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Perfluorinated chemicals (PFCs), a class of chemicals used in products ranging from stain-resistant fabrics to fire extinguishers, may increase levels of thyroid hormones, particularly among women, researchers reported.
In an analysis of NHANES data, there was a significant positive relationship between perfluorooctanoate (PFOA) and total T3 and between perfluorohexane sulfonate (PFHxS) and total T3 and total T4 among women, Chien Yu Lin, MD, PhD, of En Chu Kong Hospital in New Taipei City in Taiwan, and colleagues reported online in the Journal of Clinical Endocrinology and Metabolism.
For men, they saw an inverse association between PFHxS and free T4.
"These findings suggest an effect of low-dose PFOA and PFHxS in humans, although the potential biological significance of this effect is small and subclinical in the general U.S. population," they wrote.
PFCs are widely used in consumer and industrial goods, including fabrics, carpets, surfactants, lubricants, paper coatings, cosmetics, and fire-fighting foams. They are characterized by highly stable carbon-fluoride bonds.
In addition to PFOA and PFHxS, other PFCs include perfluorooctane sulfonate (PFOS) and perfluorononanoic acid (PFNA). The researchers noted that PFOA and PFOS are largely being phased out and replaced with short-chain PFCs such as PFHxS.
The researchers evaluated data from 1,181 patients age 20 and older included in the National Health and Nutrition Examination Survey (NHANES) in 2007-2008 and 2009-2010.
The mean serum concentrations of PFCs were as follows:
- PFOA: 4.15 ng/mL
- PFOS: 14.2 ng/mL
- PFNA: 1.54 ng/mL
- PFHxS: 2.00 ng/mL
In unweighted analyses, Lin and colleagues found a significant positive relationship between PFOA and both total T3 and free T3 in women, and free T3 in men. They also saw positive associations between PFOS and free T4 in women and negative associations between PFNA and total T3 in men.
Serum PFHxS correlated with total T4, free T4, total T3, and free T3 in women.
In results weighted for sampling strategy, the researchers found that significant positive relationships persisted between PFOA and total T3 and between PFHxS and total T4 and Total T3 in women.
Specifically, for women, a 1-unit increase in natural-log serum PFOA increased serum total T3 concentration by 6.628 ng/dL (P=0.035), and a 1-unit increase in natural-log PFHxS was associated with an increase of total T4 by 0.26 mcg/mL (P=0.002) and total T3 by 4.074 ng/dL (P<0.001), they reported.
The researchers also saw that an increase in natural-log PFHxS was tied to a decrease of natural-log free T4 by 0.016 ng/dL in men (P=0.019).
In dose-response analyses among women, mean serum levels of total T3 rose significantly with PFOA concentrations, with significant elevations in the third and fourth quartiles compared with the 1st (P=0.019 and P=0.048, respectively).
Serum total T3 and total T4 levels rose significantly with PFHxS concentrations, with significant increases in the fourth quartile compared with the 1st, they reported (P=0.016 and P=0.009, respectively).
Although further study is needed to clarify whether there's a causal relationship between PFC concentrations and thyroid function -- the study was limited by its observational nature and by its cross-sectional design -- the researchers said the findings "provide clues about where to focus future epidemiologic and toxicology research."
The researchers reported no conflicts of interest.
- Reviewed by F. Perry Wilson, MD, MSCE Instructor of Medicine, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner
Journal of Clinical Endocrinology & MetabolismSource Reference: Wen LL, et al "Association between serum perfluorinated chemicals and thyroid function in U.S. adults: the National Health and Nutrition Examination Survey 2007-2010" J Clin Endocrinol Metab 2013.