A Harvard University study supports what many public health specialists have long assumed: Hard plastic drinking bottles containing bisphenol A are leaching notable amounts of the controversial chemical into people's bodies. Researchers from the Harvard School of Public Health found that people who drank for a week from the clear plastic polycarbonate bottles increased concentrations of bisphenol A, or BPA, in their urine by 69 percent. The study released Thursday is the first to definitively show that drinking from BPA bottles increases the levels of the chemical in urine, researchers said. It was published on the Web site of the journal Environmental Health Perspectives. BPA is used in hundreds of everyday products. It is used to make reusable, hard plastic bottles more durable and to help prevent corrosion in canned goods such as soup and infant formula. "If you heat those bottles, as is the case with baby bottles, we would expect the levels to be considerably higher," said Karin B. Michels, senior author of the report and associate professor at the School of Public Health and Harvard Medical School. "This would be of concern, since infants may be particularly susceptible to BPA's endocrine-disrupting potential," she said. Canada banned the use of BPA in baby bottles in 2008. Numerous animal studies in recent years suggest that low levels of BPA might cause developmental problems in fetuses and young children and other ill effects. The health effects on adults are not well understood, although a recent large human study linked BPA concentrations in people's urine to an increased prevalence of diabetes, heart disease and liver toxicity. The U.S. Food and Drug Administration has said that products containing BPA are safe and that exposure levels, including those for infants and children, are below those that would affect health. But the F.D.A.'s own scientific advisory board criticized agency officials for relying on industry-funded studies to declare the chemical safe. Michael L. Herndon, an F.D.A. spokesman, said in an e-mail Thursday that a newly appointed chief scientist, Jesse Goodman, would "provide new leadership and take a fresh look at this important issue from a scientific and policy position." Thursday, an official with the American Chemistry Council discounted any suggestion that the Harvard study underscored a health risk. In an e-mail, Steven G. Hentges said the study showed that exposure to bisphenol A from use of the bottles was "extremely low" and below the mean BPA amounts reported by the Centers for Disease Control and Prevention for the U.S. population, "indicating that even exclusive use of polycarbonate bottles does not lead to unusually high levels of bisphenol A in the urine." Led by Jenny Carwile, a doctoral student, 77 Harvard students in the study drank all cold beverages from stainless steel bottles for a week to wash BPA out of their bodies. Most BPA is flushed from people's bodies within a matter of hours. Then the students were given two bottles made with BPA to drink all cold beverages from for one week. Urine samples taken over that week showed the students' BPA levels had spiked to levels normally found in the general population. Because the students did nothing different other than drinking from the BPA bottles, the researchers determined their urine concentrations / had come largely from the bottles.