Does fetal zinc affect later immunity?

Does fetal zinc affect later immunity?

Even a mild zinc deficiency in a fetusmight lead to lasting, adverse effects on the immune system, according to new animal research. The study could have implications for humans, especially pregnant young teenagers who are socially disadvantaged and malnourished, says Pamela Fraker, who directed the study at Michigan State University in East Lansing. She worries that the demand for zinc by a pregnant 13- to 15-year-old's still-growing body could limit how much zinc the developing fetus gets.

Zinc is an essential trace metal. Becauseit is not stored in the body, it must be obtained daily from dietary sources --such as meat, seafood and vegetables. In Fraker's study, pregnant mice were fed a diet that was nutritionally balanced except for its zinc. Mice on the diet developed blood-zinc levels that were about 30 percent below normal. Fraker says this "marginal deficiency' produced no immediately observable symptoms other than a 10 to 15 percent smaller weight gain than in mice fed a fully balanced diet. At first glance, even litters of the marginally deficient animals appeared normal.

However, the Michigan State researchersfound, these mice produced pups whose blood-zinc levels at birth were only 60 percent of that in pups whose mothers had eaten a zinc-sufficient diet. And immune function in these "deficient' pups--as measured by the numbers of antibody-producing cells--"starts out at about 50 to 60 percent of normal and remains that way through puberty,' even when the pups are raised on a fully zinc-sufficient diet, Fraker says.

This finding contrasts with what happensin mice that become zinc deficient only after birth, in which case compromised immunity returns to normal as soon as the source of zinc deficiency is corrected. There are other signs, too, that in utero zinc deficiency may initiate unique immune-system changes. For example, Fraker notes, normally a zinc-deficient animal makes fewer lymphocytes and macrophages--cells important to immune function. However, her studies show, in animals deprived of zinc in utero, the normal numbers of lymphocytes and macrophages are present. "They just don't perform as well,' she says.

These data linking zinc and immunefunction are consistent with other studies of zinc deficiencies in animals, according to James C. Smith, chief of the Vitamin and Mineral Nutrition Laboratory at the Agriculture Department's Beltsville (Md.) Human Nutrition Research Center. However, Smith adds, to date there has been little research investigating whether a similar link exists in humans. "There are little tidbits' of data suggesting such a link, he told SCIENCE NEWS, "but nothing conclusive.'

Complicating the study of this link isthe fact that "we don't know how to measure zinc nutrition in humans,' explains William Beisel of the Johns Hopkins School of Public Health in Baltimore. Blood-zinc levels not only fluctuate rapidly, giving no measure of long-term zinc status, he says, but "even the slightest infection pulls zinc from the blood and dumps it in the liver.' In such cases, zinc is not lost to the body, just largely unavailable for measurement.