Long-term Exposure to Air Pollution and Incidence of Type 2 Diabetes in the Nurses' Health Study and Nurses' Health Study II.

BACKGROUND Research has detected associations between air pollution exposure and type 2 diabetes (T2DM), but findings from large cohort studies are needed to ascertain the most influential pollutants, susceptible subpopulations, and low-level exposure associations. Our aim was to prospectively evaluate the association between long-term exposure to fine particulate matter (PM2.5) and nitrogen dioxide (NO2) and T2DM incidence in the Nurses' Health Study (NHS) and Nurses' Health Study II (NHSII) cohorts of U.S. women. METHODS Monthly PM2.5 and NO2 exposures were predicted from spatiotemporal models and linked to participants' residential addresses. We used Cox proportional hazards models to assess the association between 24-month moving average PM2.5 and NO2 exposure and self-reported, clinician diagnosed T2DM from 1992-2019. We adjusted for time-varying lifestyle factors, reproductive hormonal factors, and individual and neighborhood socioeconomic status (SES). Results were meta-analyzed. We evaluated whether relationships persisted at levels below the current U.S. EPA National Ambient Air Quality Standards (NAAQS). Lastly, we examined multiplicative and additive interactions by body mass index (BMI), smoking status, physical activity, neighborhood SES, and region. RESULTS Over follow-up, there were 19,083 incident T2DM cases among the 208,733 women in NHS and NHSII. In fully-adjusted single pollutant models, the HR for an interquartile range (IQR=4.9 µg/m3) higher 24-month average PM2.5 exposure was 1.05 (95% CI: 1.02, 1.08) for incident T2DM. The HR for an IQR (7.3 ppb) higher NO2 exposure was 1.05 (95% CI: 1.01, 1.09). Both associations were robust to co-adjustment. Associations remained stable when restricting to PM2.5 levels below the NAAQS as compared to the full dataset. Stronger associations were observed in individuals who had a BMI ≥30, were physically active, and resided in the Northeast. CONCLUSIONS Our results showed a positive association between T2DM and long-term exposure to PM2.5 and NO2, persisting even at levels below the current EPA NAAQS. https://doi.org/10.1289/EHP15673.