Vitamin A is one of the most versatile vitamins, playing roles in several important body processes. The best known vitamin A benefits relates to vision. For a person to see, light reaching the eye must be transformed into nerve impulses that the brain interprets to produce visual images. The transformers are molecules of pigment in the cells of the retina, a paper-thin tissue lining the back of the eye. A portion of each pigment molecule is retinal, a compound the body can synthesize only if vitamin A is supplied by the diet in some form. Thus, when vitamin A is deficient, vision is impaired. Specifically, the eye has difficulty adapting to changing light levels. For a person deficient in vitamin A, a flash of bright light at night (after the eye has adapted to darkness) is followed by a prolonged spell of night blindness. Because night blindness is easy to diagnose, it aids in the diagnosis of vitamin A deficiency. (Night blindness is only a symptom, however, and it may indicate a condition other than vitamin A deficiency.)
One of the best vitamin A benefits are it helps to maintain healthy epithelial tissue: skin and the cells (called epithelial cells) lining such body cavities as the small intestine and lungs. Vitamin A is also involved in the production of sperm, the normal development of fetuses, the immune response, hearing, taste, and growth.
As much as a year’s supply of vitamin A can be stored in the body (90 percent of it in the liver). If you stop eating good food sources of vitamin A, deficiency symptoms will not begin to appear until your stores are depleted. Then, however, the consequences are profound, and include blindness and reduced resistance to infection. Although vitamin A deficiency is rarely seen in developed countries such as the United States and Canada, it is a serious public health problem in developing countries, where millions of children suffer from blindness, infections, and the other consequences of vitamin A deficiencies.
Vitamin A toxicity, in contrast, is not nearly as widespread as deficiency. Nevertheless, it can also lead to severe health consequences, including joint pain, dryness of skin, hair loss, irritability, fatigue, headaches, weakness, nausea, and liver damage. Thus, it’s especially important not to take mega doses of this nutrient even it has a good vitamin A benefits for the body.
Although toxicity poses a hazard to people who take supplements of preformed vitamin A, toxicity poses virtually no risk to people who obtain vitamin A from foods in the form of beta-carotene.
Sources of Vitamin A in Foods The major sources of vitamin A (in the form of beta-carotene) are almost all brightly colored, in hues of green, yellow, orange, and red which are the best vitamin A benefits for the body. Any plant food with significant vitamin A activity must have some color, because beta-carotene is a rich, deep-yellow, almost orange color. (Preformed vitamin A is pale yellow.) The dark-green leafy vegetables contain large amounts of the green pigment chlorophyll, which masks the carotene in them.