Phenols and parabens in relation to reproductive and thyroid hormones in pregnant women

Abstract

Introduction: Phenols and parabens are ubiquitous environmental contaminants. Evidence from animal studies and limited human data suggest they may be endocrine disruptors. In the current study, we examined associations of phenols and parabens with reproductive and thyroid hormones in 106 pregnant women recruited for the prospective cohort, "Puerto Rico Testsite for Exploring Contamination Threats (PROTECT)".

Methods: Urinary exposure biomarkers (bisphenol A, triclosan, benzophenone-3, 2,4-dichlorophenol, 2,5-dichlorophenol, butyl, methyl and propyl paraben) and serum hormone levels (estradiol, progesterone, sex hormone-binding globulin (SHBG), free triiodothyronine (FT3), free thyroxine (FT4) and thyroid stimulating hormone) were measured at up to two time points during pregnancy (16-20 weeks and 24-28 weeks). We used linear mixed models to assess relationships between exposure biomarkers and hormone levels across pregnancy, controlling for urinary specific gravity, maternal age, BMI and education. In sensitivity analyses, we evaluated cross-sectional relationships between exposure and hormone levels stratified by study visit using linear regression.

Results: An IQR increase in methyl paraben was associated with a 7.70% increase (95% CI 1.50, 13.90) in SHBG. Furthermore, an IQR increase in butyl paraben as associated with an 8.46% decrease (95% CI 16.92, 0.00) in estradiol, as well as a 9.34% decrease (95% CI -18.31,-0.38) in estradiol/progesterone. Conversely, an IQR increase in butyl paraben was associated with a 5.64% increase (95% CI 1.26, 10.02) in FT4. Progesterone was consistently negatively associated with phenols, but none reached statistical significance. After stratification, methyl and propyl paraben were suggestively negatively associated with estradiol at the first time point (16-20 weeks), and suggestively positively associated with estradiol at the second time point (24-28 weeks).

Conclusions: Within this ongoing birth cohort, certain phenols and parabens were associated with altered reproductive and thyroid hormone levels during pregnancy. These changes may contribute to adverse health effects in mothers or their offspring, but additional research is required.

Keywords: Parabens; Phenols; Pregnancy; Reproductive hormones; Thyroid hormones.

Figure 1

Results of the stratified linear regressions comparing Visit 1 and Visit 3 associations for BPA, BP-3, 2,4-DCP and 2,5-DCP. Size of the box refers to the precision of the estimate, bars represent the 95% confidence interval of each estimate. Effect estimates are portrayed as percent change in hormone level in relation to the interquartile range increase in urinary exposure biomarker. Asterisk added if the interaction term between exposure*visit had a p value <0.05. (2-column fitting)

Figure 2

Results of the stratified linear regressions comparing Visit 1 and Visit 3 associations for TCS, MPB, BPB and PPB. Size of the box refers to the precision of the estimate, bars represent the 95% confidence interval of each estimate. Effect estimates are portrayed as percent change in hormone level in relation to the interquartile range increase in urinary exposure biomarker. Asterisk added if the interaction term between exposure*visit had a p value <0.05. (2-column fitting)