Background

Bisphenol A (BPA) is one of the most common chemicals in daily life and is present in polycarbonate plastics, epoxy resins, medical equipment, and plastic consumer products. Recent studies reported that BPA may affect thyroid hormones. Therefore, this study, which was stratified based on BMI, aimed to investigate the association between the urinary BPA concentration and thyroid function using levels of T3, T4, and TSH.

Methods

This study examined data of 6,478 adults aged 19 years and older from the Second Korean National Environmental Health Survey (KoNEHS 2012–2014). We measured BPA in urine and data on total triiodothyronine (T3), thyroxine (T4), and thyroid stimulating hormone (TSH) in serum from the 2nd KoNEHS study. Multiple regression analysis was performed to assess the association of urinary BPA concentrations with thyroid hormone after BMI stratification.

Results

Urinary BPA was negatively associated with thyroid hormone, particularly T3 (-0.627) in all subjects and T4 (-0.060, -0.098) both in all subjects and in the group with BMI ≥25.0 kg/m2. When stratified by BPA, T3 and T4 were significantly decreased with higher BPA exposure compared to levels with lower BPA exposure in subjects with BMI >25.0 kg/m2 (adjusted β = -3.402, 95% CI: -4.942, -1.862 vs. adjusted β= -0.209, 95% CI: -0.328, -0.090). However, no obvious associations were found between BPA concentration and TSH.

Conclusions

The results showing increased urinary BPA associated with decreased T3 and T4 levels in the higher BMI group is a new finding in Korean studies. However, to clarify the effects of BPA exposure on thyroid function, future studies are needed.