a A cold shower a day keeps the doctor away, according to Wim Hof, the Dutch extreme athlete and self-proclaimed Iceman. For Hof and other advocates, cold water immersion is a miracle cure for conditions from arthritis and Crohn’s disease to depression and headaches.
But the death of Kellie Poole, a 39-year-old whose heart stopped during a cold water immersion therapy session in Derbyshire last year, has raised questions about the safety of diving into ice-cold water, with the coroner this week raising concerns the lack of regulation.
Do the purported health and wellness benefits of cold water immersion outweigh the risks?
“One of the main positive qualities people claim is that it wakes you up, sets you up for the day and makes you feel revived,” says Prof. Mike Tipton of the University of Portsmouth’s Extreme Environments Laboratory. “And it’s not surprising that immersing a tropical animal, as we are, in cold water will surprise them.”
This feeling of alertness is caused by the cold shock response, in which a sudden drop in skin temperature immediately after immersion causes a rise in adrenaline, noradrenaline and cortisol. People will have their own opinions about whether diving into a cold pond is a positive, rejuvenating experience, but if this is the benefit you’re looking for, a two-minute immersion is sufficient, Tipton says. There is no need to spend hours in an ice bath. “The longer you stay indoors, the more likely you are to be exposed to disadvantages such as hypothermia,” he said.
Some claim more lasting mental health benefits, which Tipton says are plausible but largely anecdotal at this stage. His lab oversaw immersion sessions for a woman with severe depression, for example, crediting them for her recovery.
There are also suggestions of broader physical benefits for the immune system and anti-inflammatory effects. A Dutch study with 3,000 participants showed that people who took a cold shower daily (after a hot shower) were sick 29% less often than those who only took a warm shower. But this study looked at the outcome rather than the physiological mechanisms.
Tipton and colleagues also tried to study the potential benefits and found that people who went swimming outdoors had fewer respiratory infections than their partners who were not swimmers, but the same benefits were seen in people who went swimming indoors.
“There is evidence of benefits, but we are in the realm of snake oil if you start telling people it is a cure that will solve all your problems,” he added.
The physiological effects of the cold shock response can also be dangerous. The sudden cooling causes a sharp gasp, followed by a period of uncontrolled hyperventilation. “A full breath can be 2 to 3 liters and a lethal dose of water is 1.5 liters,” Tipton said. “You may have crossed the lethal dose of water to drown before you come back to the surface.”
At the same time, the cold shock response causes the heart rate to increase and the peripheral blood vessels to close. “It’s like turning off all your radiators and turning up the heating at the same time,” says Tipton. “Blood pressure increases, which is dangerous for people with high blood pressure.”
About 60% of cold water immersion deaths occur within the first minutes of immersion. That’s why scientists recommend doing as little as possible (floating or standing) for the first few minutes in the water, after which the response to the cold shock decreases.
There is also a difference in the physiological effects depending on whether the face goes into the water. While the cold shock response is activated by sensors on the body’s skin, receptors on the face activate the so-called “dive response,” which slows the heart rate. When a person puts their face in a bowl of water, their heart rate may slow to just 25 or 30 beats per minute.
During a full-body dive, the heart has competing inputs that simultaneously tell it to speed up and slow down, which, according to one study, caused an arrhythmia in about 80% of volunteers who dove underwater for a 10-second breathing pause. In most cases this is harmless, but for people with pre-existing heart conditions this can become a more serious episode.
Much of the risk can be reduced by a progressive approach to cold water immersion, according to Prof Greg Whyte of Liverpool John Moores University, who has developed a two-week cold water exposure plan. Sponge for divingwith the Royal Life Saving Society (RLSS).
The body habituates to the cold shock response, with just five two-minute immersions reducing the physiological response by as much as 50%, and the habituation appears to last several months. The uninitiated are advised to start with facial immersion or a cold shower before attempting full immersion or an outdoor swim.
“It’s really about a progressive approach,” said Whyte. “There has been a worrying trend of people diving headlong into it… and some TV shows have glorified and sensationalized that.”
Whyte believes the marginal evidence for the health benefits of cold water immersion reflects this being a new area of research rather than a lack of credibility. “We can be reasonably confident that there are health benefits – not just in terms of physical and mental health, but, because it is often a community activity, in terms of social health. But it is always emphasized by the fact that you have to do it safely.”