Cold-water immersion may offer health benefits -- and also presents risks

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Dr. Mark Harper recalls his first cold-water swim in the south of England 20 years ago. It was August, but the initial jolt from the plunge took his breath away.

The shock to his system lasted a minute or two until he was “recombobulated and able to think about something other than the cold," Harper says. A surprise sensation soon replaced his discomfort.

“I remember getting out of the water the first time and feeling so good," Harper, an anesthesiologist who has since researched the potential risks and rewards of taking a nippy dunk. "I wasn't expecting that.”

Claims about the benefits of cold-water immersion date back centuries. Thomas Jefferson, the principal author of the Declaration of Independence and the third American president, wrote toward the end of his life about using a cold foot bath daily for 60 years. He also owned a book published in 1706 on the history of cold-water bathing.

While evidence is building around the positive health effects of swimming in chilly water, bathing in ice or taking cold showers, scientific confirmation is still lacking.

But Harper, who became a regular cold-water swimmer after his initiation, said there are strong signs that people can derive mental health benefits from the activity. He mentioned a positive effect on depression and general well-being.

“For now, we have a very strong base, but not hard evidence, that cold-water immersion is effective for mental health," Harper told The Associated Press.

Harper said his own early experiences with cold-water swimming piqued his professional curiosity. As a physician, he wondered if the brief bodily shock had clinical uses for treating depression. He cited the biological phenomenon of hormesis, in which a stressor introduced at a low dose creates a positive response.

Muscles and bones put under stress —for example, with weight-bearing exercise — also respond and grow.

Harper acknowledged that the positive effects he's observed may be the result of the placebo effect, a phenomenon in which people who are given a medicine they think will help them report responding to the treatment even if it had no active ingredients.

In the case of cold-water immersion, the benefits may come from meeting people, the exercise itself, or simply accepting a challenge and accomplishing it, which improves self-confidence, he said.

“Personally, I think it’s all of those things, and the cold has an additive effect,” Harper said. “I think we have a good physiological basis for that. The basic science tells us the cold has a very strong effect on the body.

“What we’re talking about is an intervention, when it's used clinically, that produces beneficial effects on mental health. So in a way it doesn’t matter which aspect is generating the positive effects.”

Harper cited what he said was a common reaction among first-timers who have taken the plunge.

They often say “the fact that I’ve done this means I can do anything,” he said. “It’s quite a confidence builder and it’s something people stick to because they enjoy it so much.”

Dr. Mike Tipton, a physiologist at the University of Portsmouth in England who has studied extreme environments, authored a paper along with Harper and two more researchers several years ago. The title highlighted the potential advantages and dangers of stimulating the body with a sudden drop in temperature: “Cold Water Immersion: Kill or Cure.”

“Like other environmental constituents such as pressure, heat and oxygen, cold water can be either good or bad, threat or treatment depending on circumstance,” they wrote after reviewing the research then available on the topic.

One of their findings: The activity presents dangers. Deaths from cold-water immersion are not uncommon. The shock of frigid water can cause people to hyperventilate and drown. But Tipton told The AP the risks can be managed with common sense and precautions.

You do not need to go to extremes to get a potential payoff. Entering water at a temperature of 20-15 degrees Celsius (68-59F) and staying for only a few minutes is sufficient.

Tipton explained if the water is colder than that, you may get more benefit — but limit your exposure.

“If you ask me what protocol you would follow if you thought this was going to be doing you good, I wouldn't go in water much below 12C (54F), and I wouldn’t stay in for much more than two minutes,” Tipton said.

Tipton and Harper both said that any benefits from cold-water immersion come from the body's cold-shock response: the sudden fall of skin temperature, the release of the stress hormones, the release of endorphins, and the anti-inflammatory effect.

Tipton cautioned against long spells in an ice bath.

“Sitting in water for as long as I can fills me with horror,” Tipton said. "This could destroy small nerves, blood vessels in extremities and could result in amputation the same way frostbite can."

Harper, who has swum as long as four-hour stretches in open water, advised vigilance.

“People think it’s got to be super cold, super long and the longer the better,” Harper said, "and that’s wrong.”

Tipton said he's not trying to be the “fun police” but suggested caution and a medical screening if you take the plunge. He said humans are considered “tropical animals” who need to adapt to the cold and are better suited to warm conditions.

A human’s resting body temperature is about 36.5 to 37.5 degrees Celsius (97.7 to 99.5F). Because of that, cold-water immersion is stressful and carries risks for the cardiovascular and respiratory systems. Not to mention the risk of drowning.

“We don’t want to stop people doing it, but we want to make sure they do it in a way that maximizes the benefits and minimizes the risks,” Tipton said.

He suggested swimming in a life-guarded area, or going with experienced outdoor swimmers. He also suggested knowing the body of water you're swimming in. Hazards, among others, include tides, temperature, depth and pollution.

“Understand that taking a tropical animal and putting it in cold water is probably the greatest stress that most people will experience in their life,” Tipton said.

He suggested entering the water in a controlled fashion instead of jumping in.

"Be sensible about it,” he said. “Incremental is the key.”