Association between short-term ambient NO2 and type 2 diabetes outpatient visits: a time series study in multi-city, China

As a common chronic disease, type 2 diabetes mellitus (T2DM) and its complications not only jeopardize the health of patients but also impose a heavy economic burden on society and patients’ families. Nevertheless, there is a scarcity of evidence regarding the effects of nitrogen dioxide (NO₂) on T2DM. In our study, daily data for T2DM outpatients, air pollutants and meteorological factors from January 1, 2018, to December 31, 2020 were collected in three cities: Dingxi, Tianshui and Longnan, an inland province of northwest China. Generalized additive model (GAM) with quasi-Poisson regression combined with the Distributed Lag Non-linear Model (DLNM) were employed to assess the associations between NO₂ and daily T2DM outpatients, as well as their lag effects in various cities. We also stratified by gender, age, and season. The results from DLNM revealed that NO₂ was significant positively associated with the increase of the number of outpatient visits for T2DM at individual single-day and all cumulative lag days in three cities, with the largest Relative Risk (RR) at lag05, lag05 and lag07 [RR = 1.106 (95%CI: 1.045,1.171) for Dingxi, RR = 1.095 (95%CI: 1.047,1.146) for Tianshui and RR = 1.015 (95%CI: 1.015,1.138) for Longnan]. Stratified analysis of gender, age, and season suggested that the harmful effect of NO₂ was greater for males, young people (< 65 years old), and the cold season. In brief, ambient NO₂ was associated with the increase in the number of outpatient visits for T2DM in three cities. Our findings suggest that the role of exposure to NO₂ in T2DM pathogenesis should be further investigated in China.