Abstract
There is evidence that access to green spaces have positive effects on health, possibly through beneficial effects on exercise, air quality, urban heat islands, and stress. Few previous studies have examined the associations between green space and mortality, and they have given inconsistent results. This ecological study relates green space to mortality in Hong Kong from 2006 to 2011. The Normalized Difference Vegetation Index (NDVI), a measure of green space coverage, was measured for 199 small geographic areas in Hong Kong. Negative Binomial Regression Models were fit for mortality outcomes with NDVI, age, gender, population density, and area-level socio-economic variables as predictors, with Generalized Estimating Equations used to control for within-cluster correlation. An interquartile range (0.44 units) higher NDVI was significantly associated with lower cardiovascular (relative risk (RR) = 0.88, 95% confidence interval (CI) = 0.80, 0.98) and diabetes (RR = 0.72, 95% CI = 0.60, 0.92) mortality, and non-significantly associated with lower chronic respiratory mortality (RR = 0.90, 95% CI = 0.79, 1.02). Associations were stronger for males and low-income area residents. Lung cancer mortality had no significant association with green space. Better provision of urban green space, particularly in low-income areas, appears to have potential to reduce mortality in densely-populated Asian cities.
Highlights
Green space is defined as areas of grass, trees, or other vegetation set apart for recreational or aesthetic purposes [1], and examples of green space include national parks, forests, recreation areas, community gardens, green belts, and city parks
Hong Kong is a high-income country, it has a very high level of income inequality [20], and is one of the most densely populated places in the world [21]. In this Hong Kong-based ecological study, we examined the association between area-level green space, population density, and several socioeconomic indicators, with all non-accidental causes of mortality and cause-specific mortality from cardiovascular diseases, chronic respiratory diseases, diabetes, and lung cancer
The results show that the protective association between Normalized Difference Vegetation Index (NDVI) was considerably stronger for males than for females for all-natural and CVD mortality, and slightly stronger for diabetes and chronic respiratory mortality
Summary
Green space is defined as areas of grass, trees, or other vegetation set apart for recreational or aesthetic purposes [1], and examples of green space include national parks, forests, recreation areas, community gardens, green belts, and city parks. Hong Kong is a very densely populated city with over seven million people and limited land availability. Longevity in a densely populated city [13] and is associated with a lower odds of having any form of impaired glucose regulation [14]. The few studies examining associations between area-level green space and mortality have given inconsistent results. There are many factors that could influence these results and explain the inconsistencies between studies including differences in local climate, nature, accessibility of green space, and individual characteristics of the populations, such as socioeconomic status and personal habits. Two studies from the United Kingdom found that living in areas with more green space was associated with health and lower mortality for all cause [4], circulatory [4,15], and respiratory mortality [15], but not lung cancer mortality [15], while a similar study from New
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