Green space exposure and type 2 diabetes mellitus incidence: A systematic review

Introduction: Epidemiological studies have suggested that exposure to green spaces is associated with a lower prevalence of diabetes. The aim of this systematic review was to summarize the evidence on green spaces and diabetes mellitus II (T2DM) in longitudinal studies. Methods: We searched PubMed, SCOPUS, Web of Science (WoS)/Core Collection, WoS/MEDLINE, and EMBASE until February 2023. We included cohort studies that assessed the incidence of T2DM according to the level of exposure to green spaces. Two authors independently performed study selection, data extraction, and analysis of risk of bias. No meta-analysis was performed due to clinical heterogeneity between studies. Results: We included 13 cohort studies with a sample size ranging from 1700 to 1 922 545 participants. Studies presented different ways of defining (quartiles, percentages) and measuring (tools, buffers) green spaces. Similarly, the definition of T2DM was heterogeneous (self-reports, medical records, clinical criteria). Twelve studies showed that individuals with higher exposure to green spaces had a decreased incidence of T2DM. Out of these 12 studies, 10 revealed statistically significant differences. All studies were of high methodological quality, except for one. Conclusion: Our findings suggest that exposure to green space could be a protective factor for the development of T2DM. Promoting policies to preserve and increase green space could help to reduce T2DM at the community level. More standardization of green space exposure definition is needed in studies on green space and T2DM.