In the first study of the effects on humans of exposure to a chemical widely used in plastic baby bottles and food containers, researchers found that the compound increases the risk for heart disease, liver problems, and type 2 diabetes in adults.

The study, published in this week’s Journal of the American Medical Association, adds fuel to a heated debate about the safety of the chemical, Bisphenol A, which has been the subject of scientific scrutiny in recent years. The findings, which are consistent with earlier animal studies that fostered concern about the chemical’s safety, were released yesterday to coincide with a Food and Drug Administration hearing on BPA.

In an editorial from the medical journal, two longtime critics of BPA, John Peterson Myers and Frederick vom Saal, urged federal regulators to limit the use of the chemical. “The FDA cannot, with scientific credibility, conclude that BPA is safe. We still don’t know how risky it is, but you can’t with certainty conclude that it is safe,” Mr. Myers, who is the chief scientist of a nonprofit group, Environmental Health Sciences, said.

Federal regulators defended their assessment that BPA levels found in plastic baby bottles and food packaging is safe. “A margin of safety exists that is adequate to protect consumers, including infants and children,” a senior FDA scientist, Laura Tarantino, said at an FDA hearing.

An earlier report by another federal agency reflected a deep divide within the scientific community over the safety of BPA. A draft report issued earlier this month by the National Toxicology Program, a part of the National Institute of Environmental Health, found there was “some concern” that BPA poses a health risk to babies and children. Yesterday, Senator Grassley sent a letter to the FDA’s commissioner, Dr. Andrew von Eschenbach, expressing concern over how an FDA safety panel has selected studies to review as part of a risk assessment of BPA.

BPA is a ubiquitous ingredient in plastic products. About 7 billion pounds of BPA are manufactured each year, and more than 90% of Americans have traces of it in their urine, according to the Centers for Disease Control and Prevention. BPA is commonly found in plastic baby bottles, beverage containers, the lining of canned food containers, and other hard plastics imprinted with the recycling numeral 7. Exposure to BPA occurs when the chemical leaches into food over time, particularly when heated.

So far, the research has not been conclusive in assessing the risk of exposure to BPA.

Still, researchers said the JAMA findings advance what is known about the chemical’s health impact on humans. “It’s a very important study that moves the science substantially forward,” the chairman of the Department of Community and Preventive Medicine at Mount Sinai’s School of Medicine, Dr. Philip Landrigan, said. “This is one more risk for heart disease and diabetes, along with smoking, cholesterol, and all the other factors we know about.”

The study’s findings could also bolster a number of lawsuits filed in recent months against manufacturers of products containing BPA. Earlier this year, a group of California lawyers filed a class-action lawsuit against five leading baby bottle manufacturers on behalf of babies and infants who allegedly were exposed to BPA. In May, an Arkansas woman filed a federal lawsuit against a company that makes plastic baby bottles, Playtex Products.

While the company declined to comment on pending litigation, it announced yesterday plans to launch a BPA-free bottle next month. Other major retailers and vendors — including Wal-Mart, Toys “R” Us, and Nalgene, — also have announced plans to phase out products with BPA.

A trade group representing the plastics industry, the American Chemistry Council, has defended the safety of products with BPA, saying exposure is too low to cause harm. In a statement yesterday, the group called the JAMA study’s conclusion “premature.” The chemical “is not a significant health concern at the trace levels present in some consumer products,” the executive director of the council’s Polycarbonate/BPA Global Group, Steven Hentges, said.

Others critical of the JAMA study faulted researchers who demonstrated an association between BPA and certain illness but fell short of proving the chemical caused disease.

“I’m not saying associations don’t matter, but essentially you’ve got to come to a study that shows there is some causation,” the associate director of the American Council on Science and Health, Jeff Stier, said. “I can find an association that people who use pencils have higher rates of cancer. If you start looking at everything you’ll start finding associations. It is the nature of statistics.”

Mr. Stier applauded the FDA for “standing up for sound science,” and said efforts to remove BPA from products would result in more expensive items. “Clearly this is the cause of the year,” he said, describing “activist groups” that have fostered fear among parents.

The co-author of “Baby 411” and a pediatrician in Texas, Dr. Ari Brown, said parents constantly ask her whether plastic bottles are safe. “I tell them that unfortunately, with environmental health concerns, the jury is still out and we may not know for 20 years or 50 years if some of these things do have a health impact on humans,” she said.

But Ms. Brown said she counsels parents to err on the side of caution. “If there is a safe, cheap alternative easily available, why not?” she said.