THURSDAY, Jan. 21 (HealthDay News) -- Chemicals found in carpeting, non-stick cookware and fabrics are linked to an increase in thyroid disease, new research suggests.
British researchers analyzed blood serum levels of two types of perfluorinated chemicals in nearly 4,000 U.S. adult men and women, using data from U.S. Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey (NHANES).
Women whose blood levels of perfluorooctanoic acid (PFOA) was in the highest quartile were more than twice as likely to report having thyroid disease as those in the lowest two quartiles. The findings were similar in men, but the results were not statistically significant.
Among men, researchers found an increase in the likelihood of thyroid disease among those who had high levels of perfluoroctane sulphonate (PFOS) in their blood, but the same association was not found in women.
The researchers cautioned that while the data show an association between the chemicals and thyroid disease, they do not prove cause and effect, meaning there could be other explanations for why people with high levels of the compounds in their blood had more thyroid disease.
"We have provided the first evidence of a statistical association between PFOA blood levels and thyroid disease in the 'ordinary' U.S. adult population," said senior study author Tamara Galloway, a professor of ecotoxicology at University of Exeter. "In this type of human population research, it is not possible to be sure whether this is cause or effect. That needs more research."
The study will be published Jan. 21 in the online issue of the journal Environmental Health Perspectives.
Thyroid disease is more common in women than men, and recent reports have found the incidence is rising. Among study participants, about 16 percent of women and 3 percent of men had a thyroid disorder at some point.
Perfluorinated chemicals are pervasive in industrial and consumer products, including food packaging, flame-resistant and waterproof clothing, chemical-resistant tubing and stain-resistant coatings for carpets. The chemicals are chosen for their ability to repel heat, water, grease and stains.
Previous research in animals has shown that the compounds may affect the thyroid, which helps maintain heart rate, regulate body temperature, metabolism, reproduction, digestion and mental health, according to background information in the study.
PFOA and PFOS have also been linked to cancer in animal studies, though research in humans have been inconclusive or have not found a link among the general population.
Because of concerns about toxicity, the U.S. Environmental Protection Agency got commitments from eight manufacturers of PFOA to reduce emissions and usage of PFOA and related chemicals by 95 percent this year, and to move toward eliminating usage of the chemicals completely by 2015.
But that doesn't mean the chemicals will soon be gone from the environment or people's bodies. PFOA and PFOS are also found in water, air and soil, even in remote areas of the globe. PFOA and PFOS have also been detected in the blood of birds, fish and polar bears.
"The formulations used in consumer goods tend to contain more complex forms of PFOA that are quite soluble and/or volatile and can be transported around the globe via ocean currents and in the atmosphere," Galloway said. "That's why PFOA and related compounds are found in every country so far studied."
In addition, the half-life of PFOA and PFOS in the human body is 3.8 years and 5.4 years, respectively, meaning that's how long it takes for half of the chemical to disappear.
The main source of human exposure to PFOA and PFOS is unknown, but it's believed to be through diet, such as from greaseproof food wrappings, researchers said. People may also inhale household dust that contained PFOA or PFOS from fireproof or waterproof coatings on fabrics or carpeting.
"The good news is that mean exposure concentrations seem to be falling over the last few years, coinciding with voluntary reductions in usage by the main manufacturers," Galloway said.
A large study of people living in Parkersburg, W.V., near a DuPont plant that produced perfluorinated chemicals, is ongoing. The residents have higher concentrations of PFOA in their blood than the general population.
Dr. Stephen Rosen, chief of endocrinology and metabolism at Pennsylvania Hospital in Philadelphia, said the study adds to a growing body of research that that suggests common household chemicals may have detrimental effects on human health.
Those chemicals include bisphenol A (BPA), which has been shown to be an endocrine disruptor with potential consequences for reproduction, and phthalates, which animals studies have also found to be endocrine disruptors.
As for PFOS and PFOA, "this is a nice preliminary study, but I wouldn't want to draw major conclusions from it," Rosen said. "However, it definitely should be studied further. These chemicals are ubiquitous in people's homes, and we need to determine if it could be a trigger for thyroid disease in people genetically predisposed."
The Hormone Foundation has more on thyroid disease.
SOURCES: Tamara Galloway, Ph.D., professor, ecotoxicology, University of Exeter, England; Stephen Rosen, M.D., chief, endocrinology and metabolism, Pennsylvania Hospital, and clinical associate professor, medicine, University of Pennsylvania Health System, Philadelphia; Jan. 21, 2010, Environmental Health Perspectives