The built environment and its association with type 2 diabetes mellitus incidence: A systematic review and meta-analysis of longitudinal studies

This study aimed to systematically review longitudinal studies examining associations between the incidence of type 2 diabetes mellitus (T2DM) and built environmental factors. This review adhered to the 2020 PRISMA guidelines. Longitudinal studies examining associations between T2DM incidence and built environmental features were eligible. Built environment constructs corresponded to the following themes: 1) Walkability – factors such as sidewalks/footpaths, crosswalks, parks, and density of businesses and services; (2) Green/open space – size, greenness, and type of available public outdoor spaces; (3) Food environment – ratio of healthful food outlets (e.g., greengrocers, butchers, supermarkets, and health food shops) to unhealthful food outlets (e.g., fast-food outlets, sweet food retailers, and convenience stores). Five databases (e.g., Medline) were searched from inception until July 2023. Qualitative and quantitative synthesis were used to summarise key findings, including a meta-analysis of adjusted Hazard Ratios (aHR). Of 3,343 articles, 16 longitudinal studies from seven countries, published between 2015 and 2023, involving 13,403,902 baseline participants (median of 83,898), were included. In four of the five studies, unhealthful food environment was significantly associated with higher incident T2DM. Five of seven greenspace studies and two of four walkability studies showed that greater greenery and greater walkability were statistically significantly associated with lesser incident T2DM. In pooled analyses, greater T2DM incidence was associated with unhealthful relative to healthful food environments (pooled HR: 1.21; 95% CI: 1.04, 1.42), and T2DM incidence was inversely associated with green/open space environments (pooled HR: 0.82; 95% CI: 0.74, 0.92). Greater walkability was associated with a slight 2% lesser incidence of T2DM (pooled HR: 0.98; 95% CI: 0.98, 0.99). This review underscores consistency in the nature of associations between built environment features related to T2DM. We observed statistically significant inverse or “protective” associations between T2DM and walkability and healthful food environments. These results support calls for policies and guidelines that promote healthful food environments and walkability.