Are Particulate Matter Exposures Associated with Risk of Type 2 Diabetes?

BACKGROUND: Although studies have found that diabetes mellitus (DM) modifies the impact of exposures from air pollution on cardiovascular outcomes, information is limited regarding DM as an air pollution-associated outcome. OBJECTIVES: Using two prospective cohorts, the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS), we investigated the relationship of incident type 2 DM with exposures to particulate matter (PM) < 2.5 mu m (PM2.5), PM < 10 mu m (PM10), and PM between 2.5 and 10 mu m in aerodynamic diameter (PM10-2.5) in the previous 12 months and the distance to roadways. METHODS: Cases were reported and confirmed through biennial and supplemental questionnaires of diagnosis and treatment information. During follow-up from 1989 to 2002, questionnaires provided information on time-varying covariates and updated addresses. Addresses were geocoded and used to assign air pollution exposures from spatiotemporal statistical models. RESULTS: Among participants living in metropolitan areas of the northeastern and midwestern United States, there were 3,784 incident cases of DM in the NHS, and 688 cases in the HPFS. Pooled results from random effects meta-analysis of cohort-specific models adjusted for body mass index and other known risk factors produced hazard ratios (HRs) for incident DM with inter-quartile range (IQR) increases in average PM during the 12 months before diagnosis of 1.03 [95% confidence interval (CI), 0.96-1.10] for PM2.5, 1.04 (95% CI, 0.99-1.09) for PM10, and 1.04 (95% CI, 0.99-1.09) for PM10-2.5. Among women, the fully adjusted HR for living < 50 m versus >= 200 m from a roadway was 1.14 (95% CI, 1.03-1.27). CONCLUSIONS: Overall, results did not provide strong evidence of an association between exposure to PM in the previous 12 months and incident DM; however, an association with distance to road (a proxy marker of exposure to traffic-related pollution) was shown among women.