Urban greenness and related health effects

Abstract

Exposure to urban greenness has been linked to a wide range of health outcomes, including many non-communicable health conditions which are presently among the largest contributors to the global burden of disease, such as cardiovascular and metabolic diseases, as well as mental disorders. Half of the world’s population now lives in urban areas; often affected by health hazards such as pollutants and heat islands, and characterized by low levels of physical activity, inadequate diets, and decreased access to nature. The overarching aim of this thesis was to investigate associations between residential greenness and different health-related outcomes, including physical activity, adiposity measures and hypertension, as well as general and mental health, both regionally and internationally. In addition, we aimed to evaluate the potentially modifying role of other individual, contextual, and environmental variables, including sociodemographic, behavioral and socioeconomic factors, as well as air pollution, transportation noise and blue space.

We used data from the Stockholm Public Health Cohort (n=42 611), from 2010 and 2014, and the Stockholm Diabetes Prevention Program (n=5 126 and n=4 623, respectively) from 1992–2006, for three of the papers. The fourth paper was a meta-analysis including three cross-sectional surveys from southern Sweden, Spain, and the UK (N=50 220), conducted between 2012 and 2014. We assessed residential greenness exposure using the satellite-derived Normalized Difference Vegetation Index (NDVI) and land-use data. Outcome assessment was based on self-reported data from questionnaires, clinical examinations, and health registers.

Changing residential greenness exposure, because of moving, was inversely associated with walking/cycling. Both moving to a greener and to a less green area were associated with a decrease in exercise. Higher greenness exposure was associated with reduced increase in waist circumference and lower risk of central adiposity in women, but not in men. Exposure to low NDVI levels in combination with high NOx from road traffic and transportation noise as well as long distance to blue space were associated with increases in waist circumference in both sexes. Increased greenness exposure during 5 years preceding diagnosis was also a predictor of reduced hypertension risk. A more pronounced risk reduction associated with greenness exposure was observed for those exposed to road traffic noise ≥53 dB Lden or aircraft noise ≥45 dB Lden, respectively. Green and blue space measures were weakly associated with general and mental health in a meta-analysis of surveys from three countries, and with inconsistent patterns in each of the individual surveys.

In conclusion, our findings illustrate the complexity of the urban greenness-health relationship, and the importance of context and assessing the impact of other environmental exposures. Our results suggest a potentially mitigating role of greenness on negative health effects of environmental exposures, such as air pollution and transportation noise.