Consequences of revised estimates of carotenoid bioefficacy for dietary control of vitamin A deficiency in developing countries.

According to existing recommendations of the Food and Agriculture Organization (FAO)/World Health Organization (WHO), the amount of provitamin A in a mixed diet having the same vitamin A activity as 1 microg of retinol is 6 microg of beta-carotene or 12 microg of other provitamin A carotenoids. The efficiency of this conversion is referred to as bioefficacy. Recently, using data from healthy people in developed countries and based on a two-step process, the U.S. Institute of Medicine (IOM) derived new conversion factors. The first step established the bioefficacy of beta-carotene in oil at 2 microg having the same vitamin A activity as 1 microg of retinol; the second step established the bioavailability of beta-carotene in foods relative to that of beta-carotene in oil at 1:6. Thus, 2 microg of beta-carotene in oil or 12 microg of beta-carotene in mixed foods has the same vitamin A activity as 1 microg of retinol. Based on existing FAO food balance sheets and the FAO/WHO conversion rates, all populations should be able to meet their vitamin A requirements from existing dietary sources. However, using the new IOM conversion rates, populations in developing countries could not achieve adequacy. Additionally, field studies suggest that, instead of 12 microg, 21 microg of beta-carotene has the same vitamin A activity as 1 microg of retinol, which implies that effective vitamin A intake is even lower. Therefore, controlling vitamin A deficiency in developing countries requires not only vitamin A supplementation but also food-based approaches, including food fortification, and possibly the introduction of new strains of plants with enhanced vitamin A activity.