Function:
Vitamin A is a fat-soluble vitamin. It is a name used for a large number of chemicals known as retinoids. Retinol and retinal are considered to be the types of vitamin A used in the body. It is needed for proper vision, the formation and maintenance of skin, mucous membranes, bones, gene expression, red blood cell formation, reproduction, growth and development, and immune function.

Recommended Dietary Allowance:
900 mcg (2,910 IU) per day for men and 700 mcg (2,310 IU) per day for women.

Deficiency:
Inadequate vitamin A results in vision impairment, especially night blindness. Up to 500,000 children in developing countries go blind each year because of vitamin A deficiency which causes severe drying of the eyes. Other symptoms of deficiency include excessive skin dryness, and lack of mucous secretion causing susceptibility to all infectious diseases.

Sources:
Vitamin A is present in organ meats, dairy products, eggs, fish liver oil, and from provitamin A carotenoids. Ten provitamin A carotenoids are present in certain orange, red, green, and dark-yellow fruits and vegetables. They are referred to as provitamin A carotenoids because they can be converted in the body to an active form of vitamin A as needed. Alpha-carotene, beta-carotene, and beta-cryptoxanthin are the most important carotenoids with beta-carotene the most active.

THE STANDARD OF MEASURE FOR VITAMIN A IS RETINOL ACTIVITY EQUIVALENCY (RAE).

This demonstrates the fact that synthetic beta-carotene (in oil) is half as potent as retinol for vitamin A activity, but it is 6 times more potent than beta-carotene in food and 12 times more potent than other carotenoids in food. Individuals taking synthetic beta-carotene in the past have shown no protection from disease. In fact in smokers the risk of lung cancer may be higher. Perhaps this potency has an effect of blocking other beneficial plant chemicals in fruits and vegetables.

Toxicity and UL:
Excess vitamin A intake has been shown to increase the risk of birth defects, liver abnormalities, osteoporosis, dry skin, and in infants and young children bulging of the skull . Eating seal and polar bear liver, which have high vitamin A content, has resulted in severe illness sometimes with coma and death. Pregnant women or those anticipating pregnancy should carefully avoid intakes higher than the RDA and not use vitamin A containing skin preparations. Retinoids are very long acting with side effects and birth defects sometimes occurring months after discontinuing therapy. The UL for vitamin A is 3,000 mcg (10,000 IU), per day.

Recommendation:
The needs for this nutrient can be met by choosing foods rich in provitamin A carotenoids and vitamin A.

If a supplement is desired, provitamin A carotenoids from natural sources such as the alga D. salina are available and provide a safe way meet vitamin A needs. If vitamin A stored in the body is adequate provitamin A compounds will not convert to vitamin A and toxicity will not occur.

Supplementation with vitamin A higher than the RDA levels is strongly discouraged. Synthetic beta-carotene should be avoided.

For more information visit:
http://osu.orst.edu/dept/lpi/infocenter/vitamins/vitaminA/