Roughly half of the world’s population lives in urban areas, far removed from the natural environment. Evidence indicates that people who live in urban areas are at greater risk for mental health disorders, such as depression. Findings from a new study suggest that walking in nature reduces ruminative thinking and decreases activity in parts of the brain associated with mental illness.

Ruminative thinking – dwelling on ideas (especially stressors) to excess – is a common feature of mental illness. Rumination can set in motion a cascade of hormonal and physiological responses that harm mental and physical health. A major player in the body’s response to rumination is a biological pathway that starts in the brain’s hypothalamus with the release of corticotrophin-releasing hormone, which drives the stress hormone system and has a direct effect on many parts of the body, including the brain, gut, and DNA.

Spending time in nature is associated with a variety of beneficial effects on mental and physical health. For example, some research indicates that walking in forested areas, sometimes referred to as “forest bathing,” improves immune function, likely due to beneficial bioactive compounds produced by trees and inhaled by walkers. Other research has identified dose-dependent improvements in health following natural experiences.

The study involved 38 mentally healthy men and women living in a large urban area. Half of the participants took a 90-minute walk in a natural area where native plants, animals, and birds were in abundance. The other half took a 90-minute walk in an urban area where there were busy streets and heavy traffic. To rule out any physiological effects of exercise on brain health and function, both groups wore monitors to measure their heart rate and respirations. After their respective walks, participants underwent magnetic resonance imaging (MRI) studies of their brains, with emphasis on the subgenual prefrontal cortex, an area of the brain involved in emotional regulation and reward mechanisms. They also completed a questionnaire in which they rated their ruminative tendencies.

The MRI studies revealed that after the participants walked in a natural area, their subgenual prefrontal cortex showed less activity. Those who walked in the urban area showed no changes in this region of the brain. Participants who walked in the natural area also reported less ruminative thinking after the walk, but those who walked in the urban area did not. The monitors revealed that the walks were equal in distance and exerted no physiological effects on the walkers.

These findings suggest that spending time in the natural environment benefits brain health and reduces ruminative thinking, underscoring the importance of public health measures to increase natural spaces within urban areas. If natural areas are not easily accessible, meditation offers another means of reducing ruminative thinking. Learn more about the benefits of meditation in this episode featuring Dr. Rhonda Patrick.

• Link to full study.