomplished by reducing the dosage. The concentrations of vitamins an individual can tolerate vary widely, and appear to be related to age and state of health.^[33] In the United States, overdose exposure to all formulations of vitamins was reported by 62,562 individuals in 2004 (nearly 80% of these exposures were in children under the age of 6), leading to 53 "major" life-threatening outcomes and 3 deaths^[34];a small number in comparison to the 19,250 people who died of unintentional poisoning of all kinds in the U.S. in the same year (2004).^[35]

Supplements

Dietary supplements, often containing vitamins, are used to ensure that adequate amounts of nutrients are obtained on a daily basis, if optimal amounts of the nutrients cannot be obtained through a varied diet. Scientific evidence supporting the benefits of some dietary supplements is well established for certain health conditions, but others need further study.^[36] A meta-analysis in 2006 suggested that Vitamin A and E supplements not only provide no tangible health benefits for generally healthy individuals, but may actually increase mortality, although two large studies included in the analysis involved smokers, for which it was already known that beta-carotene supplements can be harmful.^[37] Another study released in May 2009 found that antioxidants such as vitamins C and E may actually curb some benefits of exercise.^[38]

In the United States, advertising for dietary supplements is required to include a disclaimer that the product is not intended to treat, diagnose, mitigate, prevent, or cure disease, and that any health claims have not been evaluated by the Food and Drug Administration.^[36] In some cases, dietary supplements may have unwanted effects, especially if taken before surgery, with other dietary supplements or medicines, or if the person taking them has certain health conditions.^[36] Vitamin supplements may also contain levels of vitamins many times higher, and in different forms, than one may ingest through food.^[39]

Intake of excessive quantities can cause vitamin poisoning, often due to overdose of Vitamin A and Vitamin D (The most common poisoning with multinutrient supplement pills does not involve a vitamin, but is rather due to the mineral iron). Due to toxicity, most common vitamins have recommended upper daily intake amounts.

Since 2005, suppliers have distinguished their products as either Medical Grade or Pharmaceutical Grade products. Both of these classifications indicate products that are manufactured to be easily absorbed by the body. Normal vitamin manufacturing is not regulated in the United States to the same standards as are medicinal pharmaceuticals, although U.S. vitamins which are manufactured for food consumption by humans or animals must be manufactured to Food Chemicals Codex (FCC), grade, commonly called "food grade".

Governmental regulation of vitamin supplements

Most countries place dietary supplements in a special category under the general umbrella of foods, not drugs. This necessitates that the manufacturer, and not the government, be responsible for ensuring that its dietary supplement products are safe before they are marketed. Unlike drug products, which must explicitly be proven safe and effective for their intended use before marketing, there are often no provisions to "approve" dietary supplements for safety or effectiveness before they reach the consumer. Maybe the biggest concern from consumers in the Baby Boom generation, especially those starting to see symptoms of aging such as arthritis, is that of convenient packaging of dietary supplements. Also unlike drug products, manufacturers and distributors of dietary supplements are not generally required to report any claims of injuries or illnesses that may be related to the use of their products.^[40][41]

Names in current and previous nomenclatures

The reason the set of vitamins seems to skip directly from E to K is that the vitamins corresponding to "letters" F-J were either reclassified over time, discarded as false leads, or renamed because of their relationship to "vitamin B", which became a "complex" of vitamins. The German-speaking scientists who isolated and described vitamin K (in addition to naming it as such) did so because the vitamin is intimately involved in the Koagulation of blood following wounding. At the time, most (but not all) of the letters from F through to J were already designated, so the use of the letter K was considered quite reasonable.

The following table lists chemicals that had previously been classified as vitamins, as well as the earlier names of vitamins that later became part of the B-complex:

Previous name[42][43]	Chemical name[42][43]	Reason for name change[42]
Vitamin B4	Adenine	DNA metabolite
Vitamin B8	Adenylic acid	DNA metabolite
Vitamin F	Essential fatty acids	Needed in large quantities (does not fit the definition of a vitamin).
Vitamin G	Riboflavin	Reclassified as Vitamin B2
Vitamin H	Biotin	Reclassified as Vitamin B7
Vitamin J	Catechol, Flavin	Protein metabolite
Vitamin L1[44]	Anthranilic acid	Protein metabolite
Vitamin L2[44]	Adenylthiomethylpentose	RNA metabolite
Vitamin M	Folic acid	Reclassified as Vitamin B9
Vitamin O	Carnitine	Protein metabolite
Vitamin P	Flavonoids	No longer classified as a vitamin
Vitamin PP	Niacin	Reclassified as Vitamin B3
Vitamin U	S-Methylmethionine	Protein metabolite

See also

Food portal

• Antioxidant
• Dietary supplement
• Dietetics
• Fat soluble vitamins
• Health freedom movement
• Illnesses related to poor nutrition
• Megavitamin therapy
• Nutrition
  • Vitamin deficiency
  • Dietary minerals
  • Essential amino acids
  • Essential nutrients
  • Nootropics
  • Nutrients
• Orthomolecular medicine
• Pharmacology
• Vitamin poisoning (overdose)
• Whole food supplements

References

1. ^ Lieberman, S, Bruning, N (1990). The Real Vitamin & Mineral Book. NY: Avery Group, 3.
2. ^ vitamin - definition of vitamin by the Free Online Dictionary, Thesaurus and Encyclopedia
3. ^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. OCLC 32308337. 
4. ^ "vitamer: Definition and Much More from Answers.com". www.answers.com. http://www.answers.com/topic/vitamer?cat=health#top. Retrieved on 2008-06-16. 
5. ^ Accessed Jan 4, 2008
6. ^ Bolander FF (2006). "Vitamins: not just for enzymes". Curr Opin Investig Drugs 7 (10): 912–5. PMID 17086936. 
7. ^ Kirk-Othmer (1984). Encyclopedia of Chemical Technology Third Edition. NY: John Wiley and Sons, Vol. 24:104.
8. ^ ^{a b c d e} Jack Challem (1997). "The Past, Present and Future of Vitamins"
9. ^ ^{a b} 1929 Nobel lecture
10. ^ Tokyo Kagaku Kaishi: (1911)
11. ^ Funk, C. and H. E. Dubin. The Vitamines. Baltimore: Williams and Wilkins Company, 1922.
12. ^ Bellis, Mary. Vitamins - Production Methods The History of the Vitamins. Retrieved 1 February 2005.
13. ^ Fukuwatari T, Shibata K (June 2008). "Urinary water-soluble vitamins and their metabolite contents as nutritional markers for evaluating vitamin intakes in young Japanese women" (^{[dead link]} – ^{Scholar search}). J. Nutr. Sci. Vitaminol. 54 (3): 223–9. doi:10.3177/jnsv.54.223. PMID 18635909. http://joi.jlc.jst.go.jp/JST.JSTAGE/jnsv/54.223?from=PubMed. 
14. ^ "Water-Soluble Vitamins". http://www.ext.colostate.edu/PUBS/FOODNUT/09312.html. Retrieved on 2008-12-07. 
15. ^ Said HM, Mohammed ZM (March 2006). "Intestinal absorption of water-soluble vitamins: an update". Curr. Opin. Gastroenterol. 22 (2): 140–6. doi:10.1097/01.mog.0000203870.22706.52. PMID 16462170. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?an=00001574-200603000-00011. 
16. ^ Maqbool A, Stallings VA (November 2008). "Update on fat-soluble vitamins in cystic fibrosis". Curr Opin Pulm Med 14 (6): 574–81. doi:10.1097/MCP.0b013e3283136787. PMID 18812835. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?an=00063198-200811000-00012. 
17. ^ Kutsky, R.J. (1973). Handbook of Vitamins and Hormones. New York:Van Nostrand Reinhold.
18. ^ ^{a b c d} Dietary Reference Intakes: Vitamins The National Academies, 2001.
19. ^ ^{a b c} Vitamin and Mineral Supplement Fact Sheets Vitamin A
20. ^ N/D= "Amount not determinable due to lack of data of adverse effects. Source of intake should be from food only to prevent high levels of intake"(see Dietary Reference Intakes: Vitamins).
21. ^ J.G. Hardman et al., eds., Goodman and Gilman's Pharmacological Basis of Therapeutics, 10th ed., p.992.
22. ^ Plain type indicates Adequate Intakes (A/I). "The AI is believed to cover the needs of all individuals, but a lack of data prevent being able to specify with confidence the percentage of individuals covered by this intake" (see Dietary Reference Intakes: Vitamins).
23. ^ Vitamin and Mineral Supplement Fact Sheets Vitamin B₆
24. ^ Vitamin and Mineral Supplement Fact Sheets Vitamin B₁₂
25. ^ http://dietary-supplements.info.nih.gov/factsheets/vitaminb12.asp
26. ^ Value represents suggested intake without adequate sunlight exposure (see Dietary Reference Intakes: Vitamins).
27. ^ ^{a b c d e} The Merck Manual: Nutritional Disorders: Vitamin Introduction Please select specific vitamins from the list at the top of the page.
28. ^ http://findarticles.com/p/articles/mi_m0ISW/is_262/ai_n13675725,
29. ^ Rohde LE, de Assis MC, Rabelo ER (January 2007). "Dietary vitamin K intake and anticoagulation in elderly patients". Curr Opin Clin Nutr Metab Care 10 (1): 1–5. doi:10.1097/MCO.0b013e328011c46c. PMID 17143047. 
30. ^ Dr. Leonid A. Gavrilov, Pieces of the Puzzle: Aging Research Today and Tomorrow
31. ^ Lakhan SE; Vieira KF. Nutritional therapies for mental disorders. Nutrition Journal 2008;7(2).
32. ^ Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academy Press, Washington, DC, 2001.
33. ^ Healthier Kids Section: What to take and how to take it.
34. ^ 2004 Annual Report of the American Association of Poison Control Centers Toxic Exposure Surveillance System.
35. ^ National Center for Health Statistics
36. ^ ^{a b c} Use and Safety of Dietary Supplements NIH office of Dietary Supplements.
37. ^ Bjelakovic G, et al. (2007). "Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis". JAMA 297 (8): 842–57. doi:10.1001/jama.297.8.842. PMID 17327526. . See also the letter to JAMA by Philip Taylor and Sanford Dawsey and the reply by the authors of the original paper.
38. ^ http://www.nytimes.com/2009/05/12/health/research/12exer.html?em=&pagewanted=print
39. ^ Jane Higdon Vitamin E recommendations at Linus Pauling Institute's Micronutrient Information Center
40. ^ Overview of Dietary Supplements
41. ^ Illnesses and Injuries Associated with the Use of Selected Dietary Supplements U. S. FDA Center for Food Safety and Applied Nutrition
42. ^ ^{a b c} Every Vitamin Page All Vitamins and Pseudo-Vitamins. Compiled by David Bennett.
43. ^ ^{a b} Vitamins and minerals - names and facts
44. ^ ^{a b} Michael W. Davidson (2004) Anthranilic Acid (Vitamin L) Florida State University. Accessed 20-02-07

External links

• USDA RDA chart in PDF format
• Health Canada Dietary Reference Intakes Reference Chart for Vitamins
• NIH Office of Dietary Supplements: Fact Sheets
• NIH Office of Dietary Supplements. Dietary Supplements: Background Information

v • d • e Vitamins (A11) Fat soluble A Retinol · β-Carotene · Tretinoin · α-Carotene D D2 (Ergosterol, Ergocalciferol)  · D3 (7-Dehydrocholesterol, Previtamin D3, Cholecalciferol, 25-hydroxycholecalciferol, Calcitriol (1,25-dihydroxycholecalciferol), Calcitroic acid) D4 (Dihydroergocalciferol)  · D5  · D analogues (Dihydrotachysterol, Calcipotriol, Tacalcitol, Paricalcitol) E Tocopherol (Alpha, Beta, Gamma, Delta) · Tocotrienol · Tocofersolan K Naphthoquinone · Phylloquinone/K1 · Menatetrenone/K2 · Menadione/K3 Water soluble B B1 (Thiamine, Sulbutiamine) · B2 (Riboflavin) · B3 (Niacin, Nicotinamide) · B5 (Pantothenic acid, Dexpanthenol, Pantethine) · B6 (Pyridoxine, Pyridoxal phosphate, Pyridoxamine) B7 (Biotin) · B9 (Folic acid, Dihydrofolic acid, Folinic acid) · B12 (Cyanocobalamin, Hydroxocobalamin, Methylcobalamin, Cobamamide)  · Choline C Ascorbic acid  · Dehydroascorbic acid see also: enzyme cofactors, enzymes

v • d • e Food chemistry Additives · Carbohydrates · Coloring · Enzymes · Essential fatty acids · Flavors · Lipids · Minerals · Proteins · Vitamins · Water

v • d • e Nutrition disorders (E40-68, 260-269) Hypoalimentation/ malnutrition Protein-energy malnutrition Kwashiorkor · Marasmus · Catabolysis Avitaminosis B vitamins B1: Beriberi/Wernicke's encephalopathy(Thiamine deficiency) · B2: Ariboflavinosis · B3: Pellagra(Niacin deficiency) · B6: Pyridoxine deficiency · B7: Biotin deficiency · B9: Folate deficiency · B12: Vitamin B12 deficiency Other vitamins A: Vitamin A deficiency/Bitot's spots · C: Scurvy · D: Rickets/Osteomalacia · E: Vitamin E deficiency · K: Vitamin K deficiency Mineral deficiency Zinc · Iron · Magnesium · Chromium · Selenium (Keshan disease) · Manganese · Molybdenum · Copper · Calcium · Potassium Hyperalimentation Overweight · Obesity Childhood obesity · Obesity hypoventilation syndrome Vitamin poisoning Hypervitaminosis A · Hypervitaminosis D · Hypervitaminosis E Mineral overload see inborn errors of metal metabolism, toxicity

v • d • e Dietary supplements Types Amino acids • Bodybuilding supplement • Energy drink • Energy bar • Fatty acids • Herbal Supplements • Minerals • Prebiotics • Probiotics (Lactobacillus, Bifidobacterium) • Vitamins • Whole food supplements, effervescent Vitamins and minerals Retinol (Vitamin A) • B vitamins: Thiamine (B1) • Riboflavin (B2) • Niacin (B3) • Pantothenic acid (B5) • Pyridoxine (B6) • Biotin (B7) • Folic acid (B9) • Cyanocobalamin (B12) • Ascorbic acid (Vitamin C) • Ergocalciferol and Cholecalciferol (Vitamin D) • Tocopherol (Vitamin E) • Naphthoquinone (Vitamin K) • Calcium • Choline • Chlorine • Chromium • Cobalt • Copper • Fluorine • Iodine • Iron • Magnesium • Manganese • Molybdenum • Phosphorus • Potassium • Selenium • Sodium • Sulfur • Zinc Other common ingredients Carnitine • Chondroitin sulfate • Cod liver oil • Copper gluconate • Creatine/Creatine supplements • Dietary fiber • Elemental calcium • Ephedra • Fish oil • Folic acid • Ginseng • Glucosamine • Glutamine • Iron supplements • Japanese Honeysuckle • Krill oil • Lingzhi • Linseed oil • Melatonin • Red yeast rice • Royal jelly • Saw palmetto • Spirulina • Taurine • Wheatgrass • Wolfberry • Yohimbine • Zinc gluconate Related articles Codex Alimentarius • Enzyte • Metabolife • Hadacol • Nutraceutical • Multivitamin • Nutrition

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n. - vitamin

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Deutsch (German)
n. - Vitamin

Ελληνική (Greek)
n. - (βιοχημ.) βιταμίνη

Italiano (Italian)
vitamina

Português (Portuguese)
n. - vitamina (f) (Bioq.)

Русский (Russian)
витамин

Español (Spanish)
n. - vitamina

Svenska (Swedish)
n. - vitamin

中文（简体）(Chinese (Simplified))
维他命, 维生素

中文（繁體）(Chinese (Traditional))
n. - 維他命, 維生素

한국어 (Korean)
n. - 비타민

日本語 (Japanese)
n. - ビタミン

العربيه (Arabic)
‏(الاسم) فيتامين, حيمين‏

עברית (Hebrew)
n. - ‮תערובת אורגנית החיונית ליצורים חיים רבים כדי לחיות ולהתפתח, ויטמין‬

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