Vitamin A
Vital for healthy eyes, Vitamin A is luckily found in plenty of food sources including animal protein, dairy products, and fresh fruits and vegetables.
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Many vitamins were first identified as key to good health in the early 1900s. Vitamin A, originally identified as “fat soluble factor A,” was actually identified sometime after the discovery of Vitamin B, known as “water soluble factor B.” But these two names started the tradition of labeling each newly identified vitamin with the next letter of the alphabet.
One of the most vital roles Vitamin A plays is with respect to vision. Named “retinol” because of its presence in the retina, the alcohol is metabolized to the light-absorbing aldehyde, retinal, which is essential for both color vision and for night vision.
There are generally two forms of Vitamin A available in the diet. Foods such as milk and liver that come from animals contain preformed Vitamin A, which is the more readily used form of the vitamin. Highly colored fruits and vegetables such as cantaloupe, carrots, sweet potatoes, broccoli and spinach contain carotenoids, which are provitamins; of these substances, beta-carotene is converted most efficiently into the active Vitamin A.
Nearly one third of children around the world under the age of five lack sufficient Vitamin A, primarily as they do not get enough fresh fruits, vegetables, protein and dairy products in their diet. Night blindness, the inability to see in limited light, is one of the first symptoms of a lack of Vitamin A.
Conversely, because Vitamin A is fat soluble, it is easily stored in the body and not as easily removed as the water soluble B and C vitamins. As a result, it is possible to take in too much Vitamin A, resulting in numerous unpleasant health effects. When it comes to this particular nutrient, as Mary Poppins would say, “Enough is as good as a feast.”
More information about Vitamin A can be found at http://www.nlm.nih.gov/medlineplus/ency/article/002400.htm