Study to explore if outdoor swimming is helpful for depression after successful trial

28 March 2024

Researchers looking into the effectiveness of outdoor swimming to help people reduce symptoms of depression, say the trial results are “promising” as they begin the next stage.

Sussex Partnership NHS Foundation Trust joined forces with the University of Portsmouth to carry out a feasibility trial last year involving 87 people with mental health difficulties. The first part of this project was to see if people would sign up to take part, and also whether they remain engaged in the study to the end. 

Outdoor swimming has been hailed over the past few years as a way to improve health and wellbeing, but this is the first official clinical trial to explore the benefits of the activity in adults with depression. 

They are now recruiting more participants to take part in a larger randomised control trial (RCT) at 15 sites in England, to determine if those with mild to moderate depression benefit from an outdoor swimming course and explore reasons why any changes occur.

The two-year and a half year study, called OUTSIDE, has been funded by the National Institute for Health and Care Research (NIHR). It will involve 480 adults with symptoms of depression. Some participants will be given an 8-session outdoor swimming course in addition to usual care, and then compared to a control group who are receiving their usual care. 

Researchers will explore whether the sessions lead to greater reductions in the severity of depressive symptoms and anxiety up to 38 weeks after the trial. They also want to see if it leads to greater improvements in mindfulness, and be a safe and cost-effective intervention to run.

Hannah Denton, Principal Counselling Psychologist at Sussex Partnership NHS Trust, added: “After many years and lots of hard work, it is really exciting that this project is finally happening! It will be interesting to find out more about how outdoor swimming can impact on mental health, and if we find it is beneficial, then hopefully this research will result in more opportunities for people to take part.”

Before the pandemic, the number of adults experiencing moderate to severe depression in the UK was 1 in 10, but this doubled, to nearly 1 in 5 between March and June 2020.

There is emerging evidence to suggest that regular open water bathing could have a positive impact on a person’s mental health. Immersion in cold water is believed to reduce stress levels and generates a greater sense of wellbeing.

Clara Strauss, Deputy Director of Research at Sussex Partnership and Professor of Clinical Psychology in the University of Sussex School of Psychology, said:  "This is the first large trial of its kind that will tell us if outdoor swimming is helpful for people living with depression. If it is, this could increase the range of options available to people as they find their path to recovery."

Previous research by the University of Portsmouth team and their collaborators found swimming outdoors may be associated with improvements in wellbeing. An observational study in 2020 found improvements in mood in a healthy sample with no declared mental health issues. 

In a separate study in 2022, 53 participants with a range of depression severity levels, participated in an outdoor swimming course (8 sessions) on the North Devon coast. A post-study questionnaire found 81 per cent of participants felt 'recovered', and 62 per cent showed 'reliable improvement' to their mental wellbeing.

Swimming sessions will take place at locations across the country. They will include a mix of sea swimming, lakes, and semi-heated outdoor pools. Each course can facilitate up to 10 people, so the team will operate on a first come first serve basis. 

The study will begin in the summer months, when the water is warmer. Participants will be medically screened before being accepted to take part, and a team of medics will be on hand throughout the study to ensure their safety.