Living near a green space — whether an urban park or other area of open, undeveloped land with natural vegetation — is associated with a wide range of health benefits, according to British researchers.

The researchers did a systematic review and meta-analysis of 143 previous studies conducted in 20 countries, including the United States, the United Kingdom, France, Spain, Australia and Japan. All the studies examined whether access to green spaces enhanced human health, although most focused on a specific health outcome, such as obesity, blood pressure or birthweight.

The British researchers decided to take a deeper dive into those studies to get a broader picture of what the research said about natural environments and their effect on our mental and physical health.

“We found that spending time in, or living close to, natural greenspaces is associated with diverse and significant health benefits,” said Caoimhe Twohig-Bennett, the review’s lead author and a graduate student at the University of East Anglia, in a released statement.

Those benefits included a reduced risk of type II diabetes, heart disease, preterm birth and premature death. People living nearer to nature also tended to sleep longer, to have lower levels of stress and to report being in good health. 

“One of the really interesting things we found is that exposure to greenspace significantly reduces people’s levels of salivary cortisol — a physiological marker of stress,” Twohig-Bennett added.

Possible explanations

The reasons for the relationship between nature and well-being are unclear, but several hypotheses have been proposed, as Twohig-Bennett and her co-author, environmental scientist Andy Jones, explain in their paper.

Access to natural and green areas may promote health by providing more opportunities for physical activity. (Interestingly, some research has found that exercising in a green environment is more beneficial than doing the same exercise in an indoor gym.)

Public green spaces also promote social interaction, which can contribute to an improved sense of well-being. And they expose people to sunlight, which may enhance mood and counteract seasonal affective disorder. 

There is also the “old friends” hypothesis, which proposes that the use of greenspace “increases exposure to a range of micro-organisms, including bacteria, protozoa and helminthes, which are abundant in nature and may be important for the development of the immune system and for regulation of inflammatory responses,” Twohig-Bennett and Jones write.

Japanese researchers have found that when we breathe in organic compounds called phytoncides, which are released by trees for protection against insects, our natural killer cells increase in number and activity. Natural killer cells are white blood cells that help identify and destroy cells infected with tumors or viruses. 

Shinrin-yoku, or “forest bathing” — spending time walking, sitting or lying down in forests — is a popular practice in Japan.

Cautions and implications

A meta-analysis is only as good as the studies it includes. This meta-analysis included mostly observational studies, which can’t prove a cause-and-effect relationship between greenspaces and enhanced well-being. Indeed, only 40 of the 143 studies were interventional, and 27 of those looked specifically at the association between shinrin-yoku and various health outcomes in Japan. Those studies’ findings may not be applicable to other populations.

There’s also the possibility that the studies’ findings may be explained by socioeconomic factors. As background information in the study notes, low-income neighborhoods tend to have fewer parks and other green spaces. The people who live near green spaces may, therefore, be healthier not because of the green spaces but because of their higher incomes. Having a higher income is a major determinant of better health. 

Yet, as Twowig-Bennett and Jones also point out, income-related health inequalities have been found to be lower in greener neighborhoods. 

“Greenspace may be currently overlooked as a resource for health and as part of a multi-component approach to decrease health inequalities,” they stress.

The researchers would like to see doctors and other health care professionals encourage their patients to spend more time in green, natural environments. 

They also hope their research “will inspire people to get outside more and feel the health benefits for themselves,” said Twohig-Bennet. 

One of their strongest messages, however, is aimed at the people who decide how our living environments are structured.

“Hopefully our results will encourage policymakers and town planners to invest in the creation, regeneration, and maintenance of parks and greenspaces, particularly in urban residential areas and deprived communities that could benefit the most,” Twohig-Bennet said.

FMI: You’ll find an abstract of the review on the website for the journal Environmental Research, but the full paper is behind a paywall.