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Cold water immersion is nothing new

The supposed benefits of cold water have been touted since antiquity. Hippocrates believed it eased patient's weariness, the Romans used a 'cold sauna' known as a frigidarium after taking hot baths and, of course, the Victorians took to the water at spots like Brighton and Penzance. Nowadays, the practice goes by the more scientific-sounding name 'cold water therapy' or 'cold water immersion'.

The shock of cold water is your body protecting itself

To trigger that stunningly cold feeling, Greg took a dip in a brisk 12°C modern therapy bath. As Professor Mike Tipton explains: “As your skin temperature falls, there are cold receptors about 0.18mm below the surface of the skin that are firing like mad.” The cascade of physiological responses that result can be termed 'cold shock'.

Most of these effects are intended to preserve body warmth. Shivering generates heat, but leads to gasping and uncontrolled breathing. Shutting down blood flow to the skin and extremities keeps vital organs warm, but causes numbness. Heart rate and blood pressure shoot up to get blood moving, but make us panic. Going any further than these initial effects is overdoing it. The idea that a longer ice bath is better is often cited by cold water immersion advocates; Prof Mike Tipton thinks that’s not only dangerous but completely unfounded.

Cold water immersion may slow down muscle growth

Despite a plethora of studies, the science isn't clear on whether cold water immersion helps recover after exercise. People's perception of muscle soreness seems to reduce, and there is some evidence that people recover their strength faster, but these effects only occur when compared to doing nothing at all. A more traditional 'warm down' technique is just as effective if not doing exercise the next day.

More worryingly, cold water immersion may actually inhibit muscle growth – a massive issue for gym-goers using this technique after a workout. One hypothesis suggests that cold shock puts a hydrostatic squeeze on muscles to reduce inflammation of the tissue, stymying the muscle's ability to repair itself. Additionally, cold water immersion slows down the enzymes and satellite cells that build muscle.

Reducing inflammation helps treat depression

One surprising benefit of cold water immersion's anti-inflammatory effects could be better mental health. Mike notes: “If you get a high level of inflammatory cytokines… it inhibits the pathway for the release of serotonin, which is one of the hormones that makes you feel good.” Hence, decreasing these cytokines through cold water immersion can help treat depression. Improved mental health is the most well-founded effect of cold water immersion

Ice baths don't help stress or circulation in the long-term

Cold water immersion is obviously stressful in the moment, but advocates claim that long-term cold water immersion will reduce stress overall. Greg did notice a pep in his step after his dip, but this is actually a stress response. The body is releasing fight-or-flight hormones such as adrenaline, noradrenaline and cortisol to fight back against the chill. On the other hand, shivering from the cold uses deep skeletal muscle that is usually relaxed. This tires us out and helps us get to sleep more easily at night. And a good night's rest is known to decrease stress levels.

Cold water immersion's effect on circulation is similarly a mixed bag. In the long-term, there's no evidence that repeated constriction of the blood vessels helps circulation. Short-term decreases in blood flow to the extremities can cause a range of injuries, however. In severe cases, frostbite will affect the fingers and toes due to this effect. But Mike warns that even shorter periods can cause smaller non-freezing cold injuries where the “blood flow is shut off long enough to damage the small vessels and nerves of tissue”.

Plunging into cold water can be deadly

Many of the other dangers of cold water immersion are caused by poor guidance on the technique.

Firstly, there's no need for ice at all – Greg's 12°C bath is plenty cold enough. Mike's own studies have found that “the physiological response to cold water peaks somewhere between 10-15°C”. Going below that only increases risk with no further benefit.

Secondly, cold shock can catch the healthiest people off-guard. Cardiovascular issues or burst aneurysms can occur faster than hypothermia – that's why even proficient swimmers have been reported dying just minutes from refuge. Once uncontrollable breathing overcomes someone, they can panic. If you’re ever in this scenario, get your breathing back under control before trying to move.

Long-term cold exposure weakens your immune system

One of the stranger claims of cold water immersion is that it boosts your immune system, a theory popularised by Dutch extreme athlete Wim Hof. Wim is an advocate for long-term cold exposure. He’s stood covered in ice cubes for two hours and ran a half-marathon in the Arctic. Although a paper was published based on Wim's feats, the link to increased immune health isn't so clear-cut.

Defining immune function is an issue in the first place. One might measure the number of immune cells such as leukocytes and neutrophils. Or, one might measure the number of upper respiratory tract infections over time. In fact one paper doing the latter found that all swimmers, regardless of water temperature, had fewer infections. Mike reports the science is certain on one thing: “As you get longer immersions and cool more profoundly, that definitely impairs the immune system”.

Open water swimmers in a lake in Cornwall.

Open water swimming is a safer alternative to ice baths

Given the potential risks of ice baths, it's worth looking at some safer alternatives to cold water immersion.

There have been studies that showed that just 30 seconds of cold water at the end of a hot shower led to fewer sick days. Showers don't produce as strong of a cold shock as immersion however, because the skin-to-water contact area is smaller.

Open water swimming solves that problem and addresses many of Mike's main concerns. It's not as cold as an ice bath, if you swim with friends there are other people in case of emergency and open water swimming has more evidence that it actually works on improving participants' wellbeing. It's worth noting that the temperature of the water isn't necessarily the main cause; it could simply be the social interaction or the exercise itself.

With alternatives like these, ice baths may not be worth putting your body at risk for. But if you do want to try it out, stick to a 12°C bath and stay in for no longer than a few minutes.

To find out what listener Laura made of Greg's cold water findings, listen to the whole episode in full on 麻豆约拍 Sounds.

The information contained in this article was correct at the time of broadcast on 9 November, 2023.