# Five outpatients with depression kept swimming in cold water twice a week, their wellbeing score rose from 39.2 to 54.0 and sleep scores improved, yet the 13-person feasibility study was built to test safety and participation before anyone could claim a proven treatment effect

> Five patients with depression kept showing up for cold water swimming twice a week and by the end of a small Danish feasibility study their average well-being score had climbed from 39.2 to 54.0 while their sleep score also moved in a...

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Byline: ARGO.net Editorial Team
Published: 2026-08-13T11:35:02+00:00
Categories: Explainer, Health

![Cold water swimmers entering an icy lake](https://www.argo.net/wp-content/uploads/2026/08/cold_water_swimmers_entering_an_icy_lake.jpg)

Five patients with depression kept showing up for **cold water swimming** twice a week and by the end of a small Danish feasibility study their average well-being score had climbed from 39.2 to 54.0 while their sleep score also moved in a better direction. The paper, indexed by [PubMed](https://pubmed.ncbi.nlm.nih.gov/37381680/), describes a supervised add-on program rather than a replacement for standard care and it reports a result that is easy to overread if the study's design is left out.

The important design detail comes first: this was an **open-label feasibility study** involving 13 recruited outpatients, with only five participating on a regular basis. Feasibility studies ask whether a program can be carried out safely and consistently. They do not establish the kind of causal evidence that would come from a larger randomized trial with a control group.

Depression research has to keep established care in view because the illness is common, serious and treatable through established forms of care, as the [World Health Organization](https://www.who.int/news-room/fact-sheets/detail/depression) notes. A supervised dip in winter water may end up helping some patients, but the current paper only supports a narrower claim: the researchers found that regular, monitored participation appeared possible and safe in a very small selected group.

## What the researchers actually tested

The study, published in [Nordic Journal of Psychiatry](https://doi.org/10.1080/08039488.2023.2228290), asked a practical question before a clinical one. Could adults already diagnosed with depression join a structured cold water swimming program without obvious safety problems and would enough of them keep participating for a larger trial to make sense?

All patients aged 20 to 69 years from an outpatient clinic were eligible for inclusion. The intervention was simple in outline: **twice-weekly, group-based swimming** in cold natural water during winter. Before participation, patients went through a somatic evaluation to make sure they were physically fit for the exposure.

The abstract does not describe a randomized comparison group, blinding, or a design that could separate the water exposure from other influences such as expectation, group support, seasonal changes or ongoing treatment. Researchers who start with a feasibility design are trying to learn whether the procedure can be delivered at all and whether the next study should be larger and more controlled.

The phrase **add-on treatment** also sets the boundaries of the test. Patients were not asked to abandon regular depression care and try winter swimming on its own. The intervention was layered on top of existing treatment, which makes the study more realistic from a clinical point of view, while also making it harder to isolate which part of the overall care experience produced any improvement. The [National Institute of Mental Health](https://www.nimh.nih.gov/health/publications/depression) describes depression treatment as a process that commonly involves psychotherapy, medication, or both, which helps explain why the paper treated swimming as an addition rather than a substitute.

## Why only five regular swimmers matter so much

The outcome scores that attract the most attention came from **five patients who participated on a regular basis**. Thirteen patients were recruited, yet only those five kept joining the sessions consistently. A group that small can swing sharply when even one person's experience is unusually positive or unusually difficult.

Small samples create two problems at once. They make the result unstable and they make it harder to know who the result applies to. A person willing to keep entering cold water through winter may differ from other patients in motivation, physical tolerance, schedule flexibility or symptom pattern and those differences can influence both completion and outcome.

Feasibility work often lives with those limits because its first goal is operational. The present paper therefore says less about how well cold water swimming treats depression than about how difficult it may be to recruit, screen and retain participants for a demanding intervention that many people will understandably decline.

Adherence is part of the result here, not just a side note. A treatment that looks promising among the people most willing to continue may still have limited real-world usefulness if many eligible patients do not start, stop early, or find the routine too burdensome. The abstract does not spell out each reason for irregular participation. Even so, the gap between 13 recruited patients and five regular swimmers signals that any future trial needs to treat retention as a central outcome.

## The reported changes in wellbeing and sleep

Among the regular participants, the reported **well-being score** rose from 39.2 at baseline to 54.0 at the end of the study. The team also tracked sleep with the [Pittsburgh Sleep Quality Index](https://pubmed.ncbi.nlm.nih.gov/2748771/), a widely used questionnaire for sleep quality and disturbances over the previous month. In that measure, lower scores generally indicate better sleep.

The participants' average PSQI score was 10.4 at baseline and 8.0 at the end. That shift suggests better sleep and the abstract's conclusion reflects that possibility. The wording stayed cautious: regular participation **may improve sleep and well-being**. For a study this small, that single verb carries much of the scientific honesty.

Those two outcome measures also capture different parts of daily life. A well-being score can reflect mood, energy and general functioning, while the PSQI is aimed specifically at perceived sleep quality and related disturbances over the prior month. Seeing both move in a favorable direction makes the pilot more interesting, but it still does not remove the possibility that the same people who managed to keep attending were also the most likely to report improvement over time.

Measured change alone does not reveal the mechanism behind it. The cold exposure itself may have contributed. The group format, the routine of meeting twice a week, the expectation of benefit, continued standard treatment, exercise, or the satisfaction of completing a difficult task could also have played a role. The study was not built to separate those explanations.

## What safety means in a study like this

The paper's clearest positive finding is about safety and participation under supervision. Several patients had **somatic comorbidities**, yet all who entered the intervention passed the physical evaluation and were considered fit to take part. Within the limits of the abstract, the study did not report a safety signal strong enough to stop the program.

Cold water swimming can still place real stress on the body. Sudden immersion triggers **rapid breathing**, blood vessel constriction and a rise in cardiovascular strain, which is why screening and supervision matter. A structured trial with medical oversight is very different from treating icy water as a casual home remedy.

The study also framed cold water swimming as an **add-on treatment**. That wording is essential. The program sat beside regular care rather than replacing psychotherapy, medication or other evidence-based treatment plans. Readers looking for a simple alternative should keep the article's actual scope firmly in view.

## What a stronger next study would need to show

A larger follow-up trial would need a design that can answer the clinical question left open here. Researchers would want more participants, clearer reporting on who dropped out and why and a comparison group that receives usual care or another structured activity. Those steps would make it easier to test whether the water itself adds something beyond exercise and social contact.

Future work would also need to measure benefit over a longer period and examine who responds best. Depression is not one uniform condition and people vary in severity, comorbid health issues, treatment history and willingness to keep doing a challenging activity. A sample of five regular swimmers cannot define any of those patterns and it cannot show whether the reported gains would hold up after winter ended or after enthusiasm from joining a novel program faded.

A stronger controlled trial would also need to specify what counts as success before the data are collected. Researchers could compare symptom scales, sleep measures, attendance, adverse events and treatment continuation across groups. They would also need enough participants to tell whether any apparent gain is larger than the normal week-to-week variation that often appears in depression and sleep questionnaires.

For now, the study offers a careful pilot result rather than a breakthrough. It suggests that **supervised cold water swimming** can be explored in selected patients with depression and it leaves the larger therapeutic claim exactly where responsible researchers should leave it: open, interesting and still unproven.