Nature exposure and health
Contact with nature is associated with physical and mental health benefits, including in urban green spaces. The evidence depends on the type and duration of exposure, and observational associations do not establish that nature itself caused better health.
Observed associations
Exposure to nature has been associated with lower cardiovascular mortality, reduced blood pressure, fewer allergies, better mental health and better self-reported general health. Psychological benefits are not limited to wild forests or mountains: similar benefits have been reported for urban green spaces.
A Danish study found that children with the lowest green-space exposure around their homes had up to a 55% higher risk of psychiatric disorders in adulthood, after accounting for urbanisation, socioeconomic status, parental age and family history of mental illness. Exposure was quantified using satellite images of Denmark from 1985 to 2013.
Duration and type of exposure
Spending more than two hours a week in nature was associated with a greater likelihood of good health and wellbeing, with no additional association reported beyond five hours. Weekly visits lasting at least 30 minutes were associated with less depression and high blood pressure.
In New York City, health benefits associated with nearby green space were greater for tree-covered areas than for grass-only areas. University students in the United States whose rooms overlooked green space performed better on attention tests. In another study, participants first completed a mentally fatiguing attention task, then viewed nature photographs, urban scenes or geometric patterns; only the nature-photograph group improved its attention scores.
Causation and possible pathways
Observational associations can reflect reverse causation: depression or high blood pressure may reduce time outdoors, rather than reduced nature exposure causing those conditions. The weekly-visit study included activity levels and body mass index in its analyses, but correlation still does not establish causation.
Vegetation can contribute to physical health by absorbing pollutant gases, including carbon monoxide, sulphur dioxide, nitrogen dioxide and ozone, as well as particulate matter, and by regulating temperature. Green space can also encourage physical activity, which reduces risks associated with sedentary living, including obesity, diabetes and mental health problems.
Practical implications
Potential health and cognitive benefits should be considered in public investment in providing, managing and enhancing green spaces. Regular weekly contact with nature is a practical recommendation drawn from this evidence.