Mediation effects of thyroid function in the associations between phthalate exposure and glucose metabolism in adults

The mediating influence of thyroid function on the association of phthalate exposure with glucose metabolism, including insulin resistance, remains unclear. We explored the mediating influence of thyroid hormone levels on the phthalate exposureeinsulin resistance association. This cross-sectional study of 217 Taiwanese adults assessed insulin resistance (Homeostatic Model Assessment for Insulin Resistance, HOMA-IR scores) and the levels of 11 urinary phthalate metabolites and 5 thyroid hormones. Multiple regression models were used to analyze the associations among serum thyroid hormone levels, urinary phthalate metabolite levels, and HOMA-IR scores. The mediation analysis assessed the influence of thyroid function on the phthalate exposureeHOMA-IR association. Our data indicated urinary monoethylhexyl phthalate (MEHP) levels was negatively associated with free thyroxine (T4) (beta =-0.018; 95% confidence interval [CI]:-0.031,-0.005) and positively associated with HOMA-IR scores (beta = 0.051, 95% CI: 0.012, 0.090). The study also revealed urinary mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) levels was negatively associated with free T-4 (0 =-0.036, 95% CI:-0.056,-0.017) and HOMA-IR (beta = 0.070, 95% CI: 0.013, 0.126). Free T-4 and HOMA-IR had a negative association (beta =-0.757, 95% CI:-1.122,-0.392). In the mediation analysis, free T-4 mediated 24% and 35% of the associations of urinary MEHP and MEOHP with HOMA-IR, respectively. Our findings revealed the mediating role of thyroid function in the phthalate exposureeglucose metabolism association in adults. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the mediating influence of thyroid hormone levels on the association between phthalate exposure and insulin resistance. Results indicated that thyroid function plays a crucial mediating role in the relationship between phthalate exposure and glucose metabolism.