Persistent Organic Pollutants among Overweight and Obese Pregnant Women and the Relationship with Glycemic Functioning
Open AccessIntroductionExposures to persistent organic pollutants (POPs) during pregnancy are associated with adverse health effects. Animal and human studies suggest certain POPs may impact glucose metabolism; however, few epidemiologic studies have examined environmental determinants of glycemic outcomes during pregnancy. Low-income, minority women with pre-existing co-morbidities may be particularly vulnerable to these exposures, but have historically been understudied. This dissertation is separated into two aims, both of which are based on the same study population of overweight and obese pregnant women. The first aim of this dissertation was to characterize exposures to multiple chemical classes among a sample of ethnically diverse, lower income, overweight or obese pregnant women. The second aim was to evaluate associations between exposures to individual and mixture of POPs and measures of prenatal fasting glucose, insulin, and insulin resistance during pregnancy in overweight women. MethodsSerum concentrations of polybrominated diphenyl ethers (PBDEs) and their hydroxylated metabolites (OH-PBDEs), polychlorinated biphenyls (PCBs), and poly- and perfluoroalkyl substances (PFASs) were measured in 98 pregnant women (California; 2011-2013). Aggregate exposures were evaluated using correlational clustering, a “chemical burden” score, and principal components analysis (PCA). Associations between sociodemographic characteristics and individual and aggregate exposures were evaluated using multivariable linear regression. We then assessed the association between POPs and glycemic outcomes among a subset of pregnant women from our first analysis (N=95). Outcomes included serum concentrations of fasting plasma glucose, fasting plasma insulin, and calculated homeostatic model assessment of insulin resistance (HOMA-IR). Generalized linear models were used to evaluate cross-sectional associations between individual and aggregate POPs and mean percent difference in fasting glucose, fasting insulin, and HOMA-IR. Bayesian kernel machine regression (BKMR) was used to assess the relative importance of each exposure to the association with our outcomes, using conditional and group posterior inclusion probabilities (PIPs).Results In the first analysis, both clustering and PCA produced four groupings: (PC1) PBDEs/OH-PBDEs, (PC2) PCBs, (PC3) PFNA/PFOA/PFDeA, (PC4) PFHxS/PFOS. Race/ethnicity and pre-pregnancy BMI were associated with PBDEs, OH-PBDEs and PC1. Maternal age was associated with PCBs and PC2. Parity was associated with PBDEs, OH-PBDEs and PC2. Poverty was negatively associated with PCBs whereas food insecurity was positively associated with PFOS. We observed variations in sociodemographic profiles of exposures by chemical class and weak across-class correlations. In the second analysis, the direction of associations between PBDEs and OH-PBDEs and fasting glucose, fasting insulin and HOMA-IR were varied. A doubling of PCB-138, PCB-153, PCB-180, and ∑PCBs concentrations was associated with a 2.10% mmol/L (95%CI: 0.49%, 3.74%), 2.10% mmol/L (95%CI: -0.14%, 4.39%), 2.10% mmol/L (95%CI: 0.12%, 4.12%), and 2.81% mmol/L (95%CI: 0.38%, 5.31%) increase in fasting glucose, respectively. Exposure to individual PCBs was positively associated with both fasting insulin and HOMA-IR. All PFAS were inversely associated with fasting glucose, fasting insulin, and HOMA-IR. In BKMR models of fasting glucose, all four chemical classes were important contributors to the overall mixture, with PFASs identified as the most important contributor. DiscussionIn a diverse group of overweight and obese pregnant women, sociodemographic characteristics of both individual POP chemicals and chemical groupings were identified, adding to the growing body of literature on chemical stressors during pregnancy. These findings have implications for epidemiologic studies of chemical mixtures and for exposure reduction strategies. Subsequently, we found variability in the direction and magnitude of the association within and across four POPs chemical classes and biochemical indicators of dysglycemia during pregnancy. Further examination of the relationship between POPs exposure and glycemic functioning in women during pregnancy is warranted.
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