Associations of residential green space with incident type 2 diabetes and the role of air pollution: A prospective analysis in UK Biobank

Background: Green space is a newly modifiable environmental factor which would bring health benefits, and identify-ing potential pathways is important to better promote public health. Nowadays, limited evidence is available on resi-dential green space and risk of incident type 2 diabetes (T2D). To evaluate the longitudinal association between residential green space and incident T2D, and further illustrate the role of air pollution, we conducted a prospective analysis in UK Biobank.Methods: Incident cases of T2D were ascertained through medical linkage of hospital admissions. Residential green space indicated by percentage of green space at 300 m buffer was estimated using land use data. Annual average air pollution was modelled using Land Use Regression model. Cox proportional hazard regression models were used to determine the association between the exposure and incident T2D. Effect modification of air pollution was assessed using log-likelihood tests. Casual mediation analysis including interaction of green space and air pollution was used to quantity pure natural indirect effect of air pollution.Results: Of 379,238 participants at baseline, 15564 incident T2D cases were identified with 12.4 years of follow-up. In main models, individuals who exposed to residential green space at 300 m buffer in high level (>= 75 %) had 14.4 % (95 % CI: 8.0 %, 20.3 %) lower risk of incident T2D compared with those in low level (<25 %). This association was modified by NO2, with green space indicating higher protective effect in low NO2 level (P interaction = 0.098). PM2.5 had a high mediation effect of 37.0 % in the association.Conclusion: Elevated residential green space level was associated with lower risk of incident T2D, and air pollution played an important role in this association. These findings would contribute to policy making and healthy city construction to take air pollution into consideration while planning green space, which would maximize public health benefits.