Greenness, Air Pollution, and Insulin Resistance in a Latin American Megacity: A Longitudinal Mediation Analysis of the ELSA‑Brasil Cohort

Studies examining the relationship between greenness and insulin resistance may elucidate the distal association between greenness and type 2 diabetes. The role of air pollution on this association remains unclear. We investigated whether air pollution mediated the association between greenness and insulin resistance, among non-diabetic participants ( N = 2715) from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) in São Paulo megacity, Brazil, followed-up for approximately 8 years (2008–2010, 2012–2014, 2017–2019). Neighborhood greenness (NDVI, in quartiles), air pollution (PM 2.5 and PM 10 ), and insulin resistance (HOMA-IR) were examined using mediation analysis, allowing for exposure-mediator interaction. Total, natural direct, and natural indirect effects were estimated, using mixed-effects models, stratified by the neighborhood socioeconomic status (NSES) and adjusted for individual age, sex, education and income. In PM 10 analysis for participants from low NSES, higher neighborhood greenness was associated with lower insulin resistance, in a dose-response pattern, as indicated by the total ( β = −0.49, 95% CI −0.91, −0.05; β = −0.20, 95% CI −0.54, 0.16; and β = −0.07, 95% CI −0.38, 0.27, for the 4th, 3rd, and 2nd NDVI quartile vs 1st quartile, respectively) and natural direct effects ( β = −0.59, 95% CI −1.06, −0.09; β = −0.32, 95% CI −0.67, 0.03; and β = −0.05, 95% CI −0.37, 0.27, for the 4th, 3rd, and 2nd NDVI quartile vs 1st quartile, respectively). The natural indirect effect indicated no mediation by PM 10 . Similar results were found for the PM 2.5 analysis. Greenness was associated with lower insulin resistance among adults living in low NSES areas. However, no evidence of air pollution mediation was found. These results suggest that greater neighborhood greenness may be associated with better cardiometabolic health in socioeconomically disadvantaged areas.