The greener your city, the longer you live: Lancet study
Even a middle-schooler can tell you the benefits of having more plants around today. We’ve all been taught of the essential role greenery plays in our lives from a very young age. But even so, year by year, we see fewer trees by the road, parks being converted into parking lots and forests disappearing in favour of metro stations.
A study published in the Lancet last week showed an association between access to green spaces and lower all-cause mortality (death from all causes during a given period). A meta-analysis of nine longitudinal studies covering over 8 million individuals across seven countries showed that a 10% increase in greenery led to an average 4% reduction in premature mortality.
The first meta-analysis of the impact of green space on mortality
The authors cautioned against drawing simplistic conclusions from the study; longitudinal studies can illustrate patterns and linkages but cannot ascertain causality. Further, the impact of the environment on health is complicated to understand given the vast number of variables influencing health outcomes. Having said that, this study is worth noting since it is the first meta-analysis of the impact of green spaces on mortality. Since it focuses mainly on developed countries (China is the only developing nation involved in the analysis), covariates such as socio-economic status have been controlled for. The study aims to inform urban planning policy given that half of the world is now urban.
The overall epidemiological evidence suggests that exposure to green space could have health benefits like greater physical activity, lower levels of stress, better air quality, biodiversity and lesser traffic noise. Green spaces have also been associated with better mental health, reduction in cardiovascular disease and better pregnancy outcomes.
NDVI (normalized difference vegetation index) was used as the exposure index for green spaces. The index analyzes remote sensing measurements by comparing radiation that is reflected with radiation that is absorbed by vegetation. The scale ranges from -1 to 1 wherein -1 indicates water bodies, 0 indicates no vegetation and 1 reflects the highest amount of vegetation. The study found a significant inverse relationship between an increase in surrounding greenness per 0·1 NDVI in a buffer zone of 500 m or less and the risk of all-cause mortality. This means that an increase in vegetation within 500 m of residence has improved long term health outcomes.
The link between greenery and health
Both health determinants and biological pathways have been attributed to the impact of the outdoors on health outcomes. Green spaces facilitate physical activity and are less likely to be polluted and noisy. A study based in India showed that vegetation belts reduce the harmful effects of traffic noise which is linked to cardiovascular disease, stress and sleeping issues. Another study found changes in immune responses, including the presence of anticancer proteins with exposure to forests.
Impact on city planning
While the study does not make any claims of causality and acknowledges its limits, some pointers can be taken from it. About 20-30% of every city should be covered with green spaces, the authors commented. According to the forest survey of India, out of the big cities, Mumbai has the greatest forest cover by area at 22% whereas Kolkata has the lowest at 0.54%. As our cities grow bigger, planners will do well to give green spaces the attention they deserve.
For more information, please read our article on Sleep Disorders.
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Updated Date: Dec 10, 2019 13:49:43 IST
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