Exposure to Per- and Polyfluoroalkyl Substances and Mortality in US Adults: A Population-Based Cohort Study

BACKGROUND: Per- and polyfluoroalkyl substances (PFAS) are widespread environmental contaminants associated with diseases such as cancer and dyslipidemia. However, few studies have investigated the association between PFAS mixture exposure and mortality in general populations. OBJECTIVES: This study aimed to explore the association between PFAS mixture, perfluorooctanoic acid (PFOA), and perfluorooctane sulfonic acid (PFOS) and mortality in U.S. adults by a nationally representative cohort. METHODS: Adults >= 18 years of age who were enrolled in the National Health and Nutrition Examination Survey (NHANES) (1999-2014) were included in our study. Baseline serum concentrations of seven PFAS were measured and individuals were followed up to 31 December 2015. Hazard ratios (HRs) and confidence intervals (CIs) were estimated using Cox proportional hazards models. Association between PFAS mixture exposure and mortality was analyzed using the k-means method by clustering PFAS mixtures into subgroups. Association between PFOA/PFOS exposure and mortality was subsequently analyzed in both continuous and categorical models. RESULTS: During the follow-up period, 1,251 participants died. In the mixture analysis, the k-means algorithm clustered participants into low-, medium-, and high-exposure groups. Compared with the low-exposure group, participants in the high-exposure group showed significantly higher risks for all-cause mortality (HR=1.38; 95% CI: 1.07, 1.80), heart disease mortality (HR=1.58; 95% CI: 1.05, 2.51), and cancer mortality (HR=1.70; 95% CI: 1.08, 2.84). In single PFAS analysis, PFOS was found to be positively associated with all-cause mortality (third vs. first tertile HR=1.57; 95% CI: 1.22, 2.07), heart disease mortality (third vs. first tertile HR=1.65; 95% CI: 1.09, 2.57), and cancer mortality (third vs. first tertile HR=1.75; 95% CI: 1.10, 2.83), whereas PFOA exposure had no significant association with mortality. Assuming the observed association is causal, the number of deaths associated with PFOS exposure (>= 17.1 vs. <7.9 ng/mL) was similar to 382,000 (95% CI: 176,000, 588,000) annually between 1999 and 2015, and it decreased to 69,000 (95% CI: 28,000, 119,000) annually between 2015 and 2018. The association between PFOS and mortality was stronger among women and people without diabetes. DISCUSSION: We observed a positive association between PFAS mixture exposure and mortality among U.S. adults. Limitations of this study include the potential for unmeasured confounding, selection bias, a relatively small number of deaths, and only measuring PFAS at one point in time. Further studies with serial measures of PFAS concentrations and longer follow-ups are necessary to elucidate the association between PFAS and mortality from specific causes.