Vitamin A deficiency. New knowledge on diagnosis, consequences and therapy.

Due to the rapid development of biochemical analyses in the last 10 years different substances like vitamin A, with an apparent clarified metabolism and action, were re-estimated. As a result, new knowledge was presented which could be essential for human health. Some details and consequences are reviewed in this paper. Marginal deficiency, which also may occur in industrialized nations, cannot be determined with certainty by usual blood analyses. The reasons for marginal deficiency are either different diseases or unbalanced nutrition. From epidemiological research it is argued that low vitamin A intake is associated with a higher incidence of cancer in different tissues. However, vitamin A may lead by over-dosing to toxic side effects. There exists a possibility that vitamin A is teratogenic also in humans. Thus, for safety reasons, woman who can become pregnant should not be advised to supplement the vitamin more than twice the RDA of the US Food and Nutrition Board for pregnant women (10,000 I.U./day) if there is no clear-cut indication. On the other hand there are indications that malformations may also caused by vitamin A deficiency.