A team of researchers conducted a systematic literature review and meta-analysis for the purpose of synthesizing and quantifying evidence of the impact of greenspace on a wide range of health outcomes. Their search for relevant literature included five online databases and reference lists up to January 2017. Two of the authors, working independently, evaluated potential studies in relation to eligibility criteria set in advance. They identified 143 scientific studies meeting the inclusion criteria. The combined population of the studies exceeded 290 million people from 20 different countries. Included in the review were 103 observational studies and 40 interventional studies. Almost all of the articles (96%) were based on studies from the past 10 years; no papers prior to 1984 met the inclusion criteria, illustrating the recent, increasing interest in the topic.
Data analysis focused on how the health of people with little access to green spaces compared to that of people with the highest amounts of greenspace exposure. Greenspace was defined as “open, undeveloped land with natural vegetation as well as urban greenspaces, which included urban parks and street greenery”. While the review focused on a wide range of health outcomes and investigated over 100 different outcomes, it did not include mental health and communicable diseases.
Meta-analysis of the data showed that greenspace exposure was linked to statistically significant reductions in diastolic blood pressure, salivary cortisol (a physiological marker of stress), heart rate, and incidence of diabetes. Findings also indicated that exposure to greenspace reduces the risk of preterm birth, premature death, and high blood pressure. Some studies found that the association between greenspace exposure and positive health outcomes was stronger for people with low socioeconomic status and living in the most deprived communities than for people in more advantaged situations. This finding supports the idea that improving greenspace accessibility in deprived areas may help combat health inequalities.
This research indicates that people with higher levels of greenspace exposure are more likely to have good overall health. While a number of meta-analysis were judged to be of questionable study quality and did not include diverse populations, overall findings support the understanding that exposure to health-promoting environments (including natural environments) may be effective in preventing and helping to treat disease.
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