Urban Greenness and Your Health

More biodiversity, birds, butterflies, better health

More trees, greater greenness, greater well-being

Natural environments and green spaces can improve several aspects of human health, including better mental health, diminished allergies, and reduced mortality risk. The biophilia hypothesis proposed by the late E. O. Wilson asserts that humans have an innate affinity for the natural world, which might cause humans to favor biologically diverse environments. Biodiversity refers generally to the richness of species and types of natural communities in an area. A review of 19 studies by Belgian researchers found limited evidence linking biodiversity to aspects of human health, primarily psychological well-being. In particular, a plurality of studies showed positive correlations between perceived bird species richness, habitat diversity, butterfly species richness, but not plant species richness. Perhaps humans can perceive differences among birds, habitat types, and butterflies more readily than among plants.

Most studies that find greater contact with the natural environment predicts better health and well-being evaluate contact in terms of the proximity of natural areas.  A recent study took a different tact. Researchers uses cross-sectional data from 2014-2016 for 19,806 participants in the Monitor of Engagement with the Natural Environment, a representative sample of English residents. Direct contact with relatively natural areas was calculated as the self-reported number of minutes per week spent in natural areas (parks, green space, beaches, etc.) multiplied by the number of such weekly visits. Participants rated their own health and well-being on five-point scales.

After accounting for confounding factors, participants who had at least 120 minutes per week of contact with nature had significant 59 and 23 percent higher likelihoods of reporting good health or high well-being. The benefit of contact with nature plateaued at 300 minutes per week. These results accounted for socio-economic status, age, and health status. The benefit occurred regardless of the length (short or long) of the individual periods of nature contact. The magnitudes of the health and well-being benefit were comparable to those of other health-related factors, including socio-economic status or physical activity status. The benefit of contact with nature may not solely reflect increased physical activity; rather, it may reflect an innate human need for nature.

Emerging evidence suggests that green spaces in urban environments promotes better human health and well-being. But many studies rely on self-reports of health that are subject to bias. A study from Leipzig, Germany, used a more objective measure of mental health: prescriptions for antidepressants. Research subjects included 9,764 Leipzig residents who participated in the LIFE-Adult Study. These subjects provided data for antidepressant use between April 2011 and November 2014. The City of Leipzig provided data showing the locations and species of street trees. Researchers calculated and categorized street tree density (low, medium, high) in zones ranging from 100 to 1,000 meters around the house of each subject. Within the 100 meter zone, researchers found a marginally significant negative correlation between street tree density and likelihood of an antidepressant prescription. Neither density nor species predicted antidepressant prescription farther than 100 meters from a subject’s home. Notably, subjects with low socio-economic status who lived in a 100-meter zone with high tree density had a lower probability of being prescribed an antidepressant drug. These results suggest that daily close proximity to abundant street trees might improve people’s mental health, especially those of low socio-economic status.

Numerous studies link increased urban greenness with positive health outcomes and lower prevalence of cardiovascular disease. Most studies, however, involve populations in higher-income countries. What about lower-income countries, such as China? Researchers in China and Australia recruited 24,845 participants from 33 communities in three large cities in heavily urbanized Liaoning Province in northeastern China. Cardiovascular disease was self-reported, while cardiovascular disease-related metabolic factors were determined from blood samples and from bodily measures. Urban greenness was determine from satellite imagery using two standard techniques, NDVI and SAVI (which produced almost identical results).

Cross-section analyses showed that higher values of both NDVI and SAVI predicted lower prevalence of cardiovascular disease. An increase of one interquartile range in NDVI greenness within a radius of either 500 or 1,000 meters of a community predicted 27 and 21 percent lower odds of cardiovascular disease. In addition, the presence of cardiovascular-related metabolic factors, such as hypertension, type 2 diabetes, and excess blood fats, affected the association between urban greenness and cardiovascular disease. Perhaps greater urban greenness motivates residents to engage in more healthy lifestyles, such as increased physical activity. Increasing urbanization may lead to reduced greenness and poorer health for urban residents.

If this blog post tickled your fancy, you might check out two books that address links between urban green spaces and human health. The Nature Principle – Reconnecting with Life in a Virtual Age by Richard Louve (2012) and The Nature Fix – Why Nature Makes Us Happier, Healthier, and More Creative by Florence Williams (2017). Both books offer lively and interesting reading. Spending more time in nature, such as at your neighborhood park, will likely improve your health and well-being. If you need an excuse to spend more time in nature, here it is.

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