Time in Nature and Stress: How Much Is Enough?

Many people feel calmer after a walk in the park, and researchers have started to measure why. A few well-designed studies have looked at stress hormones and at the mental habit of replaying worries. This guide explains what they found, how much time seems to be enough, and easy ways to fit it into a busy week. It is general education, not medical advice or therapy.

A walk and a quieter mind

In 2015, a Stanford team led by Gregory Bratman published an experiment in the Proceedings of the National Academy of Sciences. Thirty-eight city residents were randomly assigned to take a 90-minute walk, either in a natural setting with grass and trees, or along a busy urban road.

• The nature walkers reported less rumination. Rumination is the repetitive, self-focused worrying that can feed low mood.
• Brain scans showed less activity in a region tied to rumination (the subgenual prefrontal cortex) after the nature walk.
• The urban walkers did not show these changes.

How much time is enough?

In 2019, Mary Carol Hunter and colleagues at the University of Michigan published a study in Frontiers in Psychology. Thirty-six urban adults were asked to spend at least 10 minutes outdoors in a place that gave them a sense of contact with nature, three or more times a week for eight weeks, and to give saliva samples before and after.

• Stress hormone fell. Cortisol dropped more after a nature break than would be expected from its normal daily decline.
• Twenty to thirty minutes gave the most benefit for the time spent. Longer visits kept helping, at a slower rate.
• The activity did not matter much. Sitting, walking or other quiet activities all worked.

Keep the limits in mind

• The studies were small. Dozens of people, mostly adults living in cities.
• Participants chose their own places and times in the second study, so it describes patterns, not cause and effect.
• The 20-minute number is a guide. It is an estimate from one study and not a medical prescription.
• Nature is not a treatment. It is a helpful habit, but it is not a substitute for care if you are struggling.

Easy ways to try it

• Use what is nearby. A park, tree-lined street, garden or riverbank counts.
• Take a phone-free lap. Leave the headphones for part of it and notice sounds, light and air.
• Pair it with walking. Our guide to how much walking is enough has ideas.
• Take your lunch outside. Even a bench works.
• Bring a friend. Time outdoors with someone is a nice way to catch up.
• Add a calming pause. Try some of the breathing exercises while you sit.

Why it fits with eating and weight

Stress is a common trigger for eating when we are not hungry. Our guide to stress eating explains how, and a regular outdoor break can be one gentle way to give stress a different outlet.

In short

Time among trees and open sky seems to quiet the mind and ease the body’s stress response, and it does not take hours. A short, regular visit to a green spot is a simple habit that costs nothing and is easy to start today.

Sources

• Bratman GN, Hamilton JP, Hahn KS, Daily GC, Gross JJ. Nature experience reduces rumination and subgenual prefrontal cortex activation. Proceedings of the National Academy of Sciences, 2015;112(28):8567-8572.
• Hunter MR, Gillespie BW, Chen SY-P. Urban nature experiences reduce stress in the context of daily life based on salivary biomarkers. Frontiers in Psychology, 2019;10:722.