Year-to-year variation in phthalate metabolites in the Midlife Women's Health Study.

Background: Humans are widely exposed to phthalates, which are metabolized in the body and excreted in urine. Phthalate metabolites are excreted within hours of exposure, making urinary phthalate biomarker concentrations highly variable.

Objective: The goal of this study was to characterize the long-term variability in phthalate biomarker concentrations in women across the midlife transition and to identify factors that may be associated with increased variability in those phthalate biomarker concentrations by analyzing longitudinal urinary phthalate metabolite data from the Midlife Women's Health Study (2006-2015).

Methods: A total of 741 women were enrolled in the study for a period of up to 4 years, during which they each provided 2-4 urine samples per year over 4 consecutive weeks that were pooled for analysis (1876 total pools). Nine phthalate metabolites were assessed individually and as molar sums representative of common compounds (all phthalates: ƩPhthalates; DEHP: ƩDEHP), exposure sources (plastics: ƩPlastic; personal care products: ƩPCP), and modes of action (anti-androgenic: ƩAA). Phthalate metabolites were analyzed by quartile using generalized linear models. In addition, the impact of explanatory variables (race, annual family income, and type of work) on phthalate quartile was examined using ordinal logistic regression models.

Impact Statement: Phthalate biomarker concentrations are highly variable among midlife women over time, and annual sampling may not be sufficient to fully characterize long-term exposure.