Effects of Sociodemographic Characteristics, Comorbidity, and Coexposures on the Association between Air Pollution and Type 2 Diabetes: A Nationwide Cohort Study

BACKGROUND: Exposure to air pollution has been associated with a higher risk of type 2 diabetes (T2D), but studies investigating whether deprived groups are more susceptible to the harmful effects of air pollution are inconsistent. OBJECTIVES: We aimed to investigate whether the association between air pollution and T2D differed according to sociodemographic characteristics, comorbidity, and coexposures. METHODS: We estimated residential exposure to [Formula: see text] , ultrafine particles (UFP), elemental carbon, and [Formula: see text] for all persons living in Denmark in the period 2005–2017. In total, [Formula: see text] persons 50–80 y of age were included for main analyses of whom 113,985 developed T2D during follow-up. We conducted additional analyses on [Formula: see text] persons age 35–50 y. Using Cox proportional hazards model (relative risk) and Aalens additive hazard model (absolute risk), we calculated associations between 5-y time-weighted running means of air pollution and T2D in strata of sociodemographic variables, comorbidity, population density, road traffic noise, and green space proximity. RESULTS: Air pollution was associated with T2D, especially among people age 50–80 y, with hazard ratios of 1.17 [95% confidence interval (CI): 1.13, 1.21] per [Formula: see text] [Formula: see text] and 1.16 (95% CI: 1.13, 1.19) per [Formula: see text]. In the age 50–80 y population, we found higher associations between air pollution and T2D among men in comparison with women, people with lower education vs. individuals with high education, people with medium income vs. those with low or high income, people cohabiting vs. those living alone, and people with comorbidities vs. those without comorbidities. We observed no marked changes according to occupation, population density, road noise, or surrounding greenness. In the age 35–50 y population, similar tendencies were observed, except in relation to sex and occupation, where we observed associations with air pollution only among women and blue-collar workers. DISCUSSION: We found stronger associations between air pollution and T2D among people with existing comorbidities and weaker associations among people with high socioeconomic status in comparison with those with lower socioeconomic status. https://doi.org/10.1289/EHP11347