Urinary haloacetic acid concentrations and thyroid function among women: Results from the TREE study

Background Disinfection byproducts (DBPs) have been shown to impair thyroid function in experimental models. However, epidemiological evidence is scarce. Methods This study included 1190 women undergoing assisted reproductive technology (ART) treatment from the Tongji Reproductive and Environmental (TREE) cohort from December 2018 to August 2021. Serum thyrotropin (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) were measured as indicators of thyroid function. FT4/FT3 and TSH/FT4 ratios were calculated as markers of thyroid hormone homeostasis. Dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), the two most abundant HAAs, in urine were detected to assess individual DBP exposures. Results After adjusting for relevant covariates, positive associations were observed between urinary TCAA concentrations and serum TSH and TSH/FT4 levels (e.g., percent change = 5.82 %, 95 % CI: 0.70 %, 11.21 % for TSH), whereas inverse associations were found for serum FT3 and FT4 (e.g., percent change = −1.29 %, 95 % CI: −2.49 %, −0.07 % for FT3). There also was a negative association between urinary DCAA concentration and serum FT4/FT3 (percent change = −2.49 %, 95 % CI: −4.71 %, −0.23 %). These associations were further confirmed in the restricted cubic spline and generalized additive models with linear or U-shaped dose-response relationships. Conclusion Urinary HAAs were associated with altered thyroid hormone homeostasis among women undergoing ART treatment.