Jan. 12, 2010 - Nearly everyone in the U.S. carries the plastics chemical BPA in their bodies. But those with the highest BPA levels have the highest risk of heart disease, new data confirm.
BPA -- bisphenol A -- is one of the world's most heavily produced chemicals. More than 2.2 metric tons of BPA are used each year to make PVC pipes, epoxy resins that line food cans, food packaging, and drink containers. It can be detected in the bodies of more than 90% of Americans.
Animal studies suggest BPA can have a wide range of health effects. But it's not at all clear whether these animal studies are relevant to humans. In response to calls for data, the CDC in 2003-2004 began testing a representative sample of Americans for BPA as part of the huge NHANES data-collection study.
In 2008, University of Exeter researcher David Melzer, MB, PhD, led a U.K. research team that analyzed the CDC's 2003-2004 data. They found that high BPA levels were linked to a higher risk of heart disease, diabetes, and elevated liver enzymes.
Critics pointed out that the NHANES study looked at so many things, something was bound to seem risky just by chance. Was the BPA finding such a statistical blip?
No, Melzer says. His team analyzed a new set of CDC data collected in 2005-2006. Surprisingly, average BPA levels were 30% lower in the new study. Yet people with the highest BPA levels still had a significantly higher risk of heart disease.
"It is very clear that the connection is still there," Melzer tells WebMD. "It underlines the question mark we found between BPA and human health."
To estimate the size of the risk they found, Melzer calculates that a 60-year-old man in the top third of BPA levels (over 3.5 nanograms/milliliter urinary concentration) has a 10.2% chance of having heart disease. A 60-year-old man in the lowest third of BPA levels (under 1.4 ng/mL urinary concentration) has a 7% chance of having heart disease.
"As urinary concentrations of BPA are an approximate marker of longer-term BPA exposure, we expect these figures underestimate the true effect size. We can’t say by how much, as no long-term exposure data are available," Melzer says.
It's not clear why BPA levels were lower in 2005-2006 than in 2003-2004. Melzer notes that public awareness of possible BPA health effects may have contributed to the decline, though nobody really knows.
But at these lower overall BPA levels, there was a trend but no significant association between BPA and diabetes or liver enzymes. However, when data from both years was pooled, these links were highly significant.
While the Melzer study shows a link between BPA and heart disease, it in no way proves that BPA causes heart disease. Such proof may be hard to come by, as definitive studies would mean giving people BPA to see what happens. But longitudinal studies that track people with high BPA levels over time might provide clearer answers.
BPA: Possible Health Effects
BPA acts like estrogen in the body, and early research into human effects focused on this activity. But recent reports have suggested that even low doses of the chemical may, over time, damage the liver, disrupt the function of insulin-making cells in the pancreas, disrupt thyroid hormones, and promote obesity.
"Much of this debate has been hindered up till now by a lack of epidemiological data of sufficient statistical power to detect low dose effects," Melzer collaborator Tamara S. Galloway, PhD, tells WebMD via email. "That's why there has been so much interest in our current research on human health effects."
Galloway says there's a need to learn more about what causes the health risks they identified -- particularly whether they are caused by BPA itself or by something else linked to BPA exposure.
"The risks associated with exposure to BPA may be small, but they are relevant to very large numbers of people," she says. "This information is important since it provides a great opportunity for intervention to reduce the risks."
The FDA is conducting a safety assessment of BPA. That assessment, scheduled for release late last year, is still pending.
The U.S. National Institute of Environmental Health Sciences says there is some concern about BPA safety for fetuses, infants, and children but negligible concern over the chemical's reproductive toxicity for adults.
The American Chemistry Council, a group representing the chemical industry, has in the past defended the safety of BPA. In a written statement provided to WebMD, Steven G. Hentges, PhD, of the ACC's Polycarbonate/BPA Global Group, says the Metzer study does not prove a link between BPA and heart disease.
"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," Hentges says in a news release. "The study itself does not establish a cause-and-effect relationship between BPA exposure and heart disease."
But Gina Solomon, MD, senior scientist at the environmental group National Resources Defense Council, says the study is a missing piece that helps to solve the BPA puzzle.
"Already we know that BPA is associated with diabetes and metabolic disturbances, so it is not surprising this carries out to heart disease," Solomon tells WebMD. "These results make sense and really increase our level of concern that BPA is a public health threat."
Solomon also sees a silver lining in the finding that BPA levels dropped by nearly a third from 2003-2004 to 2005-2006.
"This is showing that the voluntary actions taken by manufacturers to remove BPA from their products may be having an effect," she says. "But even the lower levels found in this study are still linked to health effects, so more action needs to occur to protect the public."
Reducing BPA Exposure
The National Institute of Environmental Health Sciences (NIEHS) says there is some concern about BPA safety for fetuses, infants, and children but negligible concern over the chemical's reproductive toxicity for adults.
There's no way to avoid BPA entirely: It's in food, water, and air. But the NIEHS offers this advice for people who want to reduce their exposure to BPA:
- Don’t microwave polycarbonate plastic food containers. Polycarbonate is strong and durable, but over time it may break down from overuse at high temperatures.
- Polycarbonate containers that contain BPA usually have a No. 7 on the bottom, although not all containers with a No. 7 contain BPA.
- Reduce your use of canned foods.
- When possible, opt for glass, porcelain, or stainless steel containers, particularly for hot food or liquids.
- Use baby bottles that are BPA-free.
The current Melzer study appears in the online journal PLoSOne.