CHICAGO (AP) - Many over-the-counter calcium supplements that millions take to keep bones strong contain small amounts of lead that could be a health risk if recommended doses are exceeded, new research suggests.

Though manufacturers have reduced the lead content since the debate first surfaced several years ago, the authors say they re-examined the issue because doctors are increasingly recommending calcium supplements to menopausal women and other patients to prevent osteoporosis.

About 5 percent of the U.S. population takes the supplements, including a sizable number of menopausal women, who face an increased risk of osteoporosis as their bodies stop producing estrogen. About 10 million Americans suffer from the bone-thinning disease.

Calcium is often mined from ancient seabeds that also may contain lead, which in high doses can damage the nerves, blood cells and digestive system, causing such problems as irritability, fatigue, vomiting, convulsions and permanent brain damage.

However, the authors say their findings suggest supplements are generally safe and beneficial unless taken in larger-than-recommended doses for many years.

The authors tested 23 products in March; their results appear in Wednesday's Journal of the American Medical Association.

The authors found no detectable level of lead in 15 of the supplements. The remainder had from 1.74 micrograms to 3.43 micrograms per 1,500 milligrams of calcium. The dose generally recommended to help prevent osteoporosis is about 1,200 milligrams to 1,500 milligrams daily.

Experts have suggested that the body's total daily exposure to lead should not exceed 6 micrograms, said Dr. Edward Ross, a University of Florida nephrologist who conducted the study with toxicology experts at the school's Gainesville campus.

An editorial in the same issue, by a medical consultant for many calcium suppliers, says the industry has made great strides in getting lead out of supplements and criticizes the authors for sounding an unnecessary alarm.

"A backlash against calcium supplements - evoked by a lead scare - would unquestionably do far more harm ... than would continued ingestion of current supplements," Dr. Robert Heaney of Creighton University said in the editorial.

Heaney also is a spokesman for the National Osteoporosis Foundation, an advocacy group that seeks to reduce the prevalence of osteoporosis. The foundation promotes the use of calcium supplements when food intake of the mineral is inadequate.

Though the issue prompted a widely publicized 1997 California lawsuit that forced one manufacturer to reduce the lead in its products, many consumers remain unaware of the potential exposure.

"I'm just taking this because I'm old and I was told to for my bones and osteoporosis," said Eilene Boothby, 53, of Nevada City, Calif. "Now I have to go home and look on the back of my bottle."

Makers of the dietary supplements are not required to list lead content, and Ross said some advertise their products as being lead-free even when they contain small amounts of lead.

Ross said the findings should prod manufacturers into either further reducing lead content or listing the amount on the label.

A spokeswoman for Leiner Health Products Group, the manufacturer involved in the California case, said she hadn't seen the study and would not comment.

The lead amounts that Ross detected are substantially lower than those that prompted the California case, said Dr. Gina Solomon, a senior scientist with the Natural Resources Defense Council, an environmental advocacy group that filed the California lawsuit.

Copyright 2000 The Associated Press. All rights reserved.