Associations of greenness with diabetes mellitus and glucose-homeostasis markers: The 33 Communities Chinese Health Study

Background Residing in greener places may be protective against diabetes mellitus (DM) but evidence is scarce and comes mainly from developed countries. Objectives To investigate associations of residential greenness with DM prevalence and glucose-homeostasis markers in Chinese adults and whether these associations were mediated by air pollution, physical activity, and body mass index. Methods In 2009, a total of 15,477 adults from the cross-sectional 33 Communities Chinese Health Study provided blood samples and completed a questionnaire. We considered fasting and 2-h glucose and insulin concentrations, as well as the homoeostasis model assessment of insulin resistance and β-cell function, as glucose-homeostasis markers. DM was defined according to the American Diabetes Association's recommendations. Residential greenness was estimated by two satellite-derived vegetation indexes – Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI). Nitrogen dioxide and particulate matter ≤2.5 μm were used as air pollution proxies. Associations were assessed by two-level adjusted logistic and linear regression models. Results A 0.1-unit increase in NDVI500 m and SAVI500 m was significantly associated with lower odds of DM by factors of 0.88 (95% Confidence Interval 0.82–0.94) and 0.80 (0.72–0.90), respectively. Higher greenness was also significantly associated with lower fasting and 2-h glucose levels, 2-h insulin level, as well as lower insulin resistance and higher β-cell function. Air pollution and body mass index significantly mediated 6.9–51.1% and 8.6–78.7% these associations, respectively, while no mediation role was observed for physical activity. Conclusions Higher residential greenness appears to be associated with a lower prevalence of DM. This association might be due to glucose and insulin metabolism and pancreatic β-cell function. Lower levels of air pollution and body mass index can be pathways linking greenspace to diabetes