NIJMEGEN, THE NETHERLANDS. Vitamin A (retinol) is a fat-soluble vitamin required to ensure proper function of the immune system and to counteract the development of night blindness and weak eyesight; it may also play an important role in cancer prevention.
The current Recommended Daily Allowance (RDA) in North America is 5000 IU or, more correctly, 1000 RE equivalents for men and 4000 IU or 800 RE for women. Children need between 400 and 700 RE daily depending on age. Any intake above the daily requirement is stored in the liver. This fact has led to cautions about taking too much vitamin A as it can be toxic in large quantities. Vitamin A toxicity may occur in adults who take more than 10,000 RE daily for several years. Pregnant women should keep their daily intake below 1000 RE/day.
Vitamin A is obtained from the diet in two forms either as retinol (from animal products) or in the form of carotenes (from fruits and vegetables) which the body converts to retinol. In 1967 the World Health Organization reported that it took six micrograms of beta-carotene to produce one microgram (1 RE) of pure vitamin A. This conversion factor has been used ever since to determine the average daily vitamin A intake throughout the world.
Using the WHO factor it was estimated that the average daily vitamin A intake varied from about 600 RE in South America and Asia to about 1000 RE in Europe and North America. In other words, it's adequate in Europe and North America, but deficient in Asia and South America.
Dutch and Indonesian researchers now report that the 1967 WHO conversion factor is seriously wrong. Using up-to-date analysis techniques and new information about bioavailability and bioconversion of vitamin A and carotenes they conclude that it takes not six micrograms of beta-carotene from fruits and vegetables to yield one microgram of vitamin A, but rather 21 micrograms. This finding puts a completely different complexion on things.
Essentially, the entire world is likely to be vitamin A deficient. The revised estimated daily intake of vitamin A is now only 780 RE in Europe, 581 RE in North America, 372 RE in South America, and a mere 258 RE in Asia where blindness among children is becoming endemic.
The researchers urge further work to determine how to tackle this massive problem.
Editor's Note: This project obviously could take years. In the meantime it would seem wise to supplement with cod or halibut liver oil which are both excellent sources of vitamins A and D.
West, Clive E. Meeting requirements for vitamin A. Nutrition Reviews, Vol. 58, November 2000, pp. 341- 45
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