The BBC’s Trust Me, I’m a Doctor looked at whether time spent in nature benefits mental health and ran a small experiment testing the recent finding, reported in one of Mat and co’s recent papers, that people who report spending 120 mins or more in nature over the last week had consistently higher levels of health and wellbeing than those who reported less or no time in nature.

You can watch the program on the BBC iplayer (you need a TV license to view the program): Trust Me, I’m a Doctor Series 9 Episode 4: Michael Mosley runs an experiment to test whether an extra hour a week in nature improves your physical and mental health.

Accompanying the program is a short article describing the experiment that the BBC carried out with one of our close collaborators Professor Catharine Ward-Thompson and Mat:

“We randomly assigned a group of 15 volunteers to one of two groups: the first would spend less than two hours a week in nature, the second would spend more than two hours. The aim was to test whether time in nature had a causal effect on wellbeing, stress and mood. We also wanted to find out if exposure to nature affected physiology– such as heart rate variability and cortisol levels, (cortisol is a hormone released under stress).

Our volunteers were all daytime workers, and spent their extra time in nature during their lunch break, in local nearby parks or green spaces. They were asked to sit, relax, or gently walk in nature, but not to walk briskly or do any vigorous exercise. Before and after contact with nature our volunteers filled out a questionnaire which assessed their mood – measures such as positive emotion, arousal, and stress.

At the beginning and end of our experiment, our participants filled out questionnaires which assessed their overall wellbeing [the WHO-5 Wellbeing Index] and their stress [the PSS Perceived Stress Scale].

In addition, their cortisol levels were measured in their saliva and their heart rate variability was measured using ECG electrodes applied to their wrists.

The results

At the end of the three weeks, the group experienced an overall reduction in perceived stress, and an overall increase in wellbeing.

Improvements were also seen in patterns of cortisol levels across the group, but these were very slight; a larger cohort may have yielded more significant results. We saw no indication of heart rate variability.

Comparing how people felt directly before and after nature exposure, our participants reported feeling more energised – increases in positive mood and arousal were found.

Remarkably and most importantly, the results of the experiment showed that those who spent 120 mins or more in nature per week saw a significant reduction in perceived stress levels of at least 30% – whereas those volunteers who spent less than 120 mins in nature per week did not see a significant drop in stress.

Perhaps surprisingly, weather did not make a difference. In the qualitative data, participants commented on the bad weather they experienced, in fact one participant even spent time in nature in a hail storm; however, this bad weather did not seem to affect the results they reported.”