Urban green space, tree canopy, and prevention of heart disease, hypertension, and diabetes: a longitudinal study

Abstract

BackgroundWhile many studies suggest there are health benefits of urban green space, relatively few have explored potential for prevention of major non-communicable diseases. Those which have tend to rely on cross-sectional data that is vulnerable to reverse causation and also typically focus on total green space, rather than attempt to tease out which type of green space matters most; a key question among urban planners. The purpose of this longitudinal study was to examine whether urban green space in total, and tree canopy specifically, plays a protective role in prevention of heart disease, hypertension, and diabetes. MethodsIncident doctor diagnosed heart disease, hypertension and diabetes were measured in a residentially stable sample of 46 786 city-dwellers in the Sax Institute's 45 and Up Study (baseline 2006–09; follow-up 2012–15). The odds of incident outcomes were measured in association with total green space and tree canopy within 1·6 km road network buffers using multilevel models adjusted for confounding. These analyses were replicated to check for associations with prevalent outcomes. FindingsThe odds of incident heart disease (odds ratio 0·78, 95% CI 0·65–0·93), hypertension (0·83, 0·72–0·96), and diabetes (0·69, 0·54–0·85) were lower among people with ≥30% tree canopy, compared to 0–9% tree canopy. Evidence was also found to suggest lower odds of prevalent heart disease (0·85, 0·75–0·95), hypertension (0·87, 0·78–0·96), and diabetes (0·62, 0·52–0·75) with ≥30% tree canopy compared with 0–9% tree canopy. Total green space ≥30% compared to 0–4% was associated with lower odds of prevalent diabetes only (0·72, 0·52–0·98). InterpretationThis longitudinal study adds further support for urban greening, and restoration and conservation of urban tree canopy in particular, to be considered as a non-health sector-led strategy for non-communicable disease prevention. FundingThe Hort Frontiers Green Cities Fund and the National Health and Medical Research Council.