Vitamin A is a fat-soluble vitamin that is responsible for vision; and forming and maintaining healthy skin, teeth, skeletal and soft tissue and mucous membranes in your body. As a general group, the discovery of vitamins began in the early 1900s when Polish scientist Casimir Funk discovered an anti-beriberi substance isolated from rice polishings. Funk gave it the name "vitamine" because it was an amine and necessary for life. The "e" on the end of vitamine was later dropped, resulting in the name "vitamin," because only a few of these essential substances were found to be amines.
Discovery of Vitamin A
In 1917 vitamin A was discovered independently by Elmer McCollum at the University of Wisconsin-Madison and Lafayette Mendell and Thomas Burr Osborne of Yale University. McCollum extracted a factor from butter that he called "fat-soluble A" to distinguish it from the water-soluble anti-beriberi substance Funk had discovered. There are two forms of vitamin A: retinol, the fully preformed vitamin A; and carotenoids, which are pigments found in plants that your body converts to vitamin A.
Retinols
The chemical name retinol was given to vitamin A due to its major function in the retina of the eye. Retinol is the preformed vitamin A found in foods of animal origin. Retinol is the active form of vitamin A and can be formed into the derivatives retinal and retinoic acid in your body. Retinol is an essential part of rhodopsin, the light-sensitive pigment in the eye that allows your eyes to adjust to different amounts of available light.
Carotenoids
The carotenoids, known as provitamin A, are dark-colored dyes or pigments found in plant foods. Beta carotene is the most common of the over 500 carotenoids. Most, but not all, carotenoids can be converted into vitamin A. As a group, the carotenoids are powerful antioxidants that protect your body from the damage of free radicals. Free radicals contribute to chronic diseases and the aging process. The National Institutes of Health states food sources of carotenoids may reduce the risk of cancers, but supplemental beta carotene does not appear to contribute to further reduction of this risk.
RDA and Food Sources
The recommended dietary allowance for vitamin A in a healthy adult man or woman over the age of 18 is 900 mcg per day, and 700 mcg per day, respectively. The retinol form of vitamin A can be found in foods of animal origin such as beef liver, dairy and fish including tuna, salmon and herring. You can find carotenoids in yellow and orange fruits and vegetables as well as dark leafy green vegetables and broccoli.
References
- "Advanced Nutrition and Human Metabolism, Third Edition" ; James L. Groff, et al; 2000
- "Basic Nutrition and Diet Therapy"; Sue Rodwell Williams; 2001
- USDA National Agricultural Library; DRI Tables
- National Library of Medicine; National Institutes of Health; Vitamin A
- News Medical; Vitamin A History
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