Dictionary:

zinc

  (zĭngk)

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A bluish-white, lustrous metallic element that is brittle at room temperature but malleable with heating. It is used to form a wide variety of alloys including brass, bronze, various solders, and nickel silver, in galvanizing iron and other metals, for electric fuses, anodes, and meter cases, and in roofing, gutters, and various household objects. Atomic number 30; atomic weight 65.39; melting point 419.4°C; boiling point 907°C; specific gravity 7.133 (25°C); valence 2.

To coat or treat with zinc; galvanize.

[German Zink, possibly from Zinke, spike (so called because it becomes jagged in the furnace), from Middle High German zinke, from Old High German zinko.]

Background

Zinc is an elemental metal. It is listed on the Periodic Table as "Zn," with an atomic number of 30 and an atomic weight of 65.37, and it melts at 788°F (420°C). Zinc is usually a gray metallic color, but it can be polished to a shiny silver luster. In nature, it is only found as a chemical compound, not as pure zinc, and can be used as a raw material for castings and coatings.

During the era of the Roman Empire, people used zinc to alloy copper into brass for weapons. In this crude process, the zinc was captured by the copper during the heating of the ores, though little was realized at the time about the importance of zinc in metallurgy. The name zinc may be derived from the German word "zinn," which means tin. The scientific discovery of zinc is credited to Nadreas Sigismund Marggraf, a German chemist who isolated pure zinc in 1746. The first production facility, or smelter, was founded in Bristol, England by William Champion shortly thereafter.

Only about 5% of the world's zinc supply is mined in the United States, with the balance coming primarily from India, Mexico, and Canada. Approximately 6.7 million metric tons of zinc ore are produced worldwide. Roughly two thirds of the zinc used in the United States is imported.

Applications

Zinc is primarily used for galvanizing steel against corrosion, die casting of intricate machine parts, and in batteries and other electrical applications. Zinc is also alloyed with copper to form brass.

Galvanizing steel involves applying a thin coating of zinc to all exposed surfaces of the steel to guard against corrosion. Zinc offers excellent corrosion resistance because it is more easily oxidized by the atmosphere. Oxidation occurs when metal is exposed to air or water, and electrons from the metal transfer to the oxygen. When zinc is tightly bonded to steel, the zinc frees up its electrons more readily than the steel, leaving the stronger metal beneath intact. The application of the zinc coating is accomplished by dipping the steel into molten zinc or by electrolytic plating of the steel with zinc, much like chrome plating.

Die-casting alloys typically contain 96% zinc and 4% aluminum. The die-casting process uses a two-piece steel die and a casting press to hold the die halves together during injection of the molten metal. Inside the steel die is a cavity that has the negative image of the part to be cast. The molten metal is injected into the cavity under pressure, accurately filling the entire void. The metal cools, and the press opens the die halves, revealing the formed part. The zinc cast parts are very close to the desired shape, requiring little machining before they are placed into an assembly. Typical applications include copier, aircraft, and medical instrument parts. Automobile makers use zinc die castings for emblems, moldings, door handles, and brackets. Zinc die castings are easily chrome plated for durability and appearance.

One unique application of zinc takes particular advantage of its ability to transfer its corrosion resistance properties by electrical contact. This application is called a "sacrificial anode." The anodes, made of almost pure zinc, are bolted to aluminum marine engines. During operation in water, especially salt water, the oxidation forms a weak electrical current, which may corrode the hull and engine parts. Since zinc is easily oxidized in the presence of this electrical current, it "sacrifices" itself by corroding quickly, consuming all of the electrical imbalance in the ship. The remaining aluminum hull and engine are not corroded as a result. As it is consumed, the anode must be replaced to assure continued protection.

In an application similar to the sacrificial anode, zinc is used as a component in battery production. The dry cell battery creates a chemical reaction with zinc in a metal housing (or "can") that results in a voltage potential between two connections. An electrical device, such as a flashlight or portable radio, can be connected to the battery and powered by the electricity produced. Thus connected, the reaction maintains the electrical current for the duration of the available chemical reactants.

Zinc as a compound is used in pharmaceuticals, rubber, cosmetics, paint, and ceramic glaze. Other compounds use zinc in cathode-ray tubes, soldering flux, and wood preservatives.

The Manufacturing
Process

Mining

• Zinc ores are dug from underground mines using conventional blasting, drilling, and hauling techniques. The ores occur as zinc sulfide (also called sphalerite), zinc carbonate (smithsonite), zinc silicate (calimine), and in compounds of manganese and iron (franklinite). Zinc ore is sometimes mined in conjunction with silver or lead ores. In addition to the ore itself, oil and sulfuric acid are required for the breakdown of the ores; and electricity, coke, or natural gas are needed to provide the heat energy for smelting.

Froth flotation

• Zinc can be produced by a process called froth flotation, which is also used for reduction of copper and lead ores. This process involves grinding the zinc ore to a fine powder, mixing it with water, pine oil, and flotation chemicals, and then agitating the mixture to "float" the zinc to the surface. A variety of chemicals are used to coat the important zinc particles and prevent them from becoming wetted by the water. Then air is injected, and the coated minerals attach themselves to the bubbles. The operation is performed inside a vat and agitated with an impeller. The rotating impeller draws the air down the standpipe that surrounds the impeller shaft and dissipates it throughout the mixture or "pulp." The zinc rises to the top and the residue stays in the bottom of the pulp, since it cannot adhere to the bubbles. Automatic scrapers remove the mineral-laden froth containing the zinc.

Filtering

• The froth is filtered to remove the water and liquid oils. The paste-like remainder is mixed with lime and sent to a furnace. The furnace roasts the mixture at 2500°F (1371°C), which fuses the minerals into solid chunks called sinter. At this point, the material has been completely converted to zinc oxide.

Smelting

• The next reduction process uses a blast furnace to melt the prepared ore into its elemental components. The blast furnace is fueled by electricity, coke, or natural gas, which generate temperatures of up to 2200°F (1204°C). This, however, also generates carbon dioxide, which recombines with the zinc as it cools to re-form zinc oxide. To reduce this reformation, the zinc is sprayed with molten lead while it is still hot. The lead, at 1022°F (550°C), dissolves the zinc and carries it to another chamber, where it is cooled to 824°F (440°C). At this temperature, the lighter zinc separates out of the lead and is drained off the top. The lead is reheated and returned to the blast furnace.

Refining

• Further metal improvement can be made by keeping the zinc molten and undisturbed for several hours. In this state, iron and other contaminants settle to the bottom, allowing the almost pure zinc to be carefully drawn off the top and cast into ingots.

Alloying

• Most zinc is alloyed with other metals before use to improve its properties. Alloying involves remelting and mixing the zinc with other metals in precise proportions. For example, approximately 4% aluminum is added to improve casting quality and die life in the die-casting process. Other added alloys are small amounts of titanium, copper, and magnesium. After alloying, the molten metal is poured into sow molds and ingot molds. Sows can weigh several thousand pounds, while ingots weigh about 45 pounds (20 kg).

Quality Control

Metal alloys are inspected by a process called spectrographic analysis. The metal is burned under a protective cover using an electrical arc. The light emitted by the burning metal is passed though an apparatus much like a prism, which breaks the light into all of its individual colors. Every element has a different set of colors, or spectrum, which is like a fingerprint. Any foreign material will alter the spectrum, and in doing so show its unique color spectrum, identifying it. The computer in the spectrograph uses sensors to pick up these colors. The computer program then produces a printout that identifies each element in the spectrum and the concentration within the metal. Elements can be reduced or increased to alter the composition.

The Future

Because of the strength to weight ratio of zinc, its use by the automotive industry as a die casting has been diminishing in the past few years. Magnesium, aluminum, and plastics have taken over many zinc applications. The use of zinc to galvanize automobile body parts has been increasing, however. Many vehicles today are protected by zinc galvanizing which allows the manufacturer to offer extended warranties for body rust problems with new cars.

Where To Learn More

Periodicals

Queneau, Paul B. and Jerome P. Downey. "Secondary Zinc Production Minimizes Waste." Pollution Engineering, November 1994, pp. 42-44.

Yates, Edward M. "Zinc: Major Mine Production Cuts in 1993." Engineering and Mining Journal, March 1994, pp. 19-21.

[Article by: Douglas E. Betts]

A chemical element, Zn, atomic number 30, and atomic weight 65.38. Zinc is a malleable, ductile, gray metal. Because of chemical similarities among zinc, cadmium, and mercury, these three metals are classed together in a transition-elements subgroup of the periodic table. See also Metal; Periodic table; Transition elements.

Fifteen isotopes of zinc are known, of which five are stable, having atomic masses of 64, 66, 67, 68, and 70. About half of ordinary zinc occurs as the isotope of atomic mass 64. The half-lives of the radioactive isotopes range from 88 s for ⁶¹Zn to 244 days for ⁶⁵Zn.

Zinc is a fairly active metal chemically. It can be ignited with some difficulty to give a blue-green flame in air and to discharge clouds of zinc oxide smoke. Zinc ranks above hydrogen in the electrochemical series, so that metallic zinc in an acidic solution will react to liberate hydrogen gas as the zinc passes into solution to form dipositively charged zinc ions, Zn²⁺. This reaction is slow with very pure zinc, but the presence of small amounts of impurities, addition of a trace of copper sulfate, or contact between the zinc surface and such metals as nickel or platinum facilitates formation of gaseous hydrogen and speeds the reaction. The combination of zinc and dilute acid is often used to generate small quantities of hydrogen in the laboratory. Zinc also dissolves in strongly alkaline solutions, such as sodium hydroxide, to liberate hydrogen and form dinegatively charged tetrahydroxozincate ions, Zn(OH)₄²⁻, sometimes written as ZnO₂²⁻ in the formulas of the zincate compounds. Zinc also dissolves in solutions of ammonia or ammonium salts. The common soluble zinc compounds undergo to some extent the process of hydrolysis, which makes their solutions slightly acidic. The ion Zn²⁺ is colorless, so that the relatively few zinc compounds that are not colorless in large crystals, or white as powders, receive their color through the influence of the other constituents. Some of the atomic and ionic properties of zinc are shown in the table. See also Electrochemical series; Hydrolysis.

Zinc also forms many coordination compounds. The zincates are actually coordination compounds, or complexes, in which hydroxide ions, OH⁻, are bound to the zinc ions. Ammonia, NH₃, forms complexes with zinc, such as the typical tetrammine zinc ion, [Zn(NH₃)₄]²⁺. Zinc cyanide, usually given the simple formula Zn(CN)₂, is a coordination compound in which many alternating zinc and cyanide ions are three-dimensionally bound together in a very large molecule. This compound is still widely used in zinc plating, but concern over environmental pollution has led to increasing use of zinc chloride plating baths. In most coordination compounds of zinc, the fundamental structural unit is a central zinc ion surrounded by four coordinated groups arranged spatially at the corners of a regular tetrahedron. See also Coordination chemistry; Coordination complexes.

Pure, freshly polished zinc is bluish-white, lustrous, and moderately hard (2.5 on Mohs scale). Moist air brings about a superficial tarnish to give the metal its usual grayish color. Pure zinc is malleable and ductile enough to be rolled or drawn, but small amounts of other metals present as contaminants may render it brittle. Malleability of even pure zinc is improved by heating zinc to 100–150°C (212–300°F). If heated zinc is mechanically worked; it does not embrittle on cooling. Zinc melts at 420°C (788°F) and boils at 907°C (1665°F). Its density is 7.13 times that of water, so that 1 ft³ (0.028 m³) of zinc weighs 445 lb (200 kg).

As a conductor of heat and of electricity, zinc ranks fairly high. However, its electrical resistivity (5.92 microhm-cm at 20°C or 68°F) is almost four times that of silver, the best conductor. As a conductor of heat, zinc is likewise only about one-fourth as efficient as silver. At 0.91 K zinc is an electrical superconductor. Pure zinc is not ferromagnetic, but the alloy compound ZrZn₂ displays ferromagnetism below 35 K.

The most important uses of zinc are in its alloys and as a protective coating on other metals. Coating iron or steel with zinc is known as galvanizing, and it may be done by immersing the article in melted zinc (hot-dip process), depositing zinc electrolytically onto the article in a plating bath (electrogalvanizing), exposing the article to powdered zinc near its melting point (sherardizing), or spraying the article with melted zinc (metallizing). The mere physical presence of the zinc coat prevents corrosion of iron, and even if breaks in the coat expose portions of the iron, the greater chemical activity of the zinc causes it to be consumed in preference to the iron. Adding small amounts of other metals to galvanizing baths has been found to improve the adhesion and weathering qualities of the coating. See also Electroplating of metals; Galvanizing.

Even such nonstructural materials as cardboard can be zinc-coated by low-temperature flame spraying. Other important uses of zinc are in brass and zinc die-casting alloys, in zinc sheet and strip, in electrical dry cells, in making certain zinc compounds, and as a reducing agent in chemical preparations.

A so-called tumble-plating process coats small metal parts by applying zinc powder to them with an adhesive, then tumbling them with glass beads to roll out the powder into a continuous coat of zinc. Rechargeable nickel-zinc batteries offer higher energy densities than conventional dry cells. Foamed zinc metal has been suggested for use in lightweight structures such as aircraft and spacecraft. Some other uses of zinc are in dry cells, roofing, lithographic plates, fuses, organ pipes, and wire coatings. Zinc dust, a flammable material when dry, is used in fireworks and as a chemical catalyst and reducing agent. Radioactive ⁶⁵Zn is used medically in the study of metabolism of zinc, and also in determining rates of wear for zinc-containing alloys. See also Metal coatings; Zinc alloys.

Zinc is believed to be needed for normal growth and development of all living species, including humans; actually, life without zinc would be impossible. Zinc is a common element that is present in virtually every type of human food, and zinc deficiency is therefore not considered to be a common problem in humans. Zinc is a trace element; that is, it is present in biological fluids at a concentration below 1 ppm, and only a small amount (normally <25 mg) is required in the daily diet. (The recommended daily allowance for zinc is 15 mg/day for adults and 10 mg/day for growing children.) It is relatively nontoxic, without noticeable side effects at intake levels of up to 10 times the normal daily requirement.

An essential mineral which forms the prosthetic group of a large number of enzymes, and also the receptor proteins for steroid and thyroid hormones and vitamin A and vitamin D. Deficiency results in hypogonadism and delayed puberty, small stature, and mild anaemia; it occurs mainly in subtropical regions where a great deal of zinc is lost in sweat, and the diet is largely based on unleavened wholemeal bread, in which much of the zinc is unavailable because of the high content of phytate.

Meat, fish (especially shellfish), legumes, and (leavened) wholegrain cereals are rich sources. Synergistic zinc is a trade name for zinc supplement that also contains copper and vitamin A, which are claimed to aid its absorption.

An essential trace element that works in close association with vitamins and over 100 enzymes. It is, therefore, involved in almost every physiological function in the body. It forms part of a protein (gustin) in saliva and plays a role in taste and smell. It also helps to heal wounds. Although there is only a little evidence that taking extra zinc can improve athletic performance, some weight-lifters take zinc supplements in the belief that it increases stamina by prolonging muscle contractions.

Zinc deficiency may cause loss of taste and smell, and a reduction of appetite. A deficiency can slow down the healing of wounds (zinc oxide ointment is applied to abrasions to accelerate healing), retard growth in children, and reduce the sperm count of adult males (the concentration of zinc in semen is 100 times greater than in the blood plasma).

The US recommended dietary allowance (RDA) for adults is 15 mg for males and 12 mg for females. The UK Reference Nutrient Intake for adults is 9.5 mg for males and 7.0 mg for females (lactating mothers require higher amounts). Zinc can be obtained from seafood (especially oysters and other shellfish), cereal crops, legumes, wheat germ, and yeast products. Zinc may bind to some constituents of dietary fibre, interfering with its absorption from the gut. Consequently, vegetarians may require a higher than normal intake of this element. As zinc is lost in urine and sweat, exercisers (especially those who train intensively) may also need zinc supplementation. However, zinc supplementation should not exceed the RDA because excessive amounts can have harmful effects including inhibition of copper absorption, which may lead to anaemia.

A bluish-white chemical element used in medicine in the form of various salts and as a component in some silver amalgams.

Description

Zinc is a mineral that is essential for a healthy immune system, production of certain hormones, wound healing, bone formation, and clear skin. It is required in very small amounts, and is thus known as a trace mineral. Despite the low requirement, zinc is found in nearly every cell of the body and is a key to the proper function of more than 300 enzymes, including superoxide dismutase. Normal growth and development cannot occur without it.

General Use

The U.S. Recommended Dietary Allowance (RDA) for zinc is 5 milligrams (mg) for children under one year of age, 10 mg for children aged one to 10 years old, 15 mg for males 11 years or older, 12 mg for females 11 years or older, 15 mg for women who are pregnant, and 16-19 mg for women who are lactating.

Zinc has become a popular remedy for the common cold. Evidence shows that it is unlikely to prevent upper respiratory infections, but beginning a supplement promptly when symptoms occur can significantly shorten the duration of the illness. The only form of zinc proven effective for this purpose is the zinc gluconate or zinc acetate lozenge. Formulations of 13-23 mg or more appear to be most effective, and need to be dissolved in the mouth in order to exert antiviral properties. Swallowing or sucking on oral zinc tablets will not work. The lozenges can be used every two hours for up to a week or two at most.

People who are deficient in zinc are prone to getting more frequent and longer lasting infections of various types. Zinc acts as an immune booster, in part due to stimulation of the thymus gland. This gland tends to shrink with age, and consequently produces less of the hormones that boost the production of infection-fighting white blood cells. Supplemental zinc, at one to two times RDA amounts, can reverse this tendency and improve immune function.

In another immune stimulant capacity, zinc can offer some relief from chronic infections with Candida albicans, or yeast. Most women will experience a vaginal yeast infection at some time, and are particularly prone to them during the childbearing years. Some individuals appear to be more susceptible than others. One study showed yeast-fighting benefits for zinc even for those who were not deficient in the mineral to begin with. Other supplements that will complement zinc in combating yeast problems are vitamin A, vitamin C, and vitamin E. Another measure that can help to limit problems with Candida is eating yogurt, which is an excellent source of Lactobacillus, a friendly bacteria that competes with yeast. Limiting sweets in the diet and eating garlic or odor-free garlic supplements may also prove helpful.

People who are going to have surgery are well advised to make sure they are getting the RDA of zinc, vitamin A, and vitamin C in order to optimize wound healing. A deficiency of any of these nutrients can significantly lengthen the time it takes to heal. Adequate levels of these vitamins and minerals for at least a few weeks before and after surgery can speed healing. The same nutrients are important to minimize the healing time of bedsores, burns, and other skin lesions.

There are two male health problems that can potentially benefit from zinc supplementation. Testosterone is one of the hormones that requires zinc for production. Men with infertility as a result of low testosterone levels may experience improvement from taking a zinc supplement. Another common condition that zinc can be helpful for is benign prostatic hypertrophy, a common cause of abnormally frequent urination in older men. Taking an extra 50 mg a day for three to six months offers symptomatic relief for some men.

Teenagers are often low in zinc, and also tend to experience more acne than the general population. The doses used in studies have been in the high range, requiring medical supervision, but increasing dietary zinc or taking a modest supplement in order to get the RDA amount is low risk and may prove helpful for those suffering from acne. People should consult a knowledgeable health care provider before taking large doses of any supplement.

There is some evidence that zinc supplementation may slightly relieve the symptoms of rheumatoid arthritis, but the studies are not yet conclusive. It's possible that those who initially had low zinc levels benefited the most.

In 2002, new research showed certain concentrations of zinc improved the effect of a therapy called interferon for some patients with chronic hepatitis C. Although the trial was preliminary, it showed promise for further research into zinc's effects in enhancing interferon therapy.

Zinc is sometimes promoted as an aid for memory. This may be true to the extent that vitamin B₆ and neurotransmitters are not properly utilized without it. However, in the case of people with Alzheimer's disease, zinc can cause more harm than good. Some experiments indicate that zinc actually decreases intellectual function of people with this disease. Under these circumstances, it is probably best to stick to the RDA of 15 mg as a maximum daily amount of zinc.

The frequency of sickle-cell crisis in patients with sickle-cell anemia may be decreased by zinc supplementation. The decrease was significant in one study, although the severity of the attacks that occurred was not affected. Use of zinc supplementation or other treatment for sicklecell anemia, a serious condition, should not be undertaken without the supervision of a health care provider.

Both the retina of the eye, and the cochlea in the inner ear contain large amounts of zinc, which they appear to need in order to function properly. Dr. George E. Shambaugh, Jr., M.D., is a professor emeritus of otolaryngology and head and neck surgery at Northwestern University Medical School in Chicago. In Prevention's Healing with Vitamins, he "estimates that about 25% of the people he sees with severe tinnitus are zinc-deficient." He adds that they sometimes have other symptoms of zinc deficiency. Large doses may be used in order to provide relief for this problem. Medical supervision and monitoring are necessary to undertake this course of treatment.

Topical zinc can be useful for some conditions, including cold sores. It is also available in a combination formula with the antibiotic erythromycin for the treatment of acne. Zinc oxide is a commonly used ingredient in the strongest sun block preparations and some creams for the treatment of diaper rash and superficial skin injuries. Men can use topical zinc oxide to speed the healing of genital herpes lesions, but it is too drying for women to use in the vaginal area.

There is still not enough information on some of the claims that are made for zinc. A few that may have merit are the prevention or slowing of macular degeneration, and relieving psoriasis. One should consult a health care provider for these uses.

Deficiency

It is not uncommon to have mild to moderately low levels of zinc, although serious deficiency is rare. Symptoms can include an increased susceptibility to infection, rashes, hair loss, poor growth in children, delayed healing of wounds, rashes, acne, male infertility, poor appetite, decreased sense of taste and smell, and possible swelling of the mouth, tongue, and eyelids.

A more serious, chronic deficiency can cause severe growth problems, including dwarfism and poor bone maturation. The spleen and liver may become enlarged. Testicular size and function both tend to decrease. Cataracts may form in the eyes, the optic nerve can become swollen, and color vision is sometimes affected by a profound lack of zinc. Hearing is sometimes affected as well.

Since meats are the best sources of zinc, strict vegetarians and vegans are among the groups more likely to be deficient. The absorption of zinc is inhibited by high fiber foods, so people who have diets that are very high in whole grain and fiber need to take supplements separately from the fiber. Zinc is needed in larger amounts for women who are pregnant or breastfeeding. Deficiency during pregnancy may lower fetal birthweight, as well as increase maternal risk of toxemia. A good prenatal vitamin is likely to contain an adequate amount. People over age 50 don't absorb zinc as well, nor do they generally have adequate intake, and may require a supplement. Alcoholics generally have poor nutritional status to begin with, and alcohol also depletes stored zinc.

There is an increased need for most vitamins and minerals for people who are chronically under high stress. Those who have had surgery, severe burns, wasting illnesses, or poor nutrition may require larger amounts of zinc than average.

Some diseases increase the risk of zinc deficiency. Sickle-cell anemia, diabetes, and kidney disease can all affect zinc metabolism. People with Crohn's disease, sprue, chronic diarrhea, or babies with acrodermatitis enteropathica also have an increased need for zinc. Consult a health care provider for appropriate supplementation instructions.

Preparations

Natural Sources

Oysters are tremendously high in zinc. Some sources, such as whole grains, beans, and nuts, have good zinc content but the fiber in these foods prevents it from being absorbed well. Foods with better utilized zinc include beef, chicken, turkey, milk, cheese, and yogurt. Pure maple syrup also is a good source of zinc.

Supplemental Sources

Zinc supplements are available as oral tablets in various forms, as well as lozenges. Zinc gluconate is the type most commonly used in lozenge form to kill upper respiratory viruses. One should select brands that do not use citric acid or tartaric acid for flavoring, as these appear to impair the effectiveness. The best-absorbed oral types of zinc may include zinc citrate, zinc acetate, or zinc picolinate. Zinc sulfate is the most likely to cause stomach irritation. Topical formulations are used for acne and skin injuries. Oral zinc should not be taken with foods that will reduce its absorption, such as coffee, bran, protein, phytates, calcium, or phosphorus. Supplements should be stored in a cool, dry location, away from direct light, and out of the reach of children.

Precautions

Toxicity can occur with excessively large doses of zinc supplements, and produce symptoms, including fever, cough, abdominal pain, nausea, vomiting, diarrhea, drowsiness, restlessness, and gait abnormalities. If doses greater than 100 mg per day are taken chronically, it can result in anemia, immune insufficiency, heart problems, and copper deficiency. High doses of zinc can also cause a decrease in high density lipoprotein (HDL), or good, cholesterol.

People who have hemochromatosis, are allergic to zinc, or are infected with HIV should not take supplemental zinc. Ulcers in the stomach or duodenum may be aggravated by supplements as well. Those with glaucoma should use caution if using eye drops containing zinc. Overuse of supplemental zinc during pregnancy can increase the risk of premature birth and stillbirth, particularly if the supplement is taken in the third trimester. This increase in adverse outcomes has been documented with zinc dosages of 100 mg taken three times daily.

Side Effects

Zinc may cause irritation of the stomach, and is best taken with food in order to avoid nausea. The lozenge form used to treat colds has a strong taste, and can alter the sense of taste and smell for up to a few days.

Interactions

The absorption of vitamin A is improved by zinc supplements, but they may interfere with the absorption of other minerals taken at the same time, including calcium, magnesium, iron, and copper. Supplements of calcium, magnesium, and copper should be taken at different times than the zinc. Iron should only be taken if a known deficiency exists. Thiazide and loop diuretic medications, sometimes used for people with high blood pressure, congestive heart failure, or liver disease, increase the loss of zinc. Levels are also lowered by oral contraceptives. Zinc can decrease the absorption of tetracycline and quinolone class antibiotics, antacids, soy, or manganese, and should not be taken at the same time of day. Drinking coffee at the same time as taking zinc can reduce the absorption by as much as half. Even moderate amounts of alcohol impair zinc metabolism and increase its excretion. Chelation with EDTA can deplete zinc, so patients undergoing chelation need to supplement with zinc, according to the instructions of the health care provider.

Resources

Books

Bratman, Steven and David Kroll. Natural Health Bible. California: Prima Publishing, 1999.

Feinstein, Alice. Prevention's Healing with Vitamins. Pennsylvania: Rodale Press, 1996.

Griffith, H. Winter. Vitamins, Herbs, Minerals & supplements: the complete guide. Arizona: Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's letter/Prescriber's Letter Natural Medicines Comprehensive Database. California: Therapeutic Research Faculty, 1999.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: alpha books, 1997.

Periodicals

Vernarec, Emil. "Zinc May Enhance the Efficacy of Interferon." RN (May 2002): 28.

[Article by: Judith Turner; Teresa G. Odle]

For more information on zinc, visit Britannica.com.

A hard bluish white metal, brittle at normal temperatures, very malleable and ductile when heated; not subject to corrosion; used for galvanizing sheet steel and iron, in various metal alloys, and as an oxide for white paint pigment.

An essential trace element that works in close association with vitamins and over 100 enzymes. It is, therefore, involved in almost every physiological function in the body. It forms part of a protein (gustin) in saliva and plays a role in taste and smell. It helps the A and B vitamins to function effectively, and is thought to increase resistance against cold and some other infections. It also helps to heal wounds. Zinc deficiency may cause loss of taste and smell, and a reduction of appetite. A deficiency can slow down the healing of wounds (zinc oxide ointment is applied to abrasions to accelerate healing), retard growth in children, and reduce the sperm count of adult males (the concentration of zinc in semen is 100 times greater than in the blood plasma). Zinc can be obtained from seafood (especially oysters and other shellfish), cereal crops, legumes, wheat germ, and yeast products. Zinc may bind to some constituents of dietary fibre, interfering with its absorption from the gut. Consequently, vegetarians may require a higher than normal intake of this element. As zinc is lost in urine and sweat, exercisers (especially those who train intensively) may also need zinc supplementation. However, zinc supplementation should not exceed the RDA because excessive amounts can have harmful effects including inhibition of copper absorption, which may lead to anaemia.

A chemical element, atomic number 30, atomic weight 65.37, symbol Zn.
Zinc is a trace element that is a component of several enzymes, including DNA and RNA polymerases, and carbonic anhydrase. Zinc salts are used in skin lotions, eye washes, the treatment and prevention of footrot of sheep and facial eczema of sheep and cattle.

• z. acetate — a salt used as an astringent and styptic.
• z. cadmium sulfide — used in the preparation of fluoroscopic screens; is fluorescent and emits yellow-green light when excited by x-rays.
• z. carbonate — a mild astringent; used mainly as calamine.
• z. chromate — an industrial compound used in cold galvanizing of metal. Accidental access causes diarrhea and fatal enteritis.
• z. finger motif — sequence of approximately 30 amino acids, forming a helix-turn-helix, believed to form a structure that includes tetrahedrally coordinated zinc (II) ions. Found in many eukaryotic, prokaryotic and viral DNA-binding proteins.
• z. finger protein — DNA-binding proteins that contain zinc-finger motifs.
• z. gelatin — a mixture of zinc oxide, gelatin, glycerin and purified water; used topically as a protectant.
• z. gluconate — a source of supplementary zinc.
• hereditary z. deficiency — lethal trait A46; see inherited parakeratosis.
• z. nutritional deficiency — causes parakeratosis in pigs, a chronic, afebrile, noninflammatory disease of the epidermis characterized by crusty proliferation and cracking of the skin. Dogs fed diets with high levels of calcium or cereals may have poor absorption of zinc and develop signs of deficiency, primarily in the skin. See also zinc-responsive dermatosis.
• z. ointment — a preparation of zinc oxide and mineral oil in white ointment; used topically as an astringent and protectant.
• z. oversupplementation — causes hemolytic anemia, anorexia and vomiting.
• z. oxide — a compound used as a topical astringent and protectant. Inhalation of fumes causes interstitial emphysema and atelectasis.
• z. phosphate — used as a phosphate-bonded cement in restorative dentistry.
• z. phosphide — used at one time as a rodenticide. When ingested the poisonous gas phosphine is liberated and kills the animal without diagnostic signs or lesions.
• z. poisoning — is usually chronic and causes stiffness and lameness with particular involvement of the shoulder joint in which there is a degenerative arthritis. In acute poisoning there is gastroenteritis with vomiting.
• z.-responsive dermatoses — see parakeratosis, zinc-responsive dermatosis.
• z. stearate — a compound of zinc with stearic and palmitic acids; used as a water-repellent protective powder in dermatoses.
• z. sulfate — a compound used as an ophthalmic astringent, in skin lotions (see white lotion), for sheep footrot, and the treatment of facial eczema. It is the common form of zinc for oral supplementation and treatment of zinc-responsive diseases.
• z. sulfate flotation test — used to demonstrate nematode eggs, protozoan cysts, and larvae in feces and bronchial secretions.
• z. sulfate turbidity test — 1. serum globulins are precipitated by zinc sulfate. The test is used for the semiquantitative assessment of the immunological status of foals and calves when there is a question of whether they have suckled to receive immunoglubulins.
— 2. an outdated liver function test.
• z. undecylenate — a compound used topically in 20% ointment as an antifungal agent. See also undecylenic acid.