The role of provitamin A carotenoids in the prevention and control of vitamin A deficiency.

That beta-carotene is the main source of vitamin A in fruits and vegetables has been known for many years. Many studies have been conducted to assess bioconversion of beta-carotene to vitamin A in animals. More recently, bioconversion studies using stable-isotopically labeled beta-carotene have been used to assess bioconversion in humans. The efficiency of the bioconversion of beta-carotene to vitamin A has been accepted to be six but this value may vary depending on vitamin A status and the amount of beta-carotene consumed. This paper reviews the human studies on purified beta-carotene supplements and/or consumption of fruits and vegetables conducted to ascertain whether beta-carotene can alter the vitamin A status of deficient populations. The conclusion is that data are lacking from well-designed studies to show that, with the possible exception of red palm oil, beta-carotene-rich foods are as effective as vitamin A supplements for eliminating vitamin A deficiency. Nevertheless, the data do show that beta-carotene-rich foods may be important for preventing vitamin A deficiency.