STEVE INSKEEP, HOST:
Have you heard the old idea that a cold shower is supposed to be good for you? A plunge in an ice-filled tub is supposed to be good for you, too. I, for one, am not about to find out if this is true, but NPR's Will Stone looked into it.
RILEY SWORTZ: Ready?
AUDREY NASSAL: Yeah.
RILEY SWORTZ AND AUDREY NASSAL: One, two, three.
(SOUNDBITE OF WATER SPLASHING)
WILL STONE, BYLINE: First, there's the cold shock.
SWORTZ: Oh.
STONE: Your heart rate jumps. You gasp.
SWORTZ: Ooh.
STONE: Stress hormones are released. You feel pain on your skin, and eventually, you begin to shiver.
SWORTZ: (Laughter).
STONE: To the uninitiated, nothing about this sounds like a good idea, but show up on Sunday morning to this sandy spot in Seattle's Ballard neighborhood, and you'll hear plenty of reasons to get in.
SWORTZ: Because it's awesome.
STONE: Riley Swortz is submerged up to her shoulders. She's one of the regulars here.
SWORTZ: There's this point where you hit a level where it's not cold anymore, and this calm washes over you.
STONE: The water temperature in Puget Sound ranges from the mid-40s to mid-50s.
BEN PASCHKE: It's a great alternative to coffee.
STONE: That's Ben Paschke. Next to him is Max McFarland, who's training for a marathon.
MAX MCFARLAND: It's, like, mostly my joints. It feels like it definitely helps that just 'cause I get very sore.
STONE: Groups dedicated to cold water immersion have popped up all over. Audrey Nassal organizes this weekly gathering.
NASSAL: Any anxiety, anything I'm struggling with - it's just gone. And when I come out of the water, it's - I've left it in the water.
STONE: This cold-plunge craze is a remarkable turn of events for Francois Haman. He's at the University of Ottawa and has studied cold for more than two decades.
FRANCOIS HAMAN: I never expected this to take that direction.
STONE: Historically, the field tended to focus on the risks of cold exposure - military operations, how to survive - not so much the potential therapeutic benefits.
HAMAN: That big push towards using ice water as something that is tremendously beneficial is recent.
STONE: He says many of the popular beliefs floating out there are way ahead of the science.
HAMAN: Most of the information we have right now on the health benefits of cold exposure are based on very thin research.
STONE: You often hear that cold plunging helps the immune system and dampens whole-body inflammation, that it has tremendous effects on dopamine and other hormones or that it can treat various chronic diseases and improve mental health. All of this is plausible, but there's not much high-quality evidence coming from studies done under carefully performed conditions. There aren't any rigorous and large randomized controlled trials.
HAMAN: A lot of claims are being made and leaps of faith are being made based on absolutely nothing or just a few papers and social media.
STONE: Even the data that do exist are hard to interpret because studies use different methods, temperatures, types of cold. He compares studying cold to exercise.
HAMAN: Exercise is different intensity, different frequency, different types of exercise. Cold is exactly the same.
STONE: There's no single definition of cold plunging, or ice dipping, as some call it. Usually, it's extreme - water in the 50s or much colder. In his lab at the University of Sherbrooke, Denis Blondin mostly uses a special cooling suit so they can control the skin temperature. Their studies usually last a few hours, and it's not too cold. Think of being outdoors during late fall in the northeast with only shorts and a T-shirt. Blondin says research does show that cold exposure has some clear benefits for metabolic health, especially your ability to regulate blood sugar.
DENIS BLONDIN: We see it across the board in basically all cold exposure studies.
STONE: They also see some changes in resting heart rate and blood pressure. Blondin says these improvements may last for 24 to 48 hours after the cold exposure.
BLONDIN: So this provides an opportunity for people to do other things to improve their metabolic health and their cardiovascular health.
STONE: And while there's no indication cold exposure alone leads to weight loss, research does suggest it may help with Type 2 diabetes. There's also been tremendous interest in the role of brown fat, which gets activated by the cold and helps keep your body warm. But Blondin says it's actually your muscles that are key here, which is why you need to shiver to get these benefits.
BLONDIN: You've got these contractions that are similar to what you would have with exercise, but the difference that you have with the cold, the muscles that are recruited is kind of all over the place. It's everywhere.
STONE: What's not so clear is how much you can extrapolate these findings on metabolic health to short dips in extremely cold water. There's also some exciting research on mental health.
HEATHER MASSEY: A lot of qualitative data, a lot of anecdotal data out there that people are experiencing improvements in their mood, their mental health.
STONE: Heather Massey is at the University of Portsmouth in the U.K.
MASSEY: Now we need to work out, does it work, who it works for, and how does it work?
STONE: Massey is involved in the first major clinical trial on cold-water swimming to treat anxiety and depression. Their pilot study found the majority of people experienced improvements in their symptoms after eight sessions bobbing in the water off the coast of England. There are many theories about why this seems to help people. Massey says it could relate to that big hormonal response of getting in the water.
MASSEY: People suggest they get a - sort of a post-swim high.
STONE: Cold water also affects the autonomic nervous system, triggering your fight-or-flight response. But submerging your head stimulates the vagus nerve, which has a calming effect. There's also the idea of cross adaptation - that cold water prepares you for other stressors in life - plus the potential social benefits of being with people - in nature, overcoming a challenge. Massey says, yes, there are many open questions about the science of cold plunging.
MASSEY: I'm a cold-water swimmer myself. I'm not the fun police. I'm not trying to stop people doing it.
STONE: Do it safely, she says - ideally, with others. The cold shock can make you pass out. There's hypothermia and cold injuries. Francois Haman says there's no single protocol, no number of minutes or temperatures, that's proven to give the maximum benefits. He only gets in extremely cold water a few times a month, and not for that long. His goal is to build resilience.
HAMAN: To control my emotions even though I'm facing a stress that is extremely painful.
STONE: But he says doing this every day can be too much stress on the body. Instead, he likes to take a cold shower or get into a bathtub with chilly water around 70 degrees.
HAMAN: Just like people would take a coffee - for me, the cold water becomes that coffee.
(SOUNDBITE OF WATER SPLASHING)
STONE: On the beach in Seattle, Audrey Nassal says, she started cold plunging to deal with the stress of the pandemic, and it stuck.
NASSAL: Especially when I have a bad week, I'm just, like, going to go plunge. I need a reset.
STONE: A reset that science hopes to learn more about soon. Will Stone, NPR News.
(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.
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