From blood sugar control to mental health and brain cell benefits, research suggests an icy plunge may be a fad that floats.
Historians can’t pinpoint when humans first learnt to swim, but 100,000 years since the possible first buoyant immersion, scientists are now toiling to determine whether a bracing dip is a magic bullet for human health.
Though sceptics deride the social-media rebranding of swimming in the sea, lakes and rivers as “wild” or “cold”, more and more research suggests the growing trend for cold water immersion (CWI) triggers a set of extremely beneficial reactions in the body.
At the very least, CWI can slash one’s power bills. Dougal Dunlop, 70, can chart how his daily swims in Wellington’s never-temperate Oriental Bay have over the years have made him near-immune to the cold. “I don’t need to turn the heater on,” he says, and laughs at the idea of wearing a wetsuit for swimming, even in midwinter.
Rachel Averill, his friend in the Washing Machines sea swimming group he leads, agrees. “I’ll be in short sleeves in the office when everyone else thinks it’s freezing.”
The growing popularity of wild swimming could also reduce New Zealand’s alarming incidence of drowning. With fewer schools having access to pools to teach children swimming, the growing availability of well-organised local sea swimming groups might be able to close the gap. Washing Machines welcomes children, who swim under the supervision of grown-ups, including Dunlop, who is a professional swimming coach.
But it’s the metabolic and other physical effects of CWI that have turbocharged its popularity. Pure logic suggests swimming is a healthy activity and demonstrably makes people feel good. But a recent deep dive into the known science of mammalian thermal adaptation by respected science authorities has generated extra excitement that CWI could be a fearsome weapon against diabetes, heart disease, depression, auto-immune conditions, menopause symptoms, inflammation and much else.
As a modern movement, cold swimming is no mere pandemic fad. Sports followers have for decades admired the stamina of extreme-cold distance swimmer Lynne Cox, whose 1987 swim between the United States and Soviet Union, crossing the Bering Strait, was credited with defrosting Cold War tensions. Another exemplar is Lewis Pugh, who, among other feats, swam across the North Pole in 2007.
More recently, the developed world’s quest for mindfulness, reconnection with nature, rewilding, green bathing and the like has also snagged on “wild swimming” as a free, feel-good and healthy pastime.
Come the pandemic, exponentially more people had the time to try it, with the bonus of it being a solitary activity, allowable under social-distancing rules – though not initially in New Zealand. Dunlop and some of his Washing Machines cohort were chased by a police launch during the first lockdown and told to desist, as the initial restrictions envisaged sea swimming as too dangerous, and likely to stretch resources. He says it was a very difficult few weeks of being denied their passion.
The question remains: How much is it a healthy passion and how much a health panacea? Dozens of scientific studies tantalise with possible benefits, but overall, the evidence remains inconclusive.
Pure observation of all those elated, glowing swimmers emerging from the water puts it in the When Harry Met Sally realm: shouldn’t everybody have what they’re having?
Swimming is demonstrably good for muscles and joints, and helps with blood pressure and the lymphatic system, as with any moderately strenuous exercise. Adding a serving of ice, however, remains a scientific point of speculation.
There’s no argument that a slew of complex physiological and chemical changes occur when mammals are exposed to the cold, but adaptive thermogenesis, or heat production, is an evolving sphere of study.
It’s known that fat-storing brown adipose tissue has a critical role in swiftly dissipating chemical energy to produce heat, a process known as nonshivering thermogenesis. Brown fat – as opposed to white fat – is the body’s metabolic good guy. It breaks down blood sugar and fat molecules and turns them into heat to help maintain body temperature. Cold temperatures are one of its triggers. Alas, most body fat is white, and is where extra energy gets stored, often at a damaging level for health.
But CWI studies suggest the picture may be more nuanced than that, because lurking in the white fat, there’s also beige fat, an additional thermogenic adipocyte that appears to provide a more lasting warming response to extreme temperatures than brown fat. Epidemiologists are understandably excited about the possibility that summoning up a beige superpower via regular cold exposure could carry lifesaving metabolic health benefits, chiefly in fighting insulin resistance. Then again, one Polish university study compared a group of cold-water swimmers and a group of indoor-pool swimmers and found no differences between the two over six months.
Results may vary according to numerous factors: the body composition of the swimmer, other underlying health factors, age and gender, the temperature, the person’s habituation to cold, even the degree of salination in the sea.
Dunlop figured out salination was the factor that explained why, after years of pool swimming, his badly injured back improved only after he took up sea swimming. “The salt makes you more buoyant, so my body is in a better posture when I swim.”
Autoimmune benefits
The challenges in assessing the existing research on the benefits or otherwise of cold-water exposure are several-fold. Some of the most promising findings have emerged from research using mice, not yet replicated with humans. So far, only small groups of human subjects have been tested, often without a control group.
It’s of limited scientific use to study habitual cold-water swimmers alone, because, given the discipline they exert in their peculiarly challenging habit, chances are they’re healthy in a lot of their other habits as well. Their wider lifestyles, rather than the cold exposure, may account for their healthy lipid and metabolic profiles.
It seems for every promising result in more than 100 reputable studies of CWI, there’s another that calls its benefits into question. While some trials have found elevated white blood cell counts suggesting improved autoimmunity in groups of cold swimmers, others have observed troponins, which are markers suggesting heart damage.
There has been no large-scale, randomised, controlled study yet, and Norwegian academics who recently audited existing research have called for one. In findings published in the International Journal of Circumpolar Health, they say there is increasing scientific support that exposure to cold water may have some beneficial health effects.
“There are several specific areas regarding the potential preventive health effect of CWI that need further investigation. For example, its effect on the immune system (for instance, tolerance to stress and respiratory infections), potential prophylactic effects on the cardiovascular system and prophylaxis against insulin resistance and improved insulin sensitivity and mental health are areas that are promising and warrant further investigation.”
This study collation contained encouraging snapshots from research so far, including that women may benefit more. The body composition and insulin sensitivity of 30 CWI swimmers were examined for six months alongside a control group. The swimmers were overweight compared with the control group and had higher body-fat percentages. The female swimmers and those of either sex with lower body-fat percentages experienced positive effects on their insulin regulation.
This small study also suggested a correlation with pain tolerance, as measured in the response of the swimmers’ catecholamine or stress hormones, such as cortisol and norepinephrine. “Regular … winter swimming resulted in a decrease in the concentration of catecholamines when measured immediately after immersion. It was concluded that adaptation through habitual exposure to the cold of winter swimming weakened the physiological response and inhibited the rise of the catecholamines.”
Stress therapy
Then there are the possible mental health benefits, which cold swimmers swear by. It’s long been known that exercising reasonably vigorously produces the “runners’ high” chemical signallers, endorphins. But researchers in one study measured bodies’ stress responses to cold swimming and found an increase in three hormones and neurotransmitters positively linked to mental wellbeing and brain development. Purposely exposing oneself to more plasma noradrenaline, for instance, may sound alarming in layman’s terms, but it appears the brain “likes” to be stressed in some circumstances, and feels better for it.
Still, the scientist’s brain needs more input until it’s happy. The researchers said cold exposure may have an antidepressive effect, “however, the testing did not include a significant number of participants to make a firm conclusion”. They did cite an individual case study from the trial, of a woman with severe postpartum depression feeling able to cease her medication after regular CWI.
A Cambridge University study in 2020 found a group of frequent cold swimmers in London had elevated levels of a protein, RBM3, which is associated with regenerating connections between cells in the brain, and postulated CWI could be a valuable weapon against dementia. The rise in CWI’s popularity among menopausal women may also be linked to concerns about brain cell death, a common side effect of menopause’s decrease of oestrogen.
Weight loss? Tick – at least provisionally. The University of Copenhagen found that men who swam in cold water (typically 1-9°C in the Danish winter) burnt an average 500 more calories a day than people who did not. Over time, that could add up to serious weight loss.
The Norwegian scientists’ aggregation of studies concluded CWI did appear to reduce and/or transform body fat, reduce insulin resistance and improve insulin sensitivity. Accordingly, it may have a protective effect against obesity, cardiovascular and other metabolic diseases and could have prophylactic health effects. But again, wider studies, randomised and controlled, were called for.
The jaws effect
Meanwhile, the advice of sea swimmers generally is, as the self-help book said, feel the fear and do it anyway.
The safety risks are considerable, but manageable. Swimming in groups is recommended. Many of the Washing Machines take fluorescent floating safety buoys, known as tow floats. They give the swimmer extra visibility, and some models can hold keys, phones and the like, and will support enough weight to allow for a bit of a rest.
Nearly 50 years on, the movie Jaws is still doing its bit to keep nervous people out of the sea, but Averill reckons that fear can be readily overcome. Oriental Bay swimmers are far more likely to need to steer clear of the occasional dolphin or orca pod and seal. Very small sharks are in evidence, but generally, everything in the bay minds its own business. The Washing Machines have had no scares that she’s aware of.
As with rips, local knowledge is the key to understanding what might be out there. Shark scientist Dr Riley Elliott is tracking great whites in a study for the Ministry for Primary Industries, with the aim of learning more about their movements and behaviour so as to enable people and boats to steer clear of them. Increased sightings in Tauranga and Bowentown harbours have caused anxiety, following the death of a young woman at Waihi Beach in 2021. Shark attacks are extremely rare, and marine biologists say despite their fearsome reputation, sharks are more likely to be shy or merely curious than to attack humans.
Exposure by degrees
The other obvious risk is hypothermia. Some British lidos have recently reported weekly emergencies as swimmers discount the risk of plunging winter temperatures and have to be rescued and revived. The anecdotal rule of thumb among swimmers is one minute’s exposure per degree of cold, but that’s not a reliable guide. People are advised to build up cold water immersion gradually, and shorten exposure on very cold days. As with any new exercise endeavour, people are advised to seek medical advice about whether CWI could aggravate a health condition.
One adverse aspect to CWI that New Zealand has avoided is the polarising effect it has had in the Northern Hemisphere, plagued with miserably high energy bills during its current winter, thanks to Russia’s invasion of Ukraine and subsequent fuel shortages. Scarcely a week passes without furious media commentary either deriding those showing off in icy waters while even comfortably-off people freeze in their homes, or alternatively, exhorting others to take the icy plunge in order to combat this historically severe case of multinational winter depression.
Giles Coren of the Times recently expressed exasperation at the perceived smugness of cold swimmers, saying, “You swim cold because you feel good. Which is fine, but stop making ridiculous claims for it and, please, get out before you die.”
But colleague Anna Maxted put it like this: “You lower yourself into the bitingly cold water, stressed and tense – and every open browser tab in your mind shuts down.”
Cold comforts
Fashionable accessories and subscription courses are surfacing as the fad enters the mainstream.
Water and ice may be as old as time and freely accessible, but never doubt that they’ve been ingeniously monetised through the growing enthusiasm for cold-water swimming.
There are specially designed garments for the pre- and après-swim, including for dogs, and ranges of accessories. Some, notably the Dry Robe range of coats and bags and the Wylding boiler suit, have also evolved to become fashion items overseas – partly because they’re warm and wick away chilling water, but also possibly because they advertise one’s hardcore tendencies.
The hobby is also finding its way into novels, such as Jess Ryder’s recent thriller, My Husband’s Lover, in which a hitherto cosy women’s cold swimming group goes a bit feral by a remote Scottish Highlands lock.
Hollywood grande dame Katharine Hepburn swore by CWI. It has also passed muster with film star Gwyneth Paltrow’s Goop Lab and bestselling self-help author Mel Robbins, and has an occasional fan in US President Joe Biden, who likes a Thanksgiving dip in Nantucket.
There are also online subscription courses offering to teach people how to do it all properly, which causes endless amusement to the hardy souls who just get into the water without any particular method.
A prime populariser of “method” cold swimming is a Viking-esque Dutchman, Wim Hof, a champion athlete who has devised a breathing and meditation method that, he says, optimises CWI’s benefits. At 63, a former world record-holder for under-ice swimming and numerous other cold endurance events, Hof is a strappingly good advertisement for his system. He evolved it in the best traditions of sharing something he believed had made him healthier – even though the medical establishment has greeted his claims as a combination of pseudo-science, common sense and suggestions unlikely to harm people unless carried out recklessly.
Having spent decades extending his thermogenic superpowers, Hof once held the world record for longest time in direct, full-body contact with ice: 1 hour, 44 minutes in January 2010 – paradoxically, a stunt to raise awareness of global warming. That record has been superseded, now standing at 3 hr, 28 sec – hardly a goal most health seekers would aspire to.
However, Hof’s programme has been research tested and, as with the existing body of research on CWI, his claims for it have not been debunked outright. One study, for instance, found its effects could have important implications for treating inflammatory conditions such as autoimmune disease; another that it offered no benefits for young, elite male athletes. Analysts conceded that it could help guard against altitude sickness in mountaineers, after a 2014 experiment on Mt Kilimanjaro.
Wellington swimmer Rachel Averill, a biochemist who now works for the Royal Society Te Apārangi as an administrator, says the research so far is exciting, but her motivation remains based on incontrovertible empirical self-observation. “It makes me feel fantastic. It’s definitely addictive. People I work with can tell when I get in in the morning whether I’ve had a swim or not.”
As for dedicated CWI kit, she says she’s yet to detect much uptake of it in New Zealand. The accessibility of changing rooms may be a factor, but it’s likely mostly down to the more moderate climate here. Northern Hemisphere winters are much harsher, so the protection of a fleece-lined boiler suit or a thermally insulated tent coat to change in and wear protectively afterward makes sense, but might be overkill here.
A dividing point remains the wetsuit. Like many sea swimmers, Averill began with that added protection, as exposure to Wellington’s harbour after habituation to a nice tepid pool is seldom an inviting prospect to begin with. But, in what the Washing Machines find is a common evolution, she stopped wearing it in warmer temperatures and has never put it back on.
A critical factor every dedicated swimmer emphasises is awareness of local conditions, starting with pollution. Averill says heavy rain ramps up the chances of sewage leaks, something well known to Wellingtonians in recent years.
Awareness of rips is also essential, as even benign-looking stretches of water can be deceptive. Wellington lobbyist Mark Unsworth, who has swum in the harbour for years with his golden retriever, Zara, says he has been deterred by rips in a few places, notably a strong undertow in the stretch from Breaker Bay to Moa Point. “I once decided to swim out to the island at Island Bay – not a big swim, but after 10 minutes, I found myself being swept out the channel.”
A lesser potential hazard, mostly found abroad: corny swimming group names. The Washing Machines were christened with typical Kiwi self-deprecation after an onlooker described Dunlop swimming with a friend as looking like an agitator washing machine due to their not-very-slick, slightly lop-sided strokes, splashily mirroring one another across the harbour.
Overseas, however, groups are often “mermaids”, such as Britain’s Wild and Scilly Mermaids, or worse, rejoice in handles like Vermont’s Red Hot Chilly Dippers and the Ballyronan Bluetits.