Medium- and Long-Term PM2.5 Exposures and Sudden Cardiac Death in a Prospective Cohort of US Women

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Background and Aim: Previous studies have reported associations between short-term exposure to fine particulate matter (PM2.5) and acute cardiac events. However, the effect of long-term exposure to PM2.5 on the risk of sudden cardiac death (SCD) is unknown. We prospectively examined associations between medium- and long-term exposures to PM2.5 and incidence of SCD in the Nurses’ Health Study (NHS) cohort, a nationwide prospective cohort of female nurses in the US. Methods: Women in NHS (N=117,358) were followed via biennial questionnaires. Spatiotemportal prediction models were used to estimate monthly time-varying, residential exposure to PM2.5. To enable examination of different time windows of exposure simultaneously, given the high correlation between time windows, we calculated cumulative average PM2.5, the difference between the cumulative average and 12-month moving average, the difference between the 12- and 3-month moving averages, and the difference between the 3- and 1-month moving averages. Confirmed SCD cases 1988-2013 were identified by medical records and next-of-kin reports. We used time-varying Cox proportional hazards models adjusted for preexisting conditions, demographics, socioeconomic status, region, and season to calculate hazard ratios (HR) and 95% confidence intervals (CI) for each exposure time window (in separate and co-adjusted models). We explored deviations from linearity with cubic splines. Results: During 2,070,412 person-years of the study, there were 320 confirmed SCDs. There was no evidence of deviations from linearity, therefore we present HRs from continuous models per 10µg/m3 increase in each of the time windows of PM2.5. In multivariable adjusted models, only the difference in exposures between the 12- and 3- month moving averages was associated with risk of SCD (HR=1.06; 95%CI: 1.00, 1.12). Conclusion: The results of the study suggest an association between medium-term PM2.5 exposure and SCD, suggesting that seasonal exposures may be an important time window of susceptibility. Keywords: Particulate matter, air pollution, sudden death