Association Between Diethylhexyl Phthalate Exposure and Thyroid Function: A Meta-Analysis

Abstract

Background: Diethylhexyl phthalate (DEHP) is widely used in industrial products, particularly as plasticizers and softeners. Because it is used extensively, DEHP has been detected in humans worldwide. Although epidemiological studies suggest that DEHP can disrupt the function of the hypothalamic-pituitary-thyroid (HPT) axis, evidence on the association between DEHP exposure and thyroid function remains inconclusive. Therefore, a comprehensive meta-analysis was performed to investigate the association between DEHP exposure and the HPT axis in humans. Methods: A literature search of the MEDLINE, EMBASE, and Web of Science databases was conducted to search for studies in which the correlation coefficient values or regression coefficient values between three major DEHP metabolites (i.e., monoethylhexyl phthalate [MEHP], mono [2-ethyl-5-hydroxyhexyl] phthalate [MEHHP], and mono [2-ethyl-5-oxohexyl] phthalate) and thyrotropin, free thyroxine (T4), or total T4 were determined. The association between DEHPs and thyroid hormone levels were evaluated using Pearson's correlation coefficients. Results: Thirteen eligible articles were included. Urinary MEHP and MEHHP concentration was negatively correlated with total T4. Pooled correlation coefficients between MEHP/MEHHP and total T4 were -0.02 [confidence interval (CI) -0.05 to 0.00] and -0.03 [CI -0.05 to -0.01], respectively. Urinary mono (2-ethyl-5-oxohexyl) phthalate concentration was positively correlated with thyrotropin, and the pooled correlation coefficient was 0.02 [CI 0.00-0.04]. Conclusions: The findings of this meta-analysis suggest a significant association between the exposure of DEHP metabolites and the function of the HPT axis.