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 <2.5 μm in aerodynamic diameter (PM_2.5 ) and nitrogen dioxide (NO₂ ) and T2DM incidence in the Nurses’ Health Study (NHS) and Nurses’ Health Study II (NHSII) cohorts of US women. METHODS: Monthly PM_2.5 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 PM_2.5 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 US 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 hazard ratio (HR) for an interquartile range (IQR) (IQR = 4.9 μg/m³ ) higher 24-month average PM_2.5 exposure was 1.05 [95% confidence interval (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 PM_2.5 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 PM_2.5 and NO₂, persisting even at levels below the current EPA NAAQS. https://doi.org/10.1289/EHP15673.