Vitamin A deficiency

Vitamin A deficiency
Classification and external resources
Retinol
ICD-10	E50.9
ICD-9	264.9
DiseasesDB	13902
eMedicine	med/2381
MeSH	D014802

Vitamin A deficiency is a lack of vitamin A in humans. It is common in developing countries but rarely seen in developed countries. Night blindness is one of the first signs of vitamin A deficiency. Complete blindness can also occur due to retinal injury - Vitamin A has a major role in phototransduction. Approximately 250,000 to 500,000 malnourished children in the developing world go blind each year from a deficiency of vitamin A, approximately half of which die within a year of becoming blind. The United Nations Special Session on Children in 2002 set the elimination of vitamin A deficiency by 2010. The prevalence of night blindness due to vitamin A deficiency is also high among pregnant women in many developing countries. Vitamin A deficiency also contributes to maternal mortality and other poor outcomes in pregnancy and lactation.^[1][2][3][4]

Vitamin A deficiency also diminishes the ability to fight infections. In countries where children are not immunized, infectious disease like measles have higher fatality rates. As elucidated by Dr. Alfred Sommer, even mild, subclinical deficiency can also be a problem, as it may increase children's risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness.

Signs and symptoms

The most common cause of blindness in developing countries is vitamin A deficiency (VAD). The World Health Organization (WHO) estimates 13.8 million children to have some degree of visual loss related to VAD. ^[5] Night blindness and its worsened condition, xerophthalmia, are markers of VAD, as VAD can also lead to impaired immune function, cancer, and birth defects.

Night blindness is the difficulty for the eyes to adjust to dim light. Affected individuals are unable to distinguish images in low levels of illumination. People with night blindness have poor vision in the darkness, but see normally when adequate light is present.

VAD affects vision by inhibiting the production of rhodopsin, the eye pigment responsible for sensing low light situations. Rhodopsin is found in the retina and is composed of retinal (an active form of vitamin A) and opsin (a protein). Because the body cannot create retinal in sufficient amounts, a diet low in vitamin A will lead to a decreased amount of rhodopsin in the eye, as there is inadequate retinal to bind with opsin. Night blindness results.

Night blindness caused by VAD has been associated with the loss of goblet cells in the conjunctiva, a membrane covering the outer surface of the eye. Goblet cells are responsible for secretion of mucus, and their absence results in xerophthalmia, a condition where the eyes fail to produce tears. Dead epithelial and microbial cells accumulate on the conjunctiva and form debris that can lead to infection and possibly blindness.^[6]

Decreasing night blindness requires the improvement of vitamin A status in at risk populations. Supplements and fortification of food have been shown to be effective interventions. Supplement treatment for night blindness includes high doses of vitamin A (200,000 IU) in the form of retinyl palmitate to be taken by mouth, which is administered two to four times a year.^[7] Intramuscular injections are poorly absorbed and are ineffective in delivering sufficient bio-available vitamin A. Fortification of food with vitamin A is costly, but can be done in wheat, sugar, and milk.^[8] Households may circumvent expensive fortified food by altering dietary habits. Consumption of yellow-orange fruits and vegetables rich in carotenoids, specifically beta carotene, provides pro-vitamin A precursors that will prevent VAD related night blindness.

Causes

Prevalence of vitamin A deficiency. Source: WHO

The major cause is diets which include few animal sources of pre-formed vitamin A. Breast milk of a lactating mother with vitamin A deficiency contains little vitamin A, which provides a breast-fed child with too little vitamin A.^[9]

In addition to dietary problems, there are other causes of vitamin A deficiency. Iron deficiency can affect vitamin A uptake. Excess alcohol consumption can deplete vitamin A, and a stressed liver may be more susceptible to vitamin A toxicity. People who consume large amounts of alcohol should seek medical advice before taking vitamin A supplements. In general, people should also seek medical advice before taking vitamin A supplements if they have any condition associated with fat malabsorption such as pancreatitis, cystic fibrosis, tropical sprue & biliary obstruction.

Treatment

Treatment of vitamin A deficiency can be undertaken with both oral and injectable forms, generally as vitamin A palmitate.

• As an oral form, the supplementation of vitamin A is effective for lowering the risk of morbidity, especially from severe diarrhea, and reducing mortality from measles and all-cause mortality. Some countries where vitamin A deficiency is a public health problem address its elimination by including vitamin A supplements available in capsule form with National Immunization Days (NIDs) for polio eradication or measles. Vitamin A capsules cost about US$0.02. The capsules are easy to handle; they don’t need to be stored in a refrigerator or vaccine carrier. When the correct dosage is given, vitamin A is safe and has no negative effect on seroconversion rates for Oral Polio Vaccine or measles vaccine. However, because the benefit of vitamin A supplements is transient, children need them regularly every four to six months. Since NIDs provide only one dose per year, NIDs-linked vitamin A distribution must be complemented by other dose programs to maintain vitamin A in children^[10][11] Maternal high supplementation benefits both mother and breast-fed infant: high dose vitamin A supplementation of the lactating mother in the first month postpartum can provide the breast-fed infant with an appropriate amount of vitamin A through breast milk. However, high-dose supplementation of pregnant women should be avoided because it can cause miscarriage and birth defects.^[12]

Some non-profit, non-governmental organizations have taken on the task of Vitamin A deficiency prevention as well. One such organization is Vitamin Angels. Vitamin Angels has committed itself to eradicating childhood blindness due to Vitamin A deficiency on the planet by the year 2020. Operation 20/20 was launched in 2007 and will cover 18 countries. The program gives children two high dose vitamin A and anti-parasitic supplements (twice a year for four years), which provides children with enough of the nutrient during their most vulnerable years in order to prevent them from going blind and suffering from other life-threatening diseases caused by Vitamin A Deficiency. [1]

• Food fortification is also useful for improving vitamin A deficiency. A variety of oily and dry forms of the retinol esters, retinyl acetates and retinyl palmitate are available for food fortification of vitamin A. Margarine and oil are the ideal food vehicles for vitamin A fortification. They protect vitamin A from oxidation during storage and prompt absorption of vitamin A. β-carotene and retinyl acetate or retinyl palmitate are used as a form of vitamin A for vitamin A fortification of fat-based foods. Fortification of sugar with retinyl palmitate as a form of vitamin A has been used extensively throughout Central America. Cereal flours, milk powder, and liquid milk are also used as food vehicles for vitamin A fortification.^[13][14]

• Dietary diversification can also control vitamin A deficiency. Non-animal sources of vitamin A which contain pre-formed vitamin A account for greater than 80% of intake for most individuals in the developing world. The increase in consumption of vitamin A-rich foods of animal origin in addition to fruits and vegetables has beneficial effects on vitamin A deficiency.^[15]

Epidemiology

Disability-adjusted life year for vitamin A deficiency per 100,000 inhabitants in 2002.^[16]

     no data      less than 35      35-70      70-105      105-140      140-175      175-210      210-245      245-280      280-315      315-350      350-400      more than 400

See also

• Retinol

References

1. ^ "WHO Vitamin A deficiency". http://www.who.int/nutrition/topics/vad/en/. Retrieved 2008-03-03. 
2. ^ Latham, Michael E. (1997). Human Nutrition in the Developing World (Fao Food and Nutrition Paper). Food & Agriculture Organization of the United. ISBN 92-5-103818-X. 
3. ^ Sommer, Alfred (1995). Vitamin a Deficiency and Its Consequences: A Field Guide to Detection and Control. Geneva: World Health Organization. ISBN 92-4-154478-3. 
4. ^ "A world fit for children". http://www.unicef.org/worldfitforchildren/files/A-RES-S27-2E.pdf. Retrieved 2008-03-03. 
5. ^ J S Rahi, S Sripathi, C E Gilbert, A Foster. Childhood blindness due to vitamin A deficiency in India: regional variations. Archives of Disease in Childhood. 72: 330-333, 1995.
6. ^ Underwood, Barbara A. Vitamin A Deficiency Disorders: International Efforts to Control A Preventable “Pox.” J. Nutr. 134: 231S–236S, 2004.
7. ^ Sommer A, Muhilal, Tarwotjo I, Djunaedi E and Glover J (1980b) Oral versus intramuscular vitamin A in the treatment of xerophthalmia. Lancet 1: 557–559.
8. ^ Arroyave G, Mejia LA and Aguilar JR (1981) The effect of vitamin A fortification of sugar on the serum vitamin A levels of preschool Guatemalan children: a longitudinal evaluation. J. Nutr. 34: 41–49.
9. ^ "SLTop". http://www.sightandlife.org/activity/maps/mapsE/MapWorld.html. Retrieved 2008-03-14. 
10. ^ "Distribution of vitamin A during national immunization days". http://www.who.int/vaccines-documents/DocsPDF/www9836.pdf. Retrieved 2008-03-03. 
11. ^ "WHO Vitamin A supplementation". http://www.who.int/vaccines/en/vitamina.shtml. Retrieved 2008-03-03. 
12. ^ Stoltzfus RJ, Hakimi M, Miller KW, et al. (1993). "High dose vitamin A supplementation of breast-feeding Indonesian mothers: effects on the vitamin A status of mother and infant". J. Nutr. 123 (4): 666–75. PMID 8463867. 
13. ^ edited by Lindsay Allen ... (2006). Guidelines on Food Fortification With Micronutrients. Geneva: World Health Organization. ISBN 92-4-159401-2. 
14. ^ Food and Agriculture Organization of the United Nations (1996). Food Fortification: Tech & Quality Control (Food & Nutrition Papers). Bernan Assoc. ISBN 9251038848. 
15. ^ "childinfo.org: Vitamin A Deficiency". http://www.childinfo.org/areas/vitamina/. Retrieved 2008-03-14. 
16. ^ "Mortality and Burden of Disease Estimates for WHO Member States in 2002" (xls). World Health Organization. 2002. http://www.who.int/entity/healthinfo/statistics/bodgbddeathdalyestimates.xls.