Rather than a single vitamin, vitamin A is actually a family of related chemicals that are closely associated with optimum health. In the body, these chemicals are converted into nutrients that may help protect vision, regulate gene expression, strengthen the immune system and perform a number of other vital functions.
Vitamin A & The Prevention of Night Blindness
In the human eye, the retina is responsible for converting light into the nerve impulses that the brain interprets as vision. If the rod cells of the retina do not get appropriate amounts of vitamin A, their ability to absorb light is impaired. Scientists call this condition “impaired dark adaptation” but you know it simply as “night blindness”.
If vitamin A deficiency is severe enough, or continues for an extended length of time, permanent damage to the conjunctiva and corneas can result. In fact, vitamin A deficiency (and the damage it causes to the eyes) is the leading cause of blindness in children growing up in developing countries.
Vitamin A & Immunity
Researchers know that children who are only mildly deficient in vitamin A are at higher risks for asthma, diarrhea and other childhood ailments. They’re also more likely to die from infections like measles than children getting appropriate amounts of vitamin A in their diets.
Vitamin A is vital for immunity in adults, too. One study found that expectant mothers with HIV were up to four times more likely to pass the infection on to their unborn children if the mothers were vitamin A deficient.
Vitamin A & Cancer
Can vitamin A lower your susceptibility of certain types of cancer? Researchers think so. While the scientific evidence is presently scant, a few in vitro studies have suggested that vitamin A may reduce the growth of breast cancer cells.
How Much Vitamin A Do You Need?
Vitamin A is absolutely vital to good health but too much vitamin A is also associated with birth defects, an increased risk of lung cancer and a condition doctors call hypervitaminosis A. Because the body doesn’t rid itself of excess vitamin A easily, excessive doses of the nutrient can build up in the body and lead to nausea, headaches, dry skin even a buildup of fluid in the brain.
Today, the Recommended Daily Allowance of vitamin A is 300 mcg for infants and preschoolers, 400 mcg for children and up to 600 mcg for pre-teens. The specific recommendation for teens and adults varies and ranges from 700 to 1300 mcg.
References:
Office of Dietary Supplements. (2006). Dietary Supplement Fact Sheet: Vitamin A and Carotenoids.
Higdon, J. (2003). Vitamin A.