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Women exposed to perfluorinated chemicals (PFCs) are at increased risk of developing hypothyroidism, according to results from a large, population-based survey.

The study was published online July 17 in the Journal of Clinical Endocrinology & Metabolism.

 

"[PFCs] have been widely used in a variety of products worldwide for years," write Chien-Yu Lin, MD, PhD, from the Department of Internal Medicine, En Chu Kong Hospital, New Taipei City, Taiwan, and coauthors. PFC concentrations are widespread among people and wildlife, and as PFCs break down slowly, they can remain in tissue for years.

Although concerns have been raised regarding the effects of PFC exposure on thyroid function, the potential relationship has never been fully addressed in a nationally representative survey.

Therefore, Dr. Lin and colleagues studied a cohort of individuals aged 20 years and older who took part in the National Health and Nutrition Examination Survey (NHANES) during 2007-2010. NHANES is a population-based survey that gathers data on the health and nutrition of US households.

A total of 16,723 individuals were randomly assigned to receive examinations. Of those, the researchers were able to obtain data on PFC exposure as well as thyroid function from 1181 of the participants.

Even after adjusting for potential confounding variables such as age, sex, race, alcohol consumption, smoking, and urinary iodine, the researchers found that women with elevated serum levels of one type of PFC, perfluorooctanoate (PFOA), were more likely to have higher levels of triiodothyronine (T3).

The researchers also observed increases in levels of T3 and thyroxine (T4) in women who had elevated concentrations of another PFC, perfluorohexane sulfonate (PFHxS), in their serum. In addition, those levels increased inappropriately; that is, without the pituitary gland having signaled the thyroid to generate more hormones, the researchers say.

In contrast, men whose blood contained elevated levels of PFHxS tended to have lower levels of T4 compared with other individuals in the cohort.

Of note, according to the investigators, is that even though individuals who had histories of thyroid disease were excluded from the study, an association was seen between subclinical hypothyroidism and elevated levels of PFOA, PFHxS, and perfluorooctane sulfonate in women.

"To our knowledge, this is the first report to link serum PFC levels and thyroid measures in a nationally representative survey of U.S. adults," the authors write.

They add that even though some PFCs are no longer manufactured, more studies are needed to assess their long-term effects because the compounds can linger in tissue for years.

The authors have disclosed no relevant financial relationships.

J Clin Endocrinol Metabol. Published online July 17, 2013.

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