The first large-scale human study of a chemical used to make plastic baby bottles, aluminum can linings and myriad other common products found double the risk of cardiovascular disease, diabetes and liver problems in people with the highest concentrations in their urine, British researchers reported Tuesday.
The findings confirm earlier results obtained in animals, increasing pressure on the U.S. Food and Drug Administration to limit use of the chemical bisphenol A, or BPA.
The compound is the primary ingredient of polycarbonate plastics, which are found in a wide variety of modern goods, including DVDs, reusable food storage containers, drinking bottles and eyeglass lenses.
There have been growing concerns about its safety as studies in rodents have linked it to diabetes, brain damage, developmental abnormalities, precancerous changes in the prostate and breast, and a variety of other health problems.
About 7 billion pounds of the chemical are produced worldwide each year, and studies by the federal Centers for Disease Control and Prevention have found that 93% of Americans have detectable levels in their urine.
The new findings were published in the Journal of the American Medical Assn., coinciding with an FDA hearing Tuesday in Washington on BPA.
"This is a human study that really calls into question FDA's assertion that BPA is safe," said Dr. Anila Jacob of the activist Environmental Working Group.
An FDA representative, however, defended the agency's actions at the hearing.
"A margin of safety exists that is adequate to protect consumers, including infants and children, at the current levels of exposure," said Laura Tarantino, a senior FDA scientist.
But many experts think the writing is on the wall for the chemical.
A draft report issued this year by the government's National Toxicology Program, which has no regulatory authority, concluded that there was "some concern" that the chemical posed a risk to fetuses, babies and children.
Health Canada, that country's national public health agency, also this year released a report calling BPA "a potentially harmful chemical" -- becoming the first regulatory body in the world to do so.
Baby bottle manufacturers are already looking for replacements for the chemical. And Wal-Mart Stores Inc. and Toys R Us Inc. have announced plans to shift away from products containing BPA.
BPA was first synthesized in 1891 and came into wide use in the 1940s and 1950s because of the durability and light weight of polycarbonates.
Some BPA remains intact in the plastic and leaches out over time, particularly when it comes in contact with hot liquids or acidic foods.
The chemical industry and the FDA have long relied on two large animal studies showing that high concentrations of the chemical fed to rodents produced no serious adverse effects.
There had been no previous large studies of the chemical in humans because researchers considered such testing inappropriate.
Dr. David Melzer of the Peninsula Medical School in Exeter, Britain, and his colleagues took advantage of results from the 2003-04 U.S. National Health and Nutrition Examination Survey, which for the first time measured concentrations of BPA in urine from a representative sample of 1,455 adults.
They found that the quarter of the group with the highest BPA levels -- levels still considered safe by the FDA -- were more than twice as likely to suffer from diabetes and cardiovascular disease as the quarter with the lowest levels.
The study, funded by the medical school, discovered no association with any other health effects.
But the findings were sufficiently troublesome that the FDA should take "aggressive action to limit human and environmental exposures," wrote biologists Frederick S. vom Saal of the University of Missouri and John Peterson Myers of Environmental Health Sciences in Charlottesville, Va., in an editorial accompanying the study.
Steven G. Hentges of the American Chemistry Council, whose members include polycarbonate makers, objected that the study's design, which measured BPA at only one point in time, "cannot support a conclusion that bisphenol A causes any disease."
The authors partially agreed, calling for follow-up studies to confirm their findings and prove whether the link is causal. But, Jacob noted, the similarities between the British results and those of animal studies suggest that it is.
The cause of the increased risk is unclear, but two studies this year offered some hints. Spanish researchers reported in April that in mice, BPA caused pancreatic cells to increase their production of insulin, leading to the well-known metabolic syndrome that is a precursor of diabetes and heart disease.
And an August study by endocrinologist Nira Ben-Jonathan of the University of Cincinnati showed that BPA, like estrogen, impaired the ability of human fat tissue to secrete adiponectin, which protects against heart attacks and diabetes.
Meanwhile, there are some steps consumers can take to avoid BPA. A Japanese study of college students suggested that the major dietary source of BPA was canned beverages. Glass and recyclable plastic soda and water bottles do not contain polycarbonates.
Glass baby bottles are safe, and at least one company makes plastic baby bottles containing no BPA.
Nonrecyclable plastic containers that are made with polycarbonates are marked with the number 7 on the bottom. BPA leaching can be reduced by not microwaving food in such containers.