Jan. 21, 2010 -- A chemical compound used to make non-stick cookware, food wrappers, and water-resistant coatings for carpets and fabrics has been linked to an increased risk for thyroid disease in an early study.
Perfluorooctanoic acid (PFOA) has previously been shown to influence thyroid hormone levels in animals.
But the newly reported study is among the first to suggest that exposure to PFOA might cause thyroid disease in humans.
The study included nearly 4,000 adults who took part in the CDC’s ongoing nationwide Health and Nutrition Examination (NHANES) study between 1999 and 2006.
Researchers found that participants who had the highest levels of PFOA in their blood also had the highest self-reported incidence of thyroid disease.
Specifically, women with the top 25% of PFOA concentrations were more than twice as likely to report taking drugs for thyroid disease as the 50% of participants with the lowest concentrations. A similar trend was seen in men, although it didn’t reach statistical significance.
The study does not prove that PFOA exposure is a direct cause of thyroid disease, researcher David Melzer, PhD, of Peninsula Medical School in Exeter, England, tells WebMD.
“I personally am far from sure, but it might prove to be an important risk factor for people who are already susceptible,” he says.
DuPont: PFOA Emissions Reduced
PFOA, also known as C8, and the related chemical perfluorooctane sulphonate (PFOS) are used by companies like DuPont and 3M in the manufacture of a range of products, including Teflon, Stainmaster, and Scotchgard.
Concerns have been raised about the man-made chemicals because they are now found in low levels in the environment and in the blood of most people and they remain in the blood for many years.
It is not clear how PFOA gets into the blood. Manufacturers claim their products do not contain it or contain only trace amounts of the chemicals.
The Environmental Protection Agency (EPA) is investigating the compound, but at present it considers the routine use of consumer products made with it to be safe.
In 2006, the EPA and eight major companies, including DuPont and 3M, agreed to work to eliminate global emissions of PFOA and related compounds by 2015.
A spokeswoman for DuPont tells WebMD the company has reduced PFOA emissions at its manufacturing sites worldwide by about 98% since that time, exceeding the interim target of 95% emission reduction by this year.
In response to the latest study, Janet Smith of DuPont points to research in communities with high PFOA exposures that show little or no impact on the thyroid.
“As the authors of the study indicated, it is not clear whether the associations they observed are causal,” she says. “Epidemiological studies involving workers who have had much higher levels of PFOA exposure than the general public haven’t shown any changes that would indicate impact on the thyroid.”
Thyroid Disease Link
Thyroid disease is much more common in women than in men. But the researchers found no evidence of a statistically different effect of PFOA exposure in women and men.
They did find a link between thyroid disease and higher concentrations of PFOS in men, but not in women.
Previous studies examining people living in communities where PFOA and PFOS are manufactured have shown little association between exposure to the chemical and thyroid hormone functioning.
But findings from the largest-ever study of PFOA exposure have not yet been made public.
In the ongoing C8 Study, researchers measured PFOA levels and health outcomes among nearly 70,000 residents of West Virginia who drank water contaminated with PFOA.
The study is funded by a $107 million lawsuit settlement agreed to by DuPont in 1998.
Preliminary findings suggest high PFOA levels may be linked to high blood pressure, high cholesterol, and impaired liver function.
University of Massachusetts thyroid researcher Thomas Zoeller, PhD, tells WebMD that thyroid disease is increasing, but the reasons for this remain unknown.
“There is almost certainly an environmental component to this, but we don’t know what that environmental component is,” he says.
He says PFOA and PFOS may be environmental triggers, but this remains to be proven.
And because it is not clear how people become exposed, there is no easy message for reducing exposure to these chemical compounds, he says.
“Right now, I don’t think we have the ability to know what kind of exposures we are getting and where it is coming from,” he says.