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Vitamin A Deficiency

Vitamin A refers to the fat-soluble retinol compound that is essential for various biological functions. Retinaldehydes and retinoic acids are biologically active derivatives from retinol. 11-cis retinaldehyde is an essential form of vitamin A that is required for normal vision. Retinoic acid is essential for normal cell morphogenesis, growth, and differentiation. Vitamin A is also needed for iron utilization and normal immunity. Deficiency of vitamin A can lead to visual impairment and skin lesions. However, they can be effectively treated with appropriate levels of the vitamin.

Dietary Sources and Epidemiology

Vitamin A can be derived from metabolites of carotenoids. In nature, carotene is the most prevalent carotenoid in the food supply. Liver and fish are excellent sources of preformed vitamin A. Sources of pro-vitamin A carotenoids include dark green and dark-colored vegetables and fruits. Developing infants and children are at most risk for vitamin A deficiency because breast and cow milk contain low levels of vitamin A.

In developing countries vitamin A deficiency is one of the common causes of blindness, affecting more than a quarter of a million children each year with a 50 percent mortality rate within the year. Increased mortality in children is due primarily from infectious diseases, measles, respiratory diseases, and diarrhea. In the United States, vitamin A deficiency is typically due to diseases associated with malabsorption of fat such as celiac sprue. Because 90 percent of absorbed vitamin A is stored in the liver, zinc deficiency can also interfere with the release of vitamin A from storage. Chronic alcoholism can also cause deficiency because alcohol competes for alcohol dehydrogenase, a key enzyme required for the conversion of retinol to retinaldehyde in the eye. Other causes of deficiency include interference from drugs such as neomycin and mineral oil laxative abuse.

Clinical Symptoms and Treatment

Patients often present to their doctors complaining of difficulty in seeing in the dark (night blindness). This is due to low levels of 11-cis retinaldehyde, an important molecule required for dark adaptation of vision. Other symptoms of deficiency include dryness of the conjunctiva (xerosis), corneal ulcers and necrosis (keratomalacia), hyperkeratotic skin lesions (increased keratinization of the epithelium), and development of small white patches on the conjunctiva (Bitot's spots). Normal range of serum vitamin A level is 30–65 mg/dL. Serum levels below the norm are commonly seen in advanced stages of deficiency.

Night blindness, poor wound healing, and other signs of deficiency can be effectively treated with appropriate levels of vitamin A. Excessive levels of vitamin A should be avoided as the vitamin is fat soluble and can accumulate in the body, leading to symptoms of vitamin A toxicity and can lead to congenital malformations in women who are pregnant.

  • vitamin deficiency
  • Vitamin A deficiency
  • vitamins
Andrew J.Waskey, Dalton State College
http://dx.doi.org/10.4135/9781412963855.n1222
See Also:

Bibliography

A. CatharineRoss, “Retinoid Production and Catabolism: Role of Diet in Regulating Retinol Esterification and Retinoic Acid Oxidation,”Journal of Nutrition (v.133/1, 2003)
A. CatharineRoss, “Vitamin A Supplementation as Therapy—Are the Benefits Disease Specific?”American Journal of Clinical Nutrition (v.68/1, 1998)
“Vitamin A Deficiency,”e-Medicine, http://www.emedicine.com/med/topic2381.htm (cited February 2007).
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