It’s 8am, and I find myself at the edge of my local lake in Beckenham Place Park, London, with the early morning sun just starting to break through the trees. A veil of mist rises from the chilled waters, wrapping everything in silence. Even the ducks seem to shy away from the frigid water today. Yet, my friend and I, clad in swimsuits despite the single-digit water temperature, brace ourselves. The initial plunge is startling, but once you acclimate and begin gliding through the water, it feels like a rebirth.

In recent years, I’ve successfully turned numerous friends into proponents of cold water swimming. My mantra is straightforward: nothing boosts mental health more effectively. Until recently, my experience was mostly just personal testimony. However, with the rise of ice baths, cold showers, and winter swimming, researchers are starting to uncover how these frosty immersions influence our brain chemistry. It’s becoming clear that these weekly dips may be making lasting changes to my brain.

I’m certainly not alone in my fondness for cold water. 6.8 million individuals in the UK regularly swim outdoors, whether in open waters or chilly pools that remain cool throughout much of the year. This trend aligns with emerging evidence indicating that consistent cold water exposure can alleviate fatigue, decrease depression symptoms, and enhance overall well-being, despite its potential dangers like hypothermia and waterborne illnesses.

For instance, a study involving 36 participants who undertook a four-month open water swimming program, four days a week during winter, demonstrated a marked reduction in tension and fatigue when compared to a non-swimming control group that maintained typical city life. The swimmers reported heightened energy levels, better memory retention, and improved mood.

A recent single immersion also proved effective. Individuals who stood chest-deep in seawater at around 13.6 degrees Celsius (56.5 degrees Fahrenheit) for 20 minutes reported less negativity and an increase in energy and self-esteem relative to those who remained on the shoreline.

Cold exposure affects several physiological mechanisms, including the heart and immune system, often leading to enhanced immune function which reduces the incidence of colds and cardiovascular risks. What intrigues me most are the neurological impacts.

For example, immersing your half-clad body in frigid water can uplift your mood by triggering an acute stress response. Anyone who has leapt into icy waters knows this feeling. The brain manages the sudden release of adrenaline, dopamine, and cortisol—chemicals that induce a high similar to that experienced post-exercise.

This reaction serves as an evolutionary survival tactic. Exposure to extreme cold can be life-threatening, which is why this “cold shock response” harnesses stress mechanisms to offer bursts of energy, sharpen alertness, minimize pain, and avert danger.

This is also the reason swimming in cold water might be overwhelming. In unusual cases, it can provoke rapid breathing and could lead to cardiac incidents if not approached with caution. However, if you intentionally prompt this reaction in a safe, calm setting with trained supervision, the benefits can be enjoyed while minimizing risks. Deficiencies in these neurotransmitters are critical in conditions like depression and anxiety, making the artificial elevation of these chemicals a possible explanation for the fleeting mood boost many experience after swimming.

There may also be long-term benefits. Over time, the body adapts to the stress of cold water immersion, leading to shifts in the stress response. A study found that participants swimming in cold water three times a week for 12 weeks experienced a reduction in cortisol levels by the end, indicating an enhanced ability to cope with stress. Chronically high stress hormones can lead to inflammation, linked to various diseases and accelerated aging; thus, managing this response may yield long-term health advantages. A recent review of cold water swimming research suggests that this adaptation could provide expansive mental health benefits, like aiding anxiety management.

Additionally, our cold shock response triggers the release of proteins, such as RNA-binding motif 3, which assist in synaptic repair (the links between neurons). In lab mice prone to a form of Alzheimer’s, increased levels of this protein have been found to shield against nerve damage. This has led some researchers to propose that regular cold water swimming could provide lasting neuroprotective effects in humans, although this remains unverified.

Cold water immersion also wields significant psychological power. Enduring challenging conditions—even the most avid cold water enthusiasts can face trials during icy days—can foster resilience and a sense of mastery, popularly referred to as grit. Coupled with the social elements inherent in outdoor swimming, this mirrors some aspects of treatments like antidepressants and therapy. In fact, emerging evidence indicates that cold water swimming can alleviate depression symptoms as a complementary treatment. In many instances, this can occur without reliance on medication.

Interestingly, researchers are beginning direct investigations into cold water swimming’s effects on the brain. For example, Alla Yankovskaya and her team at Bournemouth University recently scanned the brains of 33 individuals not accustomed to cold water swimming before and after a five-minute full-body immersion in water at 20°C (68°F). This marked the first time researchers obtained real-time data on the interplay of brain networks post-cold exposure.

They uncovered advantageous changes in connectivity between various crucial brain regions, particularly linking the medial prefrontal cortex and the parietal cortex, areas tied to emotional regulation, focus, and decision-making. Activity in these regions is often disrupted in individuals suffering from depression and anxiety, possibly underscoring why cold water swimming acts as a therapeutic modality.

However, not everything is clear cut and positive. In rare instances, temporary memory loss may arise from cold water swimming, typically observed in older individuals, although the cause remains elusive. Besides, hypothermia poses a risk for lengthy aquatic adventures. Nevertheless, it’s comforting to know that the mental clarity and elevated mood observed after a swim are substantiated by scientific evidence, and maintaining such benefits might even guard against age-related diseases.

Recently, I learned that a sauna was being constructed lakeside, prompting curiosity about the additional benefits heat therapy might offer alongside swimming. I came across studies suggesting heat and cold can induce precise alterations in brain wave patterns, potentially yielding the most significant cognitive benefits of all. This is certainly a topic I aim to delve into in future articles—all in the name of science, of course, as I embark on a personal investigation of the UK’s premier saunas.

In the meantime, if you find yourself near a lake or the ocean this winter, gather your courage and dip your toes in. It may be chilly, but your brain will appreciate it.

Swimming in waters below 15°C (59°F) should always be conducted with a partner, flotation device, bright headwear, and full awareness of the risks involved and how to mitigate them. For more information on water safety pertaining to cold water swimming, visit the Royal Lifeboat Society. Resources are available.