Environmental pyrethroid exposure and thyroid hormones of pregnant women in Shandong, China.

Abstract

BACKGROUND\nPyrethroid insecticides have been extensively used in China and worldwide, while their effects on thyroid functions are rarely explored, especially in susceptible pregnant women.\n\n\nOBJECTIVE\nTo assess the association between 3-phenoxybenzoic acid (3PBA), a major urinary metabolite of pyrethroids, and thyroid hormone levels in pregnant women in China.\n\n\nMETHODS\nThree hundred and seventy-four pregnant women were recruited during the admission for delivery (third trimester of pregnancy) in a local hospital in Shandong, China during December 2011 to December 2013. Pyrethoids exposure was assessed by examining urinary metabolite of 3PBA levels. Thyroid hormones were detected by measuring serum concentrations of thyroid stimulating hormones (TSH), total triiodothyronine (TT3), free triiodothyronine (FT3), total thyroxine (TT4) and free thyroxine (FT4). Multiple linear regression models were used to investigate the associations between 3PBA concentrations and thyroid hormones levels.\n\n\nRESULTS\nThe detection frequency of 3PBA was 90.4%, with a median concentration of 1.14\u202fμg/g creatinine. After adjusted for potential confounders, we found a significant negative relationship between 3PBA and serum FT3 (β\u202f=\u202f-0.06, 95% CI\u202f=\u202f-0.11 to\xa0-0.01) as well as an inverse dose dependent association (p for trend\u202f=\u202f0.023). No significant association was found between 3PBA concentrations and other thyroid hormones.\n\n\nCONCLUSIONS\nOur findings indicated that pyrethroid exposure was widespread and negatively associated with serum FT3 concentrations in pregnant women in northern China. Given to the widespread of pyrethroid exposure and critical role thyroid homeostasis plays during pregnancy, more studies are warranted to explore their relationships as well as underlying mechanisms.