Leaden calcium supplements.

Most calcium sources naturally contain lead. That may explain why two studies of calcium supplements last year found many brands to be laced with lead. The findings fueled concern about the potential for subtle lead poisoning, especially in children or in women taking calcium to prevent osteoporosis.

Australian scientists now argue that risks of such poisoning may not be as grave as suspected. They find that the body absorbs less lead when the metal is taken with calcium.

As a geochemist, Brian L. Gulson of Macquarie University in Sydney knew that calcium competes with lead for binding to molecules in cells. So, he and his coworkers pilot tested how much of a supplement's lead people actually absorb. They gave roughly 1 gram of calcium daily to 15 men and women for 6 months. Seven received tablets of calcium carbonate; the rest got a supplement made of three other forms of calcium.

The lead in the calcium carbonate tablets, which were made from U.S. calcium sources, has a different ratio of isotopes from Australia's lead. During the new trial, lead isotope ratios in the blood of Australians getting the U.S. calcium changed from their native ratio to one indicative of U.S. lead. The other supplement, which also came from foreign calcium sources, didn't alter lead-isotope ratios.

Even though both supplements added 3 micrograms of lead daily to each volunteer's diet, neither supplement raised anyone's blood concentration of lead, the scientists report in the March ENVIRONMENTAL HEALTH PERSPECTIVES. Gulson concludes that "alarmist stories about lead in calcium supplements are really not valid."

Bruce P. Lanphear of Children's Hospital Medical Center in Cincinnati remains skeptical. He points out that the altered lead-isotope ratio in people taking the calcium carbonate tablets shows its lead "is absorbed" to some degree. That's worrisome, he says, because his team finds adverse effects of lead at even barely detectable concentrations.

Even if an adult's lead absorption is low in the presence of calcium, that doesn't necessarily mean a child's would be, adds lan Tebbett of the University of Florida in Gainesville. Since his own study of calcium supplements last year showed that many brands contain negligible amounts of lead, he now argues that the government should require all others to get the lead out.