Getting away from it all in the great outdoors has been a proven panacea for generations of city-dwellers, but a new study has quantified how access to nature could be a vital component in our overall mental health.

With more and more of us living in urban areas, researchers from Stanford University in the US wanted to investigate why urbanisation is associated with greater incidences of mental illness. In a controlled experiment, they looked at whether exposure to nature could influence depression levels and specifically 'rumination': repetitive thoughts focused on negative aspects of the self.

The researchers took two groups of participants and led them on 90-minute walks through two very different kinds of environments. One group walked across a grassland area populated with oak trees and shrubs, while the other group walked along the side of a heavily trafficked four-lane highway.

By performing brain scans on the walkers before and after the expedition, the team found that neural activity in the subgenual prefrontal cortex - the area of the brain that's active during rumination - had decreased in the volunteers who explored the natural environment. Their experience was consistent with this finding, with the group reporting that they found themselves ruminating less during the walk.

Those who trekked along the side of the road, on the other hand, demonstrated no changes in their neural activity, or in their self-reporting on rumination, suggesting that nature experiences can have a discernable, positive impact on our brains' emotional regulation.

"These results suggest that accessible natural areas may be vital for mental health in our rapidly urbanising world," said Gretchen Daily, a co-author of the study, in a release. "Our findings can help inform the growing movement worldwide to make cities more liveable, and to make nature more accessible to all who live in them."

The research could be incredibly important for the way urban environments and populations are managed in the future. Already half the world's population lives in cities, and the proportion of city-dwellers is expected to increase to 70 percent of the world's population by 2050.

With urban settings enveloping most of humanity within the very near future, it's vital that more work be done to counteract the negative psychological effects of residing in what are essentially unnatural living spaces.

When compared to rural folk, people living in cities have a 40 percent higher risk of mood disorders and a 20 percent higher risk of anxiety disorders. They're also twice as likely to develop schizophrenia.

With these sorts of despairing statistics in mind, 'getting away from it all' is becoming more than just a nice way to spend the weekend. It could prove an essential strategy to help maintain our psychological health in the 21st century.

"We want to explore what elements of nature - how much of it and what types of experiences - offer the greatest benefits," Daily said.

The research is published in Proceedings of the National Academy of Science.