Vitamin A (retinoid) is a fat-soluble vitamin found mainly in animal foods in the vitamin form and in plant foods primarily as carotenes, substances that are formed into vitamin A chiefly in the small intestine.

Function: Essential for growth and for keeping skin and other tissues healthy; helps eyes to adapt to dim light and perceive colors; essential for normal tooth development.

Sources: Beef, chicken and pork livers; whole and vitamin A-fortified milk; cheddar cheese; butter; margarine; egg yolk; deep green, yellow or orange vegetables and fruits (including carrots, spinach, collards, broccoli, kale, nectarines, apricots, mangoes, cantaloupe, pumpkins, winter squash, turnip greens, sweet potatoes, and watermelon).

Deficiency: Vitamin A deficiency is reare in the United States; it mainly occurs among some people in developing countries. Some signs include skin changes, stunted growth, night blindness, and serious eye problems (such as drying, thickening, wrinkling, and muddy pigmentation of the mucous membrane lining the eyelid and eyeball, which eventually can destroy the eye). Inadequate intakes of foods containing vitamin A have been associated with some types of cancer, but the effect, if any, appears related to lack of carotene.

Excess: Because vitamin A is fat soluble, it is stored in the body. As a result, continued high doses (several times the U.S. RDA) have toxic effects. Signs of toxicity include dry and itching skin, headaches, and nausea and diarrhea. High vitamin A intake during pregnancy also may cause birth defects, but it is not known at what level this can occur. Excessive amounts of carotene are not known to be toxic, but will cause the skin to turn deep yellow. The color disappears when the amount of carotene in the diet is decreased.