The Science behind OUTSIDE2

Spnt.OUTSIDE@nhs.net

Why are we doing a study and what has been done already?

Many people –including some of the team – have found outdoor swimming beneficial for their mental wellbeing. From the basic science, from anecdotal evidence, from the studies we have already undertaken and from our own experiences, we think there is strong basis for thinking that outdoor swimming could be used as a treatment for the symptoms of depression.

The aim of this study is to provide high-quality evidence to see if outdoor swimming is helpful and cost-effective for people experiencing depression.

The idea that cold water swimming could be used therapeutically was supported by research showing that the body’s reaction to stress becomes less intense after repeated immersion in water under 20˚C. As a result, when Professor Mike Tipton MBE, head of the Extreme Environments lab in Portsmouth, was asked by doctor and TV presenter, Chris van Tullekan, about how they might use cold water swimming in his upcoming programme ‘The Doctor who Gave Up Drugs’, he suggested investigating depression.

One brave woman, Sarah, [link to video] volunteered and over the next few months, she found she was able to manage her mental health by swimming outdoors, substituting the activity for the tablets she was taking.

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Technical Summary

Swimming Survey Video by Millstream Productions

Around this time, members of the OUTSIDE research team started to explore whether and how outdoor swimming was impacting on mood amongst people who were choosing to swim outside. A study of people undertaking an introductory course in sea swimming showed that, compared to people who just watched from the shore, their wellbeing and mood improved. [link] In addition, qualitative research exploring the experience of regular sea swimmers indicated that the activity positively impacted on their wellbeing. [link]

The next step was to investigate the impact of outdoor swimming on people who were struggling with symptoms of anxiety and depression. A single armed trial (single because it only has an intervention group) was undertaken to see if it was possible to recruit people with anxiety and depression to an outdoor swimming course and whether it had the potential to be effective. Fifty-three people completed the swim course; their feedback, and the changes in mood that they reported, was sufficiently positive to justify investigating this potential intervention further. [link]

Without a control group – a group who are part of the trial but do undertake the intervention during the study – it is impossible to know how much (if any) of the effect can be attributed to the swim course. The next stage was, therefore, to run a small study (OUTSIDE 1), to see if it was possible to undertake a randomised controlled trial [link].

Undertaking this small study had a number of purposes; one was to determine if it was possible to recruit participants, another was to determine if the design can be improved through gathering feedback from participants and stakeholders, and finally to quantify any changes in mental health as a result of the course by comparing the intervention and control groups. From these figures it was then possible to work out the number of participants required for this current, large-scale study that will be able to provide a statistically robust answer as to whether or not cold-water swimming is an effective intervention for depression.

Science – Technical Summary

There is growing evidence that access to the natural environment (green and blue spaces) is linked to improving mental health1,2. Green exercise initiatives show great promise in improving wellbeing. MIND commissioned an evaluation of 25 ecotherapy projects, in which participants were encouraged to be active outdoors, and found measurable improvements with 7 out of 10 people experiencing significant increases in wellbeing, social inclusion, healthier lifestyles, greater connection with the natural world and adoption of environmentally-informed behaviours3. However, not all types of green and blue exercise will equally engage all people, for instance, due to injury or poor motivation to do the activity. Therefore, a range of nature-based activities are required so that people can find and choose a preferred activity with which they can best engage.

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Much blue space research has focused on being alongside water. The popularity of open water swimming is growing4 and many are reporting transformative experiences and a greater connection to nature7 as well as benefits to their mental health5-8. The qualitative evidence available so far provides a foundation for the development of further research and indicates that nature-based activity within water offers additional benefits over and above that of exercise alone that could contribute to improved mental health and wellbeing. These include being “present”9, a sense of escape from everyday life10 and developing resilience11 as a risky activity becomes an enabling one12. The experience of activity in water has been described as “transformative, connecting and reorientating” as participants enjoy feeling better after a swim, a sense of connection to nature and others and developing different perspectives about themselves and the world7. There are also a range of possible physiological mechanisms as a result of activity in water that may contribute to an impact on mental health (e.g. cold water vagus nerve stimulation12,13, “post swim” stress hormone responses14, cross-adaptation and reduced cortisol responses14,15 and reductions in inflammatory responses16).

We have also started to show with our previous research, including a case study17 a survey8, and exploratory studies18,19, that swimming outdoors may be associated with improvements in wellbeing and reductions in symptoms of depression and anxiety. We undertook an observational study using an outdoor swimming programme, and found improvements in mood and wellbeing in a healthy sample with no declared mental health issues18. From a single arm study19, we recruited 53 participants with a range of depression severity levels to participate in an outdoor swimming course (8 sessions). Following the course there was a mean reduction in Patient Health Questionnaire-9 (PHQ- 9) scores of 7.8 points. 80.6% ‘recovered’ and 62.3% showed ‘reliable improvement’ (based on Improving Access to Psychological Therapies Guidance)20.

Further trials using robust designs, including randomised control trials (RCTs) incorporating mixed methods, are required according to a recent report to DEFRA21 to understand if nature-based activities such as outdoor swimming potential has to support recovery in people living with symptoms of depression.  As outdoor swimming can also be hazardous12, well-planned empirical research is needed to determine if it is safe and as helpful as early research suggests, before recommending it as an evidence-based treatment for depression. Likewise, it is essential to determine whether sufficient numbers of people with depression will be interested in participating in the intervention, who it most benefits and if it is less attractive to some members of the population and whether measures can be put in place to address this.

Our previous trial, a feasibility RCT22 (OUTSIDE 1), provided evidence of the potential to recruit and retain as well as the safety record for conducting such an RCT. Although the study was not statistically powered to detect between-group differences, it showed a strong signal for positive outcomes with between-group differences in reductions in symptoms of depression and anxiety in the outdoor swimming group (intervention arm) compared with the control group.  The health economic evaluation showed that the percentage of participants reporting use of depression-specific therapy was lower in the intervention than in the control arm post-treatment and at follow-up. In addition, the use of antidepressants and sleeping tablets, on average, reduced more in the intervention than in the control arm for the trial duration. These promising findings provide a platform for a full-scale RCT to examine the clinical and cost-effectiveness of the swim course intervention. If trial hypotheses are supported, the intervention could be scaled up nationally to provide the intervention across the UK.

  1. https://www.cambridge.org/core/journals/bjpsych-international/article/importance-of-greenspace-for-mental-health/EEFD7077B5E3823086FB187FABE535C2 
  2. https://www.who.int/europe/publications/i/item/9789289055581 [Accessed July 7, 2022]  
  3. https://www.basw.co.uk/resources/feel-better-outside-feel-better-inside-ecotherapy-mental-wellbeing-resilience-and-recovery [Accessed July 7, 2022]
  4. https://outdoorswimmer.com/wp-content/uploads/2022/04/TrendsReport_Full_LR.pdf
  5. https://doi.org/10.1002/lim2.12
  6. https://www.sciencedirect.com/science/article/abs/pii/S1755296622000345#! 
  7. https://www.tandfonline.com/doi/abs/10.1080/2159676X.2019.1649714
  8. https://www.i-jmr.org/2022/1/e25589
  9. https://doi.org/10.3390/su14106364
  10. https://doi.org/10.1080/2159676X.2020.1761433
  11. https://doi.org/10.1177/0193723520928597
  12. https://physoc.onlinelibrary.wiley.com/doi/10.1113/EP086283
  13. https://doi.org/10.1113/JP271539
  14. https://doi.org/10.1016/0091-3057(85)90083-8
  15. https://doi.org/10.1113/jphysiol.2010.193458
  16. https://doi.org/10.1080/00365510701516350
  17. http://dx.doi.org/10.1136/bcr-2018-225007
  18. https://onlinelibrary.wiley.com/doi/10.1002/lim2.12
  19. https://www.sciencedirect.com/science/article/abs/pii/S1755296622000345?via%3Dihub
  20. https://www.england.nhs.uk/wp-content/uploads/2020/05/iaptmanual- v4.pdf Accessed May 26
  21. https://arcswp.nihr.ac.uk/wp/wp-content/uploads/2021/06/15138_TherapeuticNature-Finalreport.pdf [Accessed May 14, 2023]
  22. https://pilotfeasibilitystudies.biomedcentral.com/articles/10.1186/s40814-023-01358-3
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