Combined exposure to multiple air pollutants and incident ischemic heart disease in individuals with and without type 2 diabetes: A cohort study from the UK Biobank

Background: Air pollution and type 2 diabetes (T2D) are both associated with an increased risk of ischemic heart disease (IHD). Little is known about the combined effects of multiple air pollutants on IHD risk, especially among individuals with T2D. We sought to assess the association of combined exposure to multiple air pollutants with incident IHD and examine the modification effect of T2D.Methods: This study included 388 780 individuals (20 036 individuals with T2D) free of cardiovascular disease and cancer from the UK Biobank. The combined exposure to multiple air pollutants, including particulate matter (PM) with diameters <= 2.5 mu m (PM2.5), PM with diameters between 2.5 and 10 mu m (PMcoarse), PM with diameters <= 10 mu m (PM10), nitrogen dioxide (NO2), and nitrogen dioxides (NOx), was assessed by creating a weighted air pollution score (APS), with a higher APS representing a higher level of air pollution exposure. Hazard ratios (HR) and 95 % confidence intervals (CI) for incident IHD were assessed by multivariable-adjusted Cox proportional hazard models.Results: During a median of 12.9 years of follow-up, 27 333 incident IHD cases were observed. Compared with the lowest tertile of the APS, the multivariable-adjusted HR (95 % CI) of IHD risk for the highest tertile was 1.13 (1.03-1.23) among individuals with T2D, while the HR was 1.06 (1.03-1.10) among individuals without T2D. Additionally, the associations between APS and IHD incidence showed a linear relationship among individuals with T2D (nonlinearity: P = 0.37), whereas a non-linear relationship was observed among individuals without T2D (nonlinearity: P = 0.02). For the joint analysis, individuals in the highest tertile of APS and with T2D had a 54 % higher risk of IHD compared to individuals in the lowest tertile of APS and without T2D, with a significant additive interaction (P (interaction) < 0.01). The proportion of relative excess risk was 17 % due to the interaction in categorical analyses. Conclusions: The combined exposure to multiple air pollutants has been associated with an elevated risk of incident IHD, and the association is more pronounced among individuals with T2D.