Vitamin A, or retinol, is one of the fat-soluble vitamins consisting of a family of compounds called retinoids. Although ancient Egyptians recognized that eating liver would help cure night blindness, it wasn't until 1913 that vitamin A was recognized as having the same biological activity as retinol. Retinol had been isolated from the retina and was the subject of studies of sight, night vision and particular types of vision problems.
In 1984, vitamin A deficiency was recognized as a major cause of infant mortality in developing countries. A worldwide campaign to cut mortality rates began in 1997 to make vitamin A supplements available to malnourished children in these areas.
Food Sources
Animal protein contains vitamin A, and is a major dietary source. Besides meat and fish, vitamin A is found in egg yolks, milk, cheese and organ meats, especially liver. Plants don't contain vitamin A, but many fruits and vegetables do contain carotenoids, which your body uses to manufacture vitamin A. Beta carotene is a major carotenoid found leafy dark green vegetables and orange and yellow fruits and vegetables, including cantaloupe, apricots, carrots, pumpkin, sweet potatoes, broccoli and spinach.
Symptoms
Lack of vitamin A can cause night blindness, dry eye and other visual impairments. In malnourished children, the youngest are the most severely affected. An ocular examination often flags a potential deficiency, and a simple blood test can verify vitamin A levels. Vitamin A, or retinol, is stored in the liver. While adults in developing countries have liver stores of vitamin A to draw from during periods of famine, children's livers have not had a chance to store retinol and they can be rapidly affected by malnutrition.
Immunity
The immune system requires vitamin A to function properly. Major infectious diseases are more severe and more difficult to treat if vitamin A deficiency interferes with normal immune responses. In such cases, vitamin A supplements can help strengthen immune responses. Children with vitamin A deficiency who develop complications to measles respond to vitamin A supplementation. Vitamin A can lower their mortality risk by diminishing the severe symptoms and shortening the duration of the disease.
Bone Growth
Vitamin A is necessary for the proper functioning of osteoblasts and osteoclasts, the specialized cells that build healthy bones. Not only can a vitamin A deficiency cause malformed bone tissue, it can bring about secondary issues, such as problems with nervous system development if the skull is the affected bone.
References
- Drugs.com; Vitamin A; Alison Evert, MS, RD, CDE, et al.; February 8, 2011
- Merck Manuals Online Medical Library; Vitamin A; Larry E. Johnson, MD, PhD; April 2007
- DSM: Vitamin Basics: History of Vitamin A
- "Current Drug Targets, Inflammation and Allergy"; Osteoblasts and Osteoclasts in Bone Remodeling and Inflammation; Y. Tanaka, et al.; June 2005
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