Association between bisphenol A and abnormal free thyroxine level in men

Bisphenol A (BPA) is a chemical that is used in a variety of consumer products, and exposure to BPA is widespread among the general population. Recent studies have suggested that BPA may affect the thyroid and related pathways. However, human studies are still limited. The aim of this study was to determine the relationship between BPA exposure and thyroid function. We obtained survey data and blood samples from The Thai National Health Examination Survey IV 2009, a nationally representative cross-sectional survey using a multistage, stratified sampling of the Thai population. A total of 2,340 subjects aged 18–94 years were sampled for the present study. Serum BPA, TSH, FT₄, and related covariates were measured. BPA was log-transformed prior to analysis. BPA was detected in 52.8 % of serum samples with a median concentration of 0.33 (range 0–66.91) ng/mL. We excluded subjects who tested positive for thyroid autoantibody and then stratified the remaining subjects by gender; the analysis showed a significantly negative correlation between serum BPA and FT₄ levels in males (r = −0.14, P < 0.001). In contrast, no association was observed in females. BPA was not associated with TSH in either gender. This gender-related discrepancy is possibly related to androgen-related differences in the metabolism of BPA. Our preliminary results provide evidence of a negative association between BPA and FT₄ levels. Additional detailed studies are needed to investigate the temporal relationship and potential public health implications of such an association.