The pros and cons of cold water immersion, and how to get started
Outside it was -13C. I was huddled as close as I could get to a wood burning stove in the centre of a canvas tent, carpeted by reindeer skins. I was wearing a swimming costume, with a dry robe draped around my shoulders.
“Next!” called Torgeir’s voice from outside, with a gentle Norwegian accent.
I was the last one. There was no getting out of it now. I ducked under the flap into the open air and my teeth started chattering in the biting wind. Out of my snow boots, my bare feet were sticking to the freezing ice. I tried to keep them moving, taking small, reluctant steps towards the ice hole.
Torgeir stood by a wooden ladder, which was leaning against one edge of a 1m by 1m square hole in the ice. The steps led down into dark pool of water, with chunks of ice floating on the surface. Torgeir tied a rope under my arms, in case I had to be pulled out.
I felt extremely nervous. The previous day, all 6 of my Norway adventure buddies had completed their first ice plunge. I had seen them shiver, and smile, and grimace and experience a rush of adrenaline on emerging back into the warming tent. I had stepped out to film them, but it was too cold to stay still and hold a camera for more than a minute or two and my fingers had frozen. I had refused the invitation to join them for a dip.
That evening, I had read up on the potential health benefits.. mood, heart health, immunity and metabolism, and perhaps even better sleep… So here I was; about to experience extreme cold water therapy for the first time…
What is cold water therapy?
Cold water therapy refers to the deliberate use of cold water for therapeutic benefit. This could be from a cold shower, via full immersion in a cold bath or ice bath, or swimming in cold or icy water.
There is no agreed definition of what counts as ‘cold water’ but the therapeutic response requires a cooling of surface tissues and core temperature, and a diversion of blood flow. Most of the research into cold water therapy uses temperatures which can be hazardous to health if exposure is unplanned and prolonged, which means 10 to 15 degrees Celsius, or 50 to 59 degrees Fahrenheit. Ice swimming takes place in water less than 5C.
Academic research investigating cold water exposure typically includes studies up to 20C, but even immersion in water <35C can cool the core body temperature if exposure continues for long enough.
What are the benefits of cold water immersion?
As I dipped my toes into the icy water, and stepped down the ladder, it seemed hard to believe that this experience could be good for me!
Much of the research evidence centres around short term benefits for pain relief and mood, but there is growing evidence of longer term benefits, especially for metabolism.
1. Analgesia: pain relief and reduction of muscle soreness
Cold water has been used to treat pain and to reduce swelling for thousands of years, with records suggesting that it was used in this way by ancient Chinese, Greek and Roman civilisations (Allan et al 2022). The cooling of tissues is thought to interfere with the conduction along pain fibres, reducing or numbing the sensation of pain.
Since the 1960s, ice baths have been used by athletes after intense training and competition to reduce muscle soreness and aid recovery. Cold immersion appears to reduce swelling and inflammation, and the perception of recovery. Being immersed in cold water also stimulates the release of leukocytes, white blood cells that help fight off sicknesses.
2. Focus, and concentration
Immersion in cold water acts as a physiological stressor on the body, pushing our autonomic nervous system into ‘fight or flight’ mode. The brain responds by triggering the release of the hormone noradrenaline, and to a lesser extent, adrenaline. In the immediate term these hormones make us feel energised, and can also make us feel agitated and eager to escape the water! Increases in these hormones can last for several hours, and can help some people to stay energised and focused.
3. Stress management and cardiovascular health
Although cold water acts as a stressor, one of the key benefits is thought to be the mind-body benefit of learning to embrace and deliberately tolerate that stressor. When we tell our conscious mind that we are choosing exposure to cold water, and we stay in, even when our stress response is activated, we start to exert top-down control over that stress response. This top down control can spill over into other areas, making us more resilient and better able to cope with other sources of stress. We are less likely to feel overwhelmed, and more likely to see difficult situations as achievable challenges.
There a physiological benefits to brief stressors too. The heart has to work harder on entry to cold water, but regular brief immersions with recovery give the cardiovascular system a chance to adapt – much like brief bouts of exercise. Cold adapted winter swimmers, or healthy people who start cold water acclimation for 5 weeks, tend to see improvement in markers of cardiovascular risk (Espeland et al 2022 ).
The stimulation of the stress response also promotes a slight increase in white blood cells, which can help us to fight off infection (Jansky et al 1996 ). However, one study study found no difference in the number of colds experienced by cold water or pool swimmers (Collier et al 2015).
Cold water immersion can also trigger the release of the feel good molecule, dopamine. Dopamine can enhance focus, attention, goal-directed behaviour – and make us keen to repeat our cold water immersion experience. Baseline dopamine levels can rise with repeated cold water exposure which may protect against depression, but more research on this link is needed.
Within moments of submersion in icy water, I did feel a strange sort of thrill – the buzz of the stress system kicking into action. But the real benefits for mood came later.. a huge sense of achievement of overcoming my fears, combined with the shivery jitters of my body working hard to bring my temperature back to normal.. and of course the relief that the experience was over.
5.Metabolism: insulin sensitivity and control of blood sugar
The body has to burn calories to increase core body temperature so cold water increases our basal metabolic rate. While the number of calories burned from the cold exposure is not that significant, cold exposure also triggers conversion of our normal white fat to a more metabolically active beige or brown fat.
Brown fat, or brown adipose tissue (BAT) is highly metabolically active. This means that over time people are able to be more comfortable in the cold and the more brown fat they have, the greater their ability to utilise glucose, and to control their blood sugar levels. Exposure to cold water or air boosts BAT's production of adiponectin, a protein that helps protect against insulin resistance, diabetes and other diseases. Cold-water immersions increase insulin sensitivity and decrease insulin concentrations for both inexperienced and experienced swimmers ( Espeland et al 2022 ).
Could cold water immersion help with sleep?
If you read articles by cold water swimming enthusiasts on the internet, there are claims that cold water immersion can help you fall asleep faster, and aid deep sleep. The section above explains why some of these benefits are plausible; improved control of the stress response, reduced pain and inflammation, and improved mood are all factors which could help with sleep quality. It could also be that cold water swimming, which is typically outside and often in the morning, has benefits for strengthening circadian rhythms with early light exposure and exercise.
However, to date (July 2022), I could not find any good quality published studies which have explicitly tested the effects of cold water immersion on sleep quality. This is definitely an area for further research!
I would suggest that from a sleep perspective, cold water immersion is not practiced directly before getting into bed. This is because it causes a stress response, which makes you feel more alert. Although there is a short term decrease in core temperature, which promotes deep sleep, the compensatory heating process triggered by shivering may in fact raise body temperature above baseline, and make it harder to fall asleep. For this reason, I’d recommend practicing in the morning. If the evening is better for you, wait at least an hour after fully recovering from cold water immersion before getting into bed, and if you notice any sleep difficulty, shift the immersion to earlier in the day.
What are the risks of cold water immersion?
If you build up your tolerance to cold water immersion gradually, and stick to dry land, it is possible to minimise the risks. However it is sensible to be aware of the risks: cold shock, nerve block, hypothermia and non-freezing cold injury (Tipton et al 2017).
Sudden immersion in cold water carries the risk of cold shock, and drowning – even in relatively little water. During the first 3 minutes of immersion some people experience gasping and hyperventilation (rapid breathing) as the brain kick starts the sympathetic nervous system, or stress response. If the face goes underwater, water up the nose can activate the dive reflex, which sparks the opposing parasympathetic nervous system. Activating both arms of the autonomic nervous system (para and sympathetic) can result in arrythmias or irregular heart beats, which can interfere with blood flow to the brain and heart. Individuals with heart problems should be particularly cautious about starting CWI.
After 3 to 30 minutes in cold water, there is a cooling of the nerves and muscles which can result in loss of muscular power. Nerve block, and temporary paralysis, may occur after exposure to a local temperature of between 5 and 15°C for 1–15 min in people who have not acclimatised to cold water.
Hypothermia becomes a risk after more than 30 minutes in cold water. The progressive signs and symptoms as core body temperatures lower are shivering (36°C), confusion, disorientation, (35°C), amnesia (34°C), cardiac arrhythmias (33°C), clouding of consciousness (33–30°C), loss of consciousness (30°C), ventricular fibrillation (28°C) and death (25°C) (Bierens et al. 2016).
Non-freezing cold injury
While not fatal, non-freezing cold injury is a condition similar to frostbite, where short immersions in very cold water, or prolonged exposure to cool water can cause severe pain, excessive sweating and cold sensitivity (Heil et al. 2016).
Cold water therapy: how to get started
To avoid the risks described above, the key is to start with small doses, and increase the frequency and duration of exposure gradually as your brain and body adapts. The colder the stimulus (water immersion, shower, etc.), the shorter amount of time you need to expose yourself to the cold. We are all different in the level of cold that we can tolerate. Aim for a temperature which initially feels uncomfortably cold, yet is safe to stay in for a few minutes.
If you’re entirely new to cold water immersion, simply start in the shower, and turn the temperature down low for the last 30-60 seconds. When you get out of the shower, try to let the body heat up on its own, rather than vigorously rubbing or drying yourself with a towel. This will encourage a shiver response, which is what promotes the conversion of white fat to the more metabolically active brown fat.
Once you’re happy with cold showers, you might want to try immersion in a cold bath, with or without ice. Enter the water slowly to limit the sudden shock, and focus on keeping your breathing under control. Aim to start with 1- 3 minutes, and then if this starts to feel comfortable you can increase
Aim to work towards deliberate cold exposure for 11 minutes per week in total. This is a recommendation based on a study which showed benefits in brown adipose tissue for winter swimmers who completed an average of 2-4 sessions lasting 1-5 mins each distributed across the week ( Soberg et al 2021). It is not clear whether there are additional benefits for more frequent or longer duration exposure, so 11 minutes seems a sensible target to aim for.
How can I find out more about cold water immersion therapy?
If you have any concerns about whether cold water immersion therapy is for you, speak to a medical professional before you start. I really enjoyed the Huberman Lab podcast on cold water immersion with researcher, Dr Susanna Soberg. You might also find it helpful to read about cold water therapy via the Wimhof Method.