Association Between Long-term Exposure to PM2.5 and Incidence of Type 2 Diabetes in Taiwan: A National Retrospective Cohort Study

BACKGROUND: Long-term exposure to fine particulate matter (PM with an aerodynamic diameter ≤2.5 µm; PM2.5) contributes to an elevated incidence of type 2 diabetes (T2D) in North America and Europe, but there is limited empirical evidence for Asian countries. This study determined the association between and the exposure-response relationship for PM2.5 and the incidence of T2D in Taiwan. METHODS: This retrospective cohort study was conducted for the years 2001-2012. Health information, including age, sex, health insurance premium, type of occupation, medication, and disease status, was retrieved from the Longitudinal Health Insurance Database 2000. Monitoring data for PM2.5 came from the Environmental Protection Administration of Taiwan, and Land-use Regression modeling was used to approximate participants' long-term exposure to PM2.5. Cox proportional hazards models with a generalized estimating equation to account for the correlation within the locations of the medical facilities were used to estimate the association between exposure to PM2.5 and the incidence of T2D, adjusting for the potential confounders. We also examined effect modification of sex, age, hyperlipidemia, and National Health Insurance premium for the association. RESULTS: Forty-eight thousand six hundred eleven new cases of diabetes were identified among 505,151 eligible participants, with the median follow-up of 12 years. Positive associations were identified between long-term exposure to PM2.5 exposure and the incidence of T2D. An increase of 10 μg/m PM2.5 was associated with an 11.0% increase in the risk of contracting diabetes (95% confidence interval = 8.0%, 13.0%). The results show that there is an almost linear relationship between exposure to PM2.5 and the incidence of T2D. Sex, age, hyperlipidemia, and National Health Insurance premium acted as effect modifiers of the association between diabetes incidence and levels of PM2.5 exposure in Taiwan. CONCLUSIONS: In the population in Taiwan, long-term exposure to PM2.5 increases the risk of incidence of T2D by 11%. This effect is more pronounced in elderly male patients who exhibit hyperlipidemia and in individuals who have a lower insurance health insurance premium.