Plant sources of provitamin A and human nutriture.

Hypovitaminosis A is a problem in many parts of the developing world. Beyond the stop-gap measures of capsule distribution and food fortification, increased consumption of accessible sources of vitamin A, specifically of the carotenoid provitamin A in yellow, orange, and green plants, has been promoted as the sustainable, long-term solution. However, a search of the available literature reveals few examples of human studies to support the effectiveness of this solution. Evidence from feeding studies shows an almost universally poorer uptake of intact carotenoids from plant sources as opposed to pure, chemical sources. With notable exceptions, the bioconversion of plant carotenoids to preformed vitamin A also seems to be inefficient. Epidemiologic observations in poor Third World populations and in vegetarians in an industrialized nation indicate a relatively greater potency for animal sources of vitamin A. In developing countries, low fat intakes, intestinal roundworms, recurrent diarrhea, and tropical enteropathy all may contribute to reduced utilization of plant provitamin A. The accepted 6:1 equivalency of beta-carotene to preformed vitamin A must be challenged and reexamined in the context of dietary plants. The consequences of operating on a miscalculation could be serious indeed for public health programs designed to alleviate and eradicate hypovitaminosis A.