Background/aim Recent studies suggested an association between long-term air pollution and type 2 diabetes (T2D). However, evidence is limited, especially for ultrafine particles (UFP, diameter <0.1 µm) having a high toxic potential due to their small size but comparably large surface. We investigated the association between residential air pollution and T2D prevalence determined at up to three time points.

Methods We conducted a longitudinal analysis based on data of the baseline survey (1999–2001), first (2006–2008) and second follow-up (2013–2014) of the KORA S4 cohort in the Augsburg region, Germany. Long-term exposure to particle number concentration (PNC) as indicator for UFP, ozone, particulate matter with diameters <10 µm (PM₁₀), <2.5 µm (PM_2.5) and 2.5–10 µm (PM_coarse), soot and nitrogen oxides (NO₂, NO_x) was measured in 2013/14 and individual concentrations at the participants’ residences were estimated by land use regression. We used generalised estimating equations adjusting for socio-demographic, lifestyle and clinical covariates to assess the association between annual average air pollution concentration and prevalence of T2D. Effect modifications were tested by use of interaction terms.

Results We analysed 9450 observations of 4217 participants aged 25 to 75 years at baseline. T2D prevalence increased from 4.4% at baseline to 9.9% at the second follow-up. Our results indicated an increased T2D prevalence in association with all air pollutants. Significant effect estimates were seen for PNC [odds ratio: 1.14 (95%-confidence interval: 1.03; 1.25) per 1958 particles/cm³ (interquartile range) increase], PM_coarse [1.15 (1.03; 1.29) per 1.4 µg/m³ increase] and NO_x [1.14 (1.02; 1.27) per 8.6 µg/m³ increase]. Effect estimates were higher for smokers, residents of the rural counties and participants with high CRP, whereas age, sex, obesity, physical activity, education, and a history of cardiovascular disease did not modify the estimates significantly.

Conclusion As one of the first studies investigating chronic exposure to ultrafine particles and T2D in a longitudinal setting, our results point towards a positive association highlighting the role of ultrafine particles within the complex mixture of ambient air pollution.