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Common stain repellent linked to thyroid disease

Long-term health study shows connection with blood levels of perfluorooctanoic acid

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7:01pm, January 22, 2010
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Stain-repelling chemicals help keep carpets, upholstery and clothing clean — but the compounds may be messing up the body. Higher blood levels of the synthetic chemical perfluorooctanoic acid, or PFOA, are linked to thyroid diseases, scientists report online in Environmental Health Perspectives. It is the first report of such a connection between the widely used chemical and thyroid diseases in people and should prompt further studies, scientists say.

“We’re looking at a moment in time,” says study coauthor Tamara Galloway of the University of Exeter in England. The researchers analyzed data from the National Health and Nutrition Examination Survey, or NHANES, conducted by the U.S. Centers for Disease Control and Prevention in Atlanta. It provides a snapshot of the health of a representative sample of the U.S. population, but it can’t speak to cause and effect, she cautions. “These studies are very valuable if you are trying to look for subtle interactions,” which give clues that may warrant further investigation, says Galloway.

The researchers analyzed data from nearly 4,000 adults taken for NHANES from 1999 to 2006 and looked at blood levels of PFOA. The chemical is both a by-product and a building block of the coatings that make firefighter gear heat-resistant and that keep microwave popcorn bags from seeping grease and carpets from absorbing spills. The team looked for associations between blood levels of PFOA and each of several diseases, including diabetes, heart disease, asthma and liver disease, but only one stood out: thyroid disease. People with the higher PFOA levels were more than twice as likely to have thyroid diseases, which are characterized by an under- or overactive thyroid gland as well as metabolic and immune system problems.

The association was stronger in women, who are more prone to thyroid diseases than men. Of the sampled population, 163 women and 46 men reported that they were taking medication for thyroid problems.

PFOA is a type of perfluorochemical, or PFC, that has been manufactured directly and is a byproduct of producing other chemicals. Since the 1950s, PFCs have been used to make numerous products, including lubricants, paper and textile coatings, polishes, food packaging and fire-retardant foams.

These compounds of carbon chains decked out with fluorine atoms are extremely stable and persistent in the environment, people and wildlife, and NHANES data suggest that more than 98 percent of Americans have PFOA in their blood. Exposure routes aren’t clear, but probably include contaminated drinking water, dust and contact with products.

A number of animal studies suggest that PFOA may meddle with the balance of hormones in the body, although how exactly the chemicals act isn’t clear. “There’s very little mechanistic information — it’s a big black box,” comments toxicologist Abby Benninghoff of Utah State University in Logan. Nevertheless, the link to thyroid disease stands out, she says. “They looked at a lot of diseases,” she says. “This response seems specific for this disease.” 

Though more research is needed to assess the health effects of PFOA, a lack of certainty shouldn’t mean a lack of concern, says endocrinologist R. Thomas Zoeller of the University of Massachusetts Amherst. Studies required for airtight conclusions about long-term effects of these chemicals in humans would take decades and aren’t ethical to carry out. “We have to recognize those limitations,” Zoeller says. “We cannot continue to allow chemicals that bioaccumulate to be widely distributed.”

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