Time in nature reduces stress and cuts risk factors for developing depression. So why aren’t doctors writing prescriptions for it?

For all of human history, more people have lived in rural areas than in cities.

We’re now at a tipping point where half of the world’s population lives in cities, and the percentage is expected to reach 70 percent in 2050.

Many scientists are beginning to look at how this shift is affecting our health in general, and our mental health in particular.

“It’s really the blink of an eye that we’ve been living in urban areas. It’s not what we’re evolutionarily adapted to,” said Greg Bratman, a Ph.D. candidate in conservation biology at Stanford University who is the lead author of a paper published in the Proceedings of the National Academy of Sciences (PNAS).

It concludes that nature walks may help prevent or manage depression and anxiety.

Healthy people who took a 90-minute walk in a natural area were less engaged in negative rumination after their exercise than those who walked along a city street, according to the study.

The researchers saw the drop in rumination on questionnaires and on brain scans of the subgenual prefrontal cortex, where that kind of thinking is believed to occur.

Rumination, or focusing on negative thoughts of self, is a risk factor for the onset of depression.

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By now, it’s fairly well known that nature can improve health outcomes.

“The evidence has been accumulating and we can feel pretty confident of the results at least in a general sense,” said Susan Clayton, a Whitmore-Williams professor of psychology at The College of Wooster in Ohio. Clayton was not involved with the PNAS study.

There’s quite a bit of research to support the idea that experiences in nature contribute to our well-being.

In the 1980s, a study found that hospital patients who had a view of a tree from the windows in their rooms needed less pain medication and recovered faster than their peers who saw a brick wall.

A 2001 study found that public housing residents with nearby trees and grass coped with major life issues more effectively than those whose homes were surrounded by concrete.

Poor people with green views were also more likely to have babies with healthier birth weights, according to a separate study.

There are also findings linking time in nature to better working memory in healthy adults and even reduced dementia in those with Alzheimer’s disease.

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Healthcare costs dominate personal and national budgets, in large part because people in the United States generate over 4 billion retail prescriptions a year. Antidepressants are among the top three types of drugs prescribed.

But Bratman cautioned that more research was needed before doctors could prescribe time in nature. The brain scans were a first step, he said.

Cities also want to know how big their nature parks need to be and if they need any specific features, according to Clayton.

The biggest push may be getting people to take advantage of green spaces beyond just enjoying the view.

“People like nature. They know in a general way that it’s good for them to relax, but they don’t make that final statement that if I go for a walk in the park, that might be better than taking an antidepressant or an aspirin,” Clayton said.

She added: “There are lots of ways in which we don’t do things that we know are good for us, and it’s often as simple as what we see other people doing.”

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