The Equigenic Effect of Greenness on the Association between Education with Life Expectancy and Mortality in 28 Large Latin American Cities

Background: Recent studies highlight the equigenic potential of greenspaces by showing narrower socioeconomic health inequalities in greener areas. However, results to date have been inconsistent and derived from high-income countries. We examined whether urban greenness modifies the associations between area-level education, as a proxy for socioeconomic status, and life expectancy and cause-specific mortality in Latin American cities. Methods: We included 28 large cities, >137 million inhabitants, in nine Latin American countries, comprising 671 sub-city units, for 2012–2016. Socioeconomic status was assessed through a composite index of sub-city level education, and greenness was calculated using the normalized difference vegetation index. We fitted multilevel models with sub-city units nested in cities, with life expectancy or log(mortality) as the outcome. Findings: We observed a social gradient, with higher levels of education associated with higher life expectancy and lower cause-specific mortality. There was evidence of an interaction by greenness on the association between education and life expectancy (both sexes), cardiovascular diseases (CVD) mortality (in women), and violence-related mortality (in men). We observed an equigenic effect, with a narrower social gradient in greener areas, for violence-related mortality. Specifically, we found doubling magnitudes in the mortality reduction by education in areas with low greenness compared to medium-high greenness areas among men (16% [95% CI 0·80 to 0·88] vs 8% [95% CI 0·89 to 0·96] per 1 SD increase in area-level education). The equigenic effect was less pronounced in violence-related mortality among females and was not observed in the other outcomes. Interpretation: Our results confirm socioeconomic health inequalities in Latin American cities and show that the equigenic properties of greenspace vary by health outcome. Funding: Funding: Wellcome Trust (Grant 205177/Z/16/Z). Declaration of Interest: None to declare.