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Twenty minutes’ contact with nature is all it takes to reduce stress hormone levels

Photographie d'une balade dans la nature

That was the finding of a recent study (1) conducted by researchers at the University of Michigan. Communing with nature for just 20-30 minutes is sufficient to reduce levels of cortisol, known as the ‘stress hormone’.

Cortisol, the hormone at the heart of the stress mechanism

A stressful situation places energy demands on the body, leading to an imbalance. The adrenal glands, which sit on top of the kidneys, respond by secreting the famous cortisol, a hormone which triggers the mobilisation of sugar reserves, regulates their use in the body, and activates glycogen synthesis primarily in the liver.

For the body then, the energy required for the response to stress is actually represented by sugar! Directly measuring the level of cortisol in saliva provides a reliable snapshot of an individual’s state of stress.

Participants asked to conduct their own experiment with nature

Over an 8-week period, individuals participating in the University of Michigan study were asked to spend a minimum of 10 minutes in nature, at least 3 times a week. They were free to choose the form this took – sitting, walking or a combination of the two - but it had to be somewhere outside with enough natural elements to make them feel they were interacting with nature. This flexibility enabled the researchers to estimate stress levels in a way that fitted into people’s busy and often unpredictable schedules.

A few constraints were imposed in order to make the experiments more uniform and to minimise factors likely to influence participants’ stress levels: no internet, no social media, no telephone calls, no conversations and no reading.

Reduced cortisol levels following time spent in nature

The results were clear: 20 minutes spent in nature was sufficient to reduce cortisol levels in saliva. If the period was extended to 20-30 minutes, cortisol decreased at its maximum rate. Over 30 minutes, and the level continued to fall but more slowly. The results were the same whether the participants were sitting down or moving.

These findings provide valuable information on the effects of time spent in nature and on the positive characteristics of this ‘green’ experiment. Spending time in this way can be considered an effective (and free!) treatment for managing stress, not only for those who live close to nature but also for urban dwellers who can benefit from natural spaces in a broader sense. Whether in the town or countryside, each of us can look to our environment to find our effective ‘nature pill’!

The study behind this article:

  1. MaryCarol R. Hunter, Brenda W. Gillespie, Sophie Yu-Pu Chen. Urban Nature Experiences Reduce Stress in the Context of Daily Life Based on Salivary Biomarkers. Frontiers in Psychology. Vol 10, n° 722. 2019.
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