The ABC's of the RDA
Working in Iran and Egypt in the early 1960s, two physicians named James Halsted and Ananda Prasad examined a group of young men who were sexually underdeveloped and extremely small for their age. Through a series of studies, the doctors concluded that the young men were suffering from extreme zinc deficiency. They gave them zinc supplements, and, amazingly, the youths began to grow and their genitals developed normally.
Halsted and Prasad concluded that the problem stemmed from the young men's diet, which contained virtually no meat (a prime source of zinc), and consisted largely of unrefined wheat bread. While wheat and other cereal grains contain zinc, they also have a lot of phytates, fiber, and lignin, chemicals that bind to zinc in insoluble complexes that the intestines cannot absorb.
Much of the developing world eats a similar sort of diet, leading to widespread zinc deficiency, says Public Health's chair of International Health Robert Black. Researchers now know that zinc is essential for more than 200 enzyme systems. In addition to slowing growth and development, zinc deficiency can impair reproduction, immunity, the senses of taste and vision, and cognition.
What's New at Hopkins:
Public health researchers around the world are discovering that zinc supplementation can prevent or curb numerous illnesses that are common in developing countries. A conference on zinc deficiency and child health and development organized last year by the School of Public Health highlighted many promising findings. For example, in his studies in India, Black found that zinc supplements reduce rates of pneumonia and diarrhea in young children. Diarrhea is a significant cause of retarded growth and death in the developing world.
In Papua New Guinea, where 40 percent of the children under five are infected with malaria parasites, researchers led by Hopkins immunologist Anuraj Shankar found that zinc and vitamin A supplements significantly reduced malaria attacks in young children. "We think zinc supplementation is increasing immunity, which is involved in controlling malaria parasites," says Shankar, who is now testing this hypothesis in the lab. Shankar is also studying whether giving pregnant women zinc supplements increases their chances of having babies with higher levels of resistance.
What We Can Do:
Further studies are needed to assess the prevalence of zinc deficiency and find the most effective way to prevent related health problems. A year's supply of zinc supplements costs $1 per child. But researchers also plan to examine strategies for fortifying foods with zinc.
Rich sources of zinc include red meat, oysters, turkey, liver, and wheat germ. A caveat: doses of zinc higher than the recommended amount can reduce copper absorption and hinder immune function. --MH
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