Radio Ad, Vitamin “A” Explanation

       The average person (e.g. 75 Kg man) needs about 900 micrograms (mcg) of vitamin A, provided it’s the correct form or complex.  That’s 12 mcg/kg. And it’s about 3000 IU (international units).

       Some “mega-vitamins" are made which are for the most part excessive and unnecessary, but most normal vitamins supply about 3000 IU give or take 500 IU. 2000 IU is an adequate American food supplement. In fact most of us probably get an adequate amount of vitamin A from our normal every day diets.

       The type, form or vitamin A complex is important. Immediately usable sources of Vitamin A are esters that are converted to an alcohol, retinol, in the intestine.

     Usable vitamin A is a complex of fat soluble compounds called retinoids. Certain animal fats such as those from milk and eggs are good sources of vitamin A. The very best source of Vitamin A is liver. Animal fat is a must for efficient vitamin A absorption in humans. It is interesting that the livers of many arctic mammals (husky, polar bear, seal, walrus) have vitamin A concentrations so high toxicity is a risk. 

       Carrots, pumpkins, broccoli and other plants are sources of provitamin A compounds called carotenoids. They must be converted to retinoids in the intestine. It was once thought that one could not overdose on water miscible vitamin A compounds. Recent studies suggest this is probably not the case. In fact water miscible vitamin A may be even more inclined to cause hypervitaminosis.

     This is not to say that if you are a vegetarian that you cannot get adequate vitamin A, but it is something which needs considerable thought and you may need the advice of a doctor or dietitian.

     10,000 IU/day of preformed vitamin A can be taken safely, but this is approaching a maximum amount for the average person, especially if taken for long periods. If you are wanting an intake at the upper end, 5,000 IU is plenty adequate and keeps you well below the toxic level.

Dan David, O.D.