VITAMIN A

           

               VITAMIN A

          

               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.