Elevated exposure to bisphenol A has been linked in a new study to a significantly increased risk of cardiovascular disease, the second time researchers have made a connection between the widely used plastic-making compound and heart ailments.
The finding, released Tuesday, is likely to add to the controversy over the risks to adults of bisphenol A, which has been designated as a toxic compound by Health Canada and removed from plastic baby bottles as a safety precaution, but is still used as a liner inside almost all food and beverage cans sold in Canada.
According to the new research, 60-year-old American males with the highest amounts of bisphenol A in their urine had about a 45 per cent greater risk of cardiovascular disease than men the same age with lower exposures, confirming the results of a previous study on the topic released in 2008 and based on a different sample of people.
That earlier study was the first large medical review to show human health effects from BPA, as the chemical is also known, and could have been a fluke. Up until now, most research linking the chemical to harm has been done on laboratory animals, where it has been associated with such conditions as breast cancer and earlier sexual maturity in females.
The second finding of a heart-disease connection "underlines the question mark over the human health safety of BPA; it means that [earlier]association wasn't just a one-off thing," says David Melzer, an epidemiologist at Peninsula Medical School in Britain and a member of the team that conducted both studies.
The research has renewed calls for Health Canada to cut adult exposure to bisphenol A by banning the compound from food and beverage cans, which are thought to be the main place people pick up residues of the chemical.
"The evidence is now overwhelming that human exposure to bisphenol A is at the root of significant human disease, and that one of the most important things we could do for public health is to reduce human exposure to this chemical," said Rick Smith, executive director of Environmental Defence, an advocacy group.
Health Canada said in an e-mailed statement that it hadn't had a chance to review the new study, but it "continues to monitor new scientific evidence … and will take further action to protect the health of Canadians, if necessary."
While Health Canada has previously expressed concerns that infants might be getting too much of the chemical, it has said adult exposures were not a health threat.
BPA is a man-made compound not found in nature, and able to mimic estrogen, which creates worries that exposure to it amounts to an extra dollop of the female hormone. BPA is one of the largest-volume manufactured chemicals in the world, used in such everyday products as polycarbonate plastic water jugs, the plastic-like liners on the insides of tin cans, and some types of carbonless cash-register receipts, among other items.
Traces of BPA leak from consumer products, and that's the reason biomonitoring surveys in the U.S. have found that more than 90 per cent of the population carries detectible levels of it. Although the amounts in canned foods and drinks are minuscule - typically only a few parts per billion - this is still about 1,000 times the natural concentration of estrogen in people over all.
While the new study found an association between higher-than-average BPA levels and heart disease, Dr. Melzer cautioned that the research, published in the open-access journal PLoS One, doesn't prove the chemical causes heart-related ailments.
Such definitive proof would require dosing humans in clinical trials to observe heart-disease rates, something that wouldn't be allowed for ethical reasons. While BPA may be an additional risk factor for heart problems, Dr. Melzer recommended that people continue to be mindful of more proven steps to reduce risks, such as quitting smoking and monitoring cholesterol.
In the study, researchers compared reports of cardiovascular disease among about 1,500 people who participated during 2005 and 2006 in the most recent BPA biomonitoring survey funded by the U.S. government. The United States is the only country to have conducted and released results of its two population-based surveys for BPA. The newest survey found average levels of the chemical at 3.3 parts per billion, a drop of about 30 per cent from the only previous monitoring, done in 2003 to 2004.
It is not known why BPA levels fell over the period, but Dr. Melzer speculated it might be due to worried manufacturers removing the chemical from some uses that contact food.
Research based on the first survey also linked BPA to adult-onset diabetes, an association that was weaker in the second batch of people, possibly due to the decline in bisphenol A levels.
Statistics Canada has taken BPA samples in about 5,000 people, the largest such biomonitoring effort in the world. It expects to report results this summer, which will allow researchers to check whether the association with heart disease is occurring in Canadians.
The American Chemistry Council, an industry trade group representing BPA manufacturers, criticized the study and defended the safety of the chemical, which has been approved for use by regulatory bodies. "The study itself does not establish a cause-and-effect relationship between BPA exposure and heart disease," commented Steven Hentges, a spokesman for the group.