WEDNESDAY, Jan. 13 (HealthDay News) -- New research raises the possibility that people who have the highest levels of a chemical known as BPA in their urine are more likely to be diagnosed with heart disease.
But the findings don't prove that bisphenol A (BPA) actually causes heart disease -- one scientist even suggests other factors may be at play -- and researchers can't explain why statistics suggest that urinary levels of the chemical dropped by one-third over just two years during the last decade.
Still, the numbers raise more questions about BPA, which is found in a huge variety of plastic products. "The risks associated with exposure to BPA may be small, but they are relevant to very large numbers of people," said study author Tamara S. Galloway, a researcher at the University of Exeter in England.
BPA, which is used to make hard, clear plastic and epoxy resin, is found in everyday items, from food and drink containers to electronic and medical equipment.
It has been linked to sexual dysfunction, heart disease, cancer, diabetes and even hyperactivity in girls. But the chemical industry questions the validity of studies and contends that BPA is safe.
"Studies of this type are very limited in what they tell us about potential impacts on human health. While they can provide helpful information on where to focus future research, by themselves they cannot and should not be used to demonstrate that a particular chemical can cause a particular effect. The public should be confident that BPA is one of the most studied chemicals. Regulatory bodies from around the world have recently completed scientific evaluations and found BPA safe in food-contact products, including canned foods and beverages," stated Steven G. Hentges, of the American Chemistry Council's Polycarbonate/BPA Global Group.
"The study itself does not establish a cause-and-effect relationship between BPA exposure and heart disease. In addition, the robustness of these limited findings is questionable, as fewer than 50 participants self-reported health conditions without medical confirmation," Hentges added.
Galloway and colleagues sought to confirm the results of their previous research that showed a link between BPA exposure and heart disease. They compared data regarding BPA levels in urine from 2003-2004 (in 1,455 people) to 2005-2006 (in 1,493 people), and reported their findings in the Jan. 13 edition of the online journal PLoS ONE.
The researchers don't know why the levels dropped by one-third over just two years, although they speculate that decreased use of BPA may explain it.
After adjusting their figures to reduce the chance that they'll be thrown off by factors such as the age, gender and race of the subjects, the researchers found that high urinary levels of BPA boosted the risk of heart disease by 1.3 to 1.4 times compared to those with low levels.
That doesn't necessarily mean BPA makes people have heart problems. Galloway acknowledged that heart disease could somehow affect the way that the body deals with BPA and might boost its levels.
"All we can say is that the two are associated, and that the association has now been shown in two independent study populations, making it unlikely to be a chance finding," Galloway said.
Another possible factor is the diet of those who had high BPA levels, said Dr. Hugh S. Taylor, director of Yale University School of Medicine's division of reproductive endocrinology and infertility.
"People who eat out of cans and plastic have higher BPA levels, however they also have a lot of other reasons to have heart disease. Bad diets are clearly a cause of heart disease as well," he said. "This study is interesting and should make people concerned; it does not prove that BPA causes heart disease."
To find out if one thing causes another, scientists often turn to the "gold standard" in medical research: a randomized, controlled double-blind study. In this case, people would be randomly assigned to either be exposed to BPA or not, then researchers would watch to see that happened.
However, in regards to potentially harmful BPA exposure, "this would be unacceptable to any ethics committee," Galloway said. "Also, based on the current data, it would likely be very hard to find enough people for the control group who did not have detectable levels of BPA in their urine."
In other words, almost everyone has BPA in their system, making it harder to figure out exactly what it does, if anything, to the body.
There's more on bisphenol A research at the U.S. National Institute of Environmental Health Sciences.
SOURCES: Tamara Galloway, Ph.D., professor, ecotoxicology, University of Exeter, U.K.; Hugh S. Taylor, M.D., director, division of reproductive endocrinology and infertility, Yale University School of Medicine, New Haven, Conn.; Steven G. Hentges, Polycarbonate/BPA Global Group, American Chemistry Council; Jan. 13, 2010, PLoS ONE, online