Taking the plunge into cold-water immersion

Immersing yourself in cold water has many health benefits, as Anne Gastinger discovers. 


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My grandfather first introduced me to the sea when I was a toddler. I remember him holding me steady as we braced against the surf’s edge on Hokitika Beach, foam-flecked water swirling around our feet. It was all good fun until the ebb of the Tasman Sea gouged the sand from under our soles, leaving me petrified and my grandfather having to deal with the tears.  

This childhood memory periodically returns when I’m swimming in the sea or inland in lakes and rivers. The mercurial temperaments of these environments demand our vigilance and respect. Even so, Aotearoa’s raw nature abounds in swimming spots ideal for an invigorating dip on fair weather days. As well as the exhilarating thrill, swimming in cold wild water is of great benefit to our wellbeing. 

Relief for migraines

Migraines have plagued me since adulthood. In the first years when the pain would begin I’d hunker under the bed covers in a quiet darkened room with a cold flannel over my forehead. Taking a soothing shower also brought momentary relief but there seemed no avoiding the long, gruelling hours ahead until the episode passed. Or so I thought, until I was caught out with a migraine during a long car trip with my older brother. Pulling the car into a clearing by the Motueka River, my brother suggested I rest in the river shallows. The cool water flowing over me did help. The pain eased and we were able to travel on.  

I now swim regularly through the spring, summer and autumn months at my local beach. During winter my attendance rate is poor but I’m working on that, because bathing in nature’s cold waters alleviates the frequency and intensity of my migraines.  

Tips for cold dips 

When swimming in water 16ºC or colder, take note of the following.  If you have an underlying health condition, first seek medical advice. 

  • Check weather conditions and ensure the location and water quality are suitable for swimming. 
  • Start with short dips and wade in slowly. It feels painful, but the body adjusts. Learn your limits, and swim with others.  
  • Head under or not? Keep your face above water until breathing is under control. Cold water frequently entering the ear canal can cause an abnormal bone growth commonly known as surfer’s ear. Protect your ears by wearing a silicone swimming hat and/or ear plugs. 
  • Beware of hypothermia, which occurs when body temperature falls below 35ºC. If you slow down or shiver, get out and warm up. The length of time you can swim in cold water without hypothermia depends on body size and shape, experience and training. 
  • When to get out? Practice caution. Experienced swimmers: 10 minutes for health benefits. 

The feel-good factor

In recent years the time-honoured practice of swimming in cold wild waters has gained momentum as word spreads about its energising, stress-relieving and mood-enhancing benefits.  

Kerry Newton is the founder of Ōtautahi-based Scarborough Dippers. She started her group in 2017 with four members, aiming to complete the Wet July daily sea-swim challenge as a fundraiser for charity. The experience proved so successful that membership now tops 30, with ages ranging from 20 to 80 plus.  

The Scarborough Dippers swim year-round, even through winter months in Canterbury when water temperatures hover around 9ºC. Kerry believes the popularity of the Scarborough Dippers is due to “the social contact, the feel-good factor and the improved immunity against getting colds”. 

When stress can strengthen

The health claims of cold-water dipping have garnered attention in the scientific community. While there are serious risks if one does not adhere to safety guidelines, the evidence emerging about the adaptions our body undergoes when stressed by cold water is compelling. So much so that Grant Schofield, a professor of public health at Auckland University of Technology and himself a daily cold-water dipper, describes the practice as “effectively upgrading your brain”.  

“Cold water is stressful on the body. Under stress we build back even better than we started,” Professor Schofield said on Radio NZ in August 2021, and confirmed his comments when contacted by Organic NZ

“Some of these beneficial adaptions include the conversion of white fat to beneficial more metabolically active brown fat, and increased secretion of the hormone irisine from the muscles which aids glucose and fat metabolism. These changes are adaptations to the stress of the cold and they help the mind and body be a more efficient version of itself.” 

The Scarborough dippers braving the cold water on a Canterbury winter’s day at Te Onepoto – Taylors Mistake Bay

Mental health gains 

There are also mental health gains from cold-water swimming, Professor Schofield says. “Cold-water immersion helps remove and regulate a neurotransmitter, glutamate, that is implicated in depression and anxiety and up-regulates GABA (an inhibitory neurotransmitter), so you have a feeling of calmness.”  

Researchers in the UK showcased this effect by helping a woman suffering from long-term severe depression to manage her health medication-free just by taking weekly cold-water swims. When immersed in chilly water at temperatures of 14ºC, the body creates over five times its normal level of noradrenaline (a neurotransmitter that prepares the body for action) and more than doubles levels of the feelgood neurotransmitter dopamine, Czech researchers discovered. This increase in chemicals crucial for healthy brain function might explain the post-cold-swim euphoria many swimmers feel. 

Depression, arthritis, dementia 

Not only can cold-water exposure combat depression, it has also been shown to boost energy, aid cognition and relieve arthritis. One study found that regular winter dippers in Finland reported experiencing less tension and fatigue, improved mood and memory, and less arthritic pain. Another study of cold-water swimmers in Germany found they contracted significantly fewer respiratory infections than the general population. 

At a time when dementia in Western societies is on the increase, cold-water bathing may yet prove a means of delaying or even preventing its onset. In 2018 researchers in the UK found cold-water swimmers who regularly lower their body temperatures to 35ºC produce a ‘cold-shock’ protein, known as RNA-binding protein 3 (RBM3). This protein has been shown not only to slow the onset of dementia in mice, but even repair some of the damage caused by the disease. 

Double dip with forest bathing

The Southern Pacific waters surrounding our shoreline are ideal for cold-water bathing. Inland we have many rivers and lakes lined with native bush, some still in pristine condition. Bathing in these wild waters is in a sense double-dipping in terms of health rewards.  

Peter Wohlleben, German forester and bestselling author, explains why in his latest book The Heartbeat of Trees. Trees, he tells us, release compounds into the air in order to communicate among themselves. These arboreal chemicals are an elixir for our health.  

The evidence is so compelling that Japanese doctors issue prescriptions to their patients for ‘forest bathing’, called shinrin-yoku. When walking in the bush or swimming in rivers and lakes surrounded by healthy, diverse forest, the arboreal compounds we inhale aid our circulatory system and lower our blood pressure. Trees produce protective antimicrobial phytoncides to ward off fungal attacks. These help allergy sufferers and reduce inflammation in the human body. 

Furthermore, forest bathing may have a protective effect against cancer. Japanese researchers compared a group of people who went forest bathing with a group who did a city walk. They found that the forest bathers had an increase in cancer-killing cells and anti-cancer proteins. ‘The elevated concentrations of both can be detected in … blood up to seven days after the forest walk.’  

Korean researchers examining this phenomenon discovered that elderly female forest bathers’ blood pressure, lung capacity and artery elasticity all improved significantly more than their sister city walkers. This is all good news for those taking a walk, tramp, or bike ride through the bush en route to a river or lake swim. 

Acclimatise and stay safe 

For those new to cold-water dipping, summertime when marine, river and lake temperatures are warmer is an ideal time to begin acclimatising your body to cold-water shock. This is our initial breath-gasping stress response to the sudden drop in skin temperature caused by the cold water. The quickened breathing rate, along with an increase in blood pressure, lasts some minutes. As we acclimatise – which can occur after as few as six cold-water swims – our bodies adapt to better withstand cold temperatures. 

After leaving the water, dry and dress yourself quickly in warm garments that are easy to slip on. It’s not uncommon ten or so minutes afterwards to get the shivers as ‘after drop’ kicks in. When cold, the body cleverly protects its vital core organs by reducing blood flow to the skin and limbs. Our core stays warm while our extremities cool. Back on land when peripheral vasoconstriction ends, the cooler blood mixes with the warmer blood, causing a drop in deep body temperature. Be prepared with a hot drink in a thermos for afterwards.  

Healthy habits

Cold-water swimming, when practised according to safety guidelines, is an effective means of aiding and maintaining health. As Professor Schofield says: “We’re such great adapters, we un-adapt at the same rate if we’re sedentary.” Like all good health practices it works best if undertaken regularly. 

Anne Gastinger lives, gardens and writes in Ōtautahi Christchurch, and enjoys swimming at Waimairi Beach.  

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