Trees and greenery are well known to bring multiple benefits to urban environments, but their positive effect on people’s mental and physical health is harder to quantify — something addressed by two recent studies.
Research by the University of Exeter Medical School’s European Centre for Environment & Human Health found that people who spend at least two hours a week in nature — town parks, woodlands, country parks and beaches — were significantly more likely to report good health and higher psychological well-being than those who do not.
Those who spent fewer than two hours in such environments reported no such benefits, though the study of nearly 20,000 people in England found it appeared not to matter whether the two hours were achieved in a single visit or over several shorter visits within the week. The correlation between such visits and positive health and well-being "peaked between 200 and 300 minutes per week with no further gain", the researchers found.
The 120-minute threshold applied to both men and women, to older and younger adults, across different occupational and ethnic groups, among those living in both rich and poor areas, and even among people with long-term illnesses or disabilities.
Environmental psychologist Dr Mat White, who led the study, says: "It’s well known that getting outdoors in nature can be good for people’s health and well-being, but until now we’ve not been able to say how much is enough."
He adds: "The majority of nature visits in this research took place within just two miles of home, so even visiting local urban green spaces seems to be a good thing. Two hours a week is hopefully a realistic target for many people, especially given that it can be spread over an entire week to get the benefit."
Professor Terry Hartig of Uppsala University in Sweden, a co-author of the research, adds: "The findings offer valuable support to health practitioners in making recommendations about spending time in nature to promote basic health and well-being, similar to guidelines for weekly physical health."
The research was published in the journal Scientific Reports, an imprint of Nature, and is based on data from Natural England’s Monitor of Engagement with the Natural Environment survey, claimed to be the world’s largest data source on people’s weekly contact with the natural world.
The Exeter study did not differentiate between different types of green space, wooded or not. But a recent Australian study suggests trees in particular can deliver public health benefits. Researchers at the University of Wollongong, New South Wales, found people have both a lower risk of developing psychological distress and better overall health if they have more trees within walking distance from their homes.
Having tracked the health of around 46,000 people aged 45 and older, they found those living in neighbourhoods with a tree canopy of 30% or more had a 31% lower chance of developing psychological distress and a 33% lower chance of rating their general health as "fair" or "poor" over six years (for comparison, the average urban tree canopy cover in England is 16%). But strikingly, urban green spaces with open grass rather than a tree canopy did not appear to produce this effect.
"Plain, flat grassy areas may not be particularly attractive for walking, which is an important form of social and physical recreation for older adults," the paper states.
The study’s lead author, Professor Thomas Astell-Burt, says: "Our results suggest the type of green space does matter and that protecting and increasing the urban tree canopy could potentially deliver significant community health benefits."
Publication of the findings coincides with a drive by New South Wales premier Gladys Berejiklian to plant a million trees across the greater Sydney area by 2022, stating: "Planting trees and creating new parks is just as important as building new roads, rail lines, schools and hospitals." Astell-Burt adds: "It’s great to see this in the New South Wales premier’s new priorities."
Fellow researcher, associate professor Xiaoqi Feng, suggests that while trees clearly provide shading and reduce city temperatures on hot days, other benefits are more subtle. "The vibrant colours, natural shapes and textures, the fresh aromas and rustling of leaves in the breeze all provide distraction and relief from whatever it was you might have been thinking about, or even stressing over," she says.
"Studies back this up. Walks through green space have been shown to reduce blood pressure, improve mental acuity, boost memory recall and reduce feelings of anxiety."
The paper was published in JAMA Network Open, an imprint of the Journal of the American Medical Association.