Meanwhile, the first large-scale study of BPA's effects on people linked the chemical to an increased risk of Type 2 diabetes and heart disease.
Together, the news touched off a new round of debate on BPA, which for the past several years has faced increasing criticism from some scientists and consumer advocates over possible neurological, reproductive and other health effects.
BPA, which is found in products including water bottles, baby bottles and the lining of metal cans, mimics the hormone estrogen in the body.
In the new study, published Tuesday in the Journal of the American Medical Association, researchers examined data from the 2003-04 National Health and Nutrition Examination Survey. The 1,455 participants in the government survey provided urine samples and answered questions about their health.
The researchers divided the group into four quartiles based on the amount of BPA in the participants' urine. They found that there were more than twice as many people with heart disease and Type II Diabetes in the quartile with the highest concentration of BPA than in the quartile with the lowest. All of the concentrations were below the level deemed safe by the government.
"The study by Lang et al should stimulate further studies and the reevaluation of the basic assumptions in chemical risk assessments that led to FDA assurances that BPA is safe," Frederick vom Saal, a researcher at the University of Missouri who discovered some of the first health effects of BPA in mice, wrote in an editorial published in JAMA.
But vom Saal acknowledged, as did the researchers themselves, that the study is only a first step -- it does not prove that BPA causes heart disease or diabetes in people.
"This is just an association, we can't say there's any causal mechanism," said researcher Iain Lang, of the Peninsula Medical School in the United Kingdom. "There's clearly more work that needs to be done to establish that."
That includes first replicating the findings in another group of people, Lang said, and then conducting long-term studies to see if people with higher levels of BPA are, over time, more likely to develop the diseases.
But previous work in animals and with human tissue suggests that there are ways that BPA could increase the risk of diabetes and heart disease.
In a study published last month, scientists at the University of Cincinnati exposed fat tissue taken from patients getting breast reduction and tummy tuck surgeries to both a form of estrogen called estradiol and to bisphenol A. They found that both compounds reduced the tissue's production of a hormone called adiponectin, which helps protect against both diabetes and cardiovascular disease.
Additionally, a decade of research has suggested that the BPA can cause numerous health problems in lab animals, including reproductive abnormalities and metabolic diseases like diabetes.
"It's these underlying mechanisms that make this paper stronger than it might be standing by itself," said Pete Myers, a scientist at the nonprofit group Environmental Health Sciences and a longtime critic of BPA.
Some researchers, however, said that there are inconsistencies in the paper's findings. Garret FitzGerald, a toxicologist at the University of Pennsylvania and one of the FDA's expert advisers on BPA, questioned why the research would show a link between BPA and cardiovascular disease, but not high blood pressure or lipid levels, which are precursors to heart disease.
"All of this does very tenuously raise a question [about BPA's link to heart disease]" FitzGerald said. "But we're just in the beginning stages of what seems to be a surprising and somewhat remote possibility."
The new findings were released ahead of an FDA hearing on the topic Tuesday. The FDA, which regulates the BPA's use in food containers, released a draft assessment in August that stated that levels of BPA in the environment are too low to cause health effects in humans.
But numerous scientists and advocates have since then criticized the FDA's assessment, which relied heavily on studies funded by industry.
The FDA asked an outside expert panel to review the scientific literature before the agency releases its final report, and during Tuesday's hearing scientists, consumer advocates and FDA officials spoke before the panel.
"A margin of safety exists that is adequate to protect consumers, including infants and children, at the current levels of exposure," FDA scientists Laura Tarantino told the panel, according to the Associated Press.
But the new study of human health effects was the talk of the afternoon, according to the Washington Post.
"This is the nail in the coffin," BPA opponent vom Saal told the paper. "This is a huge deal."