Long-term exposure to ambient PM2.5 leads to increased risk of Type 2 diabetes in urban Delhi and Chennai, India

Abstract

BACKGROUND AND AIM: India has high levels of ambient air pollution and a high burden of cardiometabolic disease. However, there is a lack of detailed exposure assessment and longitudinal studies on health impacts of ambient PM2.5. We studied the association between ambient PM2.5 with fasting plasma glucose (FPG), glycosylated haemoglobin (HbA1c) and incident Type 2 diabetes mellitus (T2DM) in the CARRS cohort (n=12066) in Delhi and Chennai, India, over 7 years of follow-up (median years of follow-up = 4.84 years). METHODS: Long-term exposure to PM2.5 was measured using daily predictions from a hybrid ensemble averaging based model. FPG and HbA1c were assessed at three time points, and T2DM was defined as FPG≥126mg/dl, or HbA1c≥6.5%, or self reported physician diagnosed diabetes, or being on medication for diabetes. Associations between PM2.5 and glycemic markers were assessed using longitudinal mixed effects models while incident T2DM was analyzed using Cox proportional hazard models. RESULTS:Median annual exposure at baseline was 41.14 μg/m3 (interquartile range, 38.70-43.35) and 92.08 μg/m3 (interquartile range, 87.60-95.74), in Chennai and Delhi respectively. For interquartile range(IQR) increase in annual exposures, we observed 2.54 mg/dL(95% CI:1.36-3.72) and 3.56 mg/dL(95% CI:1.16-5.96) increase in FPG at Chennai and Delhi respectively, after adjusting for covariates. The IQR differences in 2 years of exposure increased the risk of incident T2DM by 1.11(95% CI:1.03-1.19) times in Delhi and by 1.24(95% CI: 1.02-1.50) times in Chennai. Using a propensity score analysis, marginal hazard ratios for IQR change in 1 year, 1.5 years and 2 years of exposure were 4.1(95% CI:1.5-11.2), 5.6(95% CI:2.5-12.5) and 6.1(95% CI:2.5-14.8), indicating a dose-response rise in risk with continued long-term exposure. CONCLUSIONS:Our findings demonstrated the effect of a wide range of PM2.5 exposure on the risk of Type 2 diabetes, thus emphasizing the need to mitigate ambient air pollution for health benefits. KEYWORDS: Particulate matter, Long-term exposure, Obesity and metabolic disorders, Environmental epidemiology