Cold water swimming: a healthy habit

Dipping and swimming in cold water is increasingly being touted as good for health. But what does the science say? By Elaine K Howley

For roughly seven years, the young woman named Sarah who was described in a 2018 case study published in the British Medical Journal had struggled with major depressive disorder. She was diagnosed at age 17 – though she’d been experiencing symptoms long before that – and by the time she was 24, she had tried various different anti-depressant drugs. These largely failed to control her condition and left her with unwanted side effects.

At age 24, Sarah gave birth to a daughter and decided she wanted to live both depression- and medication-free. This would be a tall order, but not insurmountable, as the case study describes, because Sarah had access to a secret weapon many of us swimmers already know about: cold water.

Under the guidance and observation of a team of cold-water researchers at the University of Portsmouth, Sarah began undertaking weekly swims in open water in April, and immediately noticed an improvement in her mood after each swim. That boost in spirit lingered long after Sarah had warmed up. Over the course of the six-month study period, Sarah continued her once-weekly sea swims, increasing her time in the water to about half an hour by the conclusion of the study in September.

Though this is just one person’s experience, the result offers some compelling evidence that cold water has the power to cure what ails you; in Sarah’s case, within four months of beginning a cold-water swimming regimen, she no longer needed any medication to control her depression.

Is cold water the key to good health?

Sarah’s story – like those of so many other people who’ve stumbled into open water swimming as a means of managing stress, improving their mood, or just for fun – illustrates that there could be several potential medical applications for cold water therapy. While the most prominent and so-far best explored area relates to mental health conditions such as depression and anxiety, researchers have been investigating how other aspects of health may improve with cold water swimming including:

• Type 2 diabetes
• Migraine
• Arthritis
• High blood pressure
• Multiple sclerosis
• Inflammatory bowel disease
• Fibromyalgia
• Post-traumatic stress disorder
• Pain
• Long COVID

That’s a lengthy list of some of the most vexing of chronic health conditions experienced by billions of people worldwide. A vast pharmacological industry aims to address and treat these conditions with a host of powerful chemicals and medications. But might it be that a discipline of cold-water immersion could be a simple solution for all of it? And if so, why?

Science doesn’t have a firm answer to those questions just yet, all the experts note, because what evidence does exist is largely anecdotal. More comprehensive, scientific studies will be needed before we can say for certain exactly how cold water affects health and how to get the most from a cold water swimming habit. But the effects appear to be grounded in how your body responds to the stress of getting cold.

How cold water affects your body

Currently, most scientists investigating this subject have noted that cold water appears to quell inflammation, which is a common component of all of the above listed chronic conditions.

Inflammation is a central part of the immune system – the body’s innate defence mechanism that leaps into action when you’re exposed to a pathogen or sustain a trauma or injury.

In appropriate doses, inflammation is a good thing – it’s how the body heals itself. But in large, chronic doses, such as can be induced while living a modern, stressful life with perhaps a poor diet, inadequate sleep, and so on, inflammation levels can climb. It’s just your immune system trying to take care of business, but over time, chronically high inflammation levels can turn into conditions like heart disease, obesity, and type 2 diabetes.

However, regular immersion in cold water appears to mitigate those elevated inflammation levels. And it makes sense – for decades, doctors have recommended applying ice to bring down the redness and swelling that occurs after you’ve sustained an injury. It seems that dipping your whole body into cold water could have a similar impact across the whole system to reduce inflammation.

The exact inflammatory mechanism and how it’s derailed by cold water is still being explored, but it appears the be related to how the body adapts to training stimuli. The body craves stability and equilibrium, and your whole system is finely attuned to keep your body humming along within a set zone.

But when a stressor is applied, that can tip the body out of its preferred low-maintenance range and it forces the body to work harder. Whether that stress is related to temperature, increased physical demands, or any of a vast constellation of factors, the body’s stress response ramps up.

When such stressors are routinely and deliberately applied, they can nudge the body in a specific direction that you’d like it to go. This is the theory behind how any kind of physical training works, and it seems the same holds true for cold adaptation.

There are also powerful innate systems at work when you enter cold water, namely the sympathetic nervous system and the parasympathetic nervous system. These two systems have opposing roles in the body. The sympathetic nervous system is the so-called fight-or-flight response that’s triggered when you’re put in a stressful situation.

The parasympathetic nervous system, on the other hand, is known as the rest-and-digest system. It carries signals throughout the body to help you relax and recover. The two systems work side-by-side to keep your body in that balanced zone it loves so much.

However, exposure to cold water can trigger both systems; when you submerge your body in cold water, that triggers the sympathetic nervous system, as the body assumes you’ve fallen in by accident and you need to ramp up your muscles and stress hormones to get yourself out of danger; think fight AND flight until you can get back to warmer ground.

But when you submerge your face in cold water, that triggers the parasympathetic nervous system. This is why splashing cold water on your face after you’ve gotten upsetting news can help you calm down. It’s the same, ancient response system that helps seals slow their heart rate and hold their breath when diving under water in search of food.

These two complex response systems can clash when you enter cold water, so it’s best to approach it slowly. But both responses can have powerful, long lasting effects on your overall health and wellbeing.

Future studies

Given the body’s complex response to immersion in cold water, it’s no wonder dipping and swimming could be more than just a means of keeping fit.

Currently, the most compelling evidence for the clinical application of cold-water swimming as a therapeutic approach relates to mental health, as a variety of cold-water swimming groups that have sprung up recently around the UK are finding.

So far, it’s not entirely clear exactly how much benefit practitioners derive from the cold water itself versus other factors that come into play alongside it in such settings, such as being more physically active and enjoying social engagement. Both being social and getting more exercise are strongly associated with improved overall health and lower levels of systemic inflammation. But it seems the cold itself really does add a little something to the mix for those who partake regularly.

How cold the water needs to be, how frequently a patient would need to engage in swimming, and how long each session must last to derive a benefit are three large questions that remain unanswered, but during a video presentation for How To Academy Science, Dr Mark Harper, author of Chill: The Cold Water Swim Cure – A Transformative Guide to Renew Your Body and Mind, said that there’s no need to overdo it – a few minutes is usually enough.

“Measurable benefits have been noted in water that’s just less than 20 degrees Celsius, so you don’t have to be Wim Hof, just go for a swim in the sea in the summer. It’s not about suffering. It’s meant to be fun.”

He adds that “becoming hypothermic is always bad for you,” so it’s best to exit the water before you get into trouble.

While we wait for stronger evidence, it’s worth underscoring that each anecdote of someone getting relief from cold water swimming provides additional support for its use in clinical settings.

So, for the time being, there’s no reason not to give cold-water swimming a try. Find a group and get moving. Even if you don’t see a massive shift in your overall health, you’ll probably have a good time regardless. And the cake afterwards makes it all worthwhile.

What qualifies as cold?

Naturally, there’s a lot of variability in what each person thinks is cold water; I swim with several folks who reach for the wetsuit when the water hits 20 degrees Celsius, but some other friends of mine are happy to keep going without any thermal protection until the water becomes solid ice.

Divining a definitive temperature point at which benefits can be derived from immersion isn’t completely straight forward, and there’s not always consensus among swimmers about what constitutes cold water. But the RNLI and the RLSS use the following scale to define what they consider cold water swimming:

• Below 15 degrees = cold water
• Below 10 degrees = very cold water
• Below 5 degrees = ice swimming.

Read more our guide to cold water temperature.

Dr Harper’s six rules for a safe and enjoyable cold water swim

During a video presentation for How To Academy Science, Dr Mark Harper shared the six cardinal rules of staying safe while enjoying a cold water swim.

Rule 1: Before getting in, know how you’re getting out. It’s always easier to get yourself into something than to get out, so make a plan for exiting the water well before you even start your swim. Make a plan and swim your plan.

Rule 2: Warm up before you get in. Get as much heat stored up in your system as possible to delay the onset of hypothermia.

Rule 3: Get your body in before your head. If you dive head-first into cold water, that increases your risk of triggering a cardiac event because of the potential for autonomic conflict – that’s when the sympathetic and parasympathetic nervous systems have both been triggered and are working against each other. Avoid this by slowly walking into the water and giving your body time to adjust before putting your face in.

Rule 4: Focus on your breathing. Calm your breathing and relax into the cold.

Rules 5: Be smart when you get out. When you get out of the water, move quickly to get out of the wind, get dry, get warm. Afterdrop – the continued cooling of the body after you’ve left the water – is real, and it happens because you’re no longer generating heat in the muscles from exercise. It can overtake you quickly, so take rewarming seriously. The less you continue cooling after you’ve stopped swimming, the better.

Rule 6: Always swim with a friend. Cold water swimming is always better together, so find a group and help keep each other accountable.

Click here for more guidance on cold-water swimming