Urinary phthalate metabolites and phenolics in women of childbearing age and their association with thyroid hormones: a comparison study of fasting status

Abstract

[BACKGROUND AND AIM] Exposure to parabens and phthalates has been associated with thyroid hormones in humans. Epidemiologic observations, however, are often inconsistent depending on population, probably due to different susceptibility or other factors such as exposure misclassification. Fasting status may influence the urinary levels of many chemicals, especially when their major exposure pathways are related to diet. In the present study, we assessed the associations of urinary phthalate metabolites and phenolics with thyroid hormones in non-pregnant women of child-bearing age in Korea (20-49 years of age), considering fasting status. [METHODS] As a fasting population, we recruited women (n=254) who visited four hospitals after >9 hr of fasting between 2015 and 2016. From the fasting women, we measured phthalate metabolites and parabens in urine, and thyroid hormones in serum. Non-pregnant women of the same age group, who were not asked to fast, was chosen from KoNEHS Cycle 3 (2015-2017) (phthalate metabolites (n=341) and phenolics (n=340)). [RESULTS] Urinary concentrations of MEHHP, MEOHP, MBzP, and BPA were >2 folds higher in the non-fasting women, and those of MeP were higher in the fasting women. Regardless of fasting status, MeP and EtP levels showed significant negative association with both total and free T4. DEHP metabolites also showed negative associations with free T4 but positive associations with total T3. However, associations of MBzP and BPA with thyroid hormones varied by the fasting status, which might be due to the influence of diet on their urinary concentrations. [CONCLUSION] While certain chemicals like EtP and to lesser extent DEHP are known to be delivered through dietary factors, consistent associations with altered thyroid hormones regardless of fasting status are noteworthy. [KEYWORDS] thyroid hormones; fasting; phthalates; phenolics [Acknowledgement] This work was supported by grants from National Research Foundation of Korea (NRF) (NRF-2020R1A2C3011269 and NRF-2022R1C1C2006982).