The potential health benefits of cold plunging

Over the last few years, cold plunging has grown significantly in popularity, with many participants describing "powerful, even transformative effects on their state of mind and sense of wellbeing," Stone writes. Cold plunging can take place in a cold lake, the ocean, or even just an ice bath in someone's backyard.

Because cold is one of the most powerful natural stressors, our "physiological responses will always be extremely strong," said François Haman, a professor at the University of Ottawa who has studied cold exposure for over 20 years. Some of the purported health benefits of cold plunging include:

• Regulating blood sugar
• Boosting immunity
• Reducing chronic inflammation
• Reducing anxiety and depression
• Managing stress responses
• Helping workout recovery
• Boosting brown fat to increase metabolism

Many health benefits have been described anecdotally. "Any anxiety, anything I'm struggling with, it's gone and when I come out of the water — I've left it in the water," says Audrey Nassal during a recent cold plunge in Seattle. Similarly, Riley Swortz, another cold plunger in Seattle, describes, "This calm washes over you and I feel like that lasts for at least a few days."

However, research on cold exposure, and specifically cold plunging, remains limited, and there is no clinical evidence that it actually provides people with health benefits. "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," Haman said.

According to Denis Blondin, a physiologist at the University of Sherbrooke in Canada, many of the hypotheses about cold plunging's health benefits are "plausible," but "there are no true randomized controlled trials where there is a large, representative sample size."

So far, most of the studies on cold exposure have been small, not well controlled, and largely focused on healthy young men, but researchers are currently working to change that. A team of researchers in the United Kingdom are planning the first large randomized controlled trial on using cold water swimming to treat anxiety and depression. It is set to launch next year and will enroll over 400 people.

"We're just starting to build some of that evidence" of the benefits of cold plunging, said Heather Massey, an environmental physiologist at the University of Portsmouth in the United Kingdom and part of the trial's research team.

How to cold plunge — safely

Although evidence on the health benefits of cold plunging is currently limited, Massey said she's "not trying to stop people doing it." Instead, she and other health experts offered advice on how to cold plunge safely.

Cold plunging "is not one size fits all," Haman said. "Every single individual needs to learn about their own body's response to cold and their limits," with the biggest determinant being body mass.

Cold plunging can also be hazardous, especially for people who are at risk of or diagnosed with a cardiovascular disease. "There are definitely medical conditions which would preclude cold water immersion," said John Kelly, a physiologist at the University of Chichester in the United Kingdom.

The cold shock from frigid water can also cause someone to pass out and drown, especially if they're not used to the cold, and chronic exposure can lead to "non-freezing cold injuries," Haman said. There's also a phenomenon known as "after drop" where your blood vessels dilate and the chilled blood from your extremities flow back to your core, which further reduces your temperature.

To prevent these potential issues, Haman recommends covering your hands and feet when you do a cold plunge and warming yourself up by moving around after you get out. And although there is a common misconception that staying in longer is better, you shouldn't stay in the water for too long.

"If somebody says 10 minutes in the cold is good, then we'll do 20 minutes because it's going to be twice as good," Haman said. "Physiology doesn't work that way."

Rather than focusing on the length of time you spend in the water, Haman and Massey say it's most critical to stay calm in the first few minutes, which are often the most painful. You also don't have to seek out the coldest temperature all the time either. According to Haman, he typically takes a chilly bath or shower in water that's roughly 70 degrees.

In general, people who are interested in cold plunging don't have to do anything complicated if they want to try it out. "I say not that long, so a few minutes, not that often, probably once a week, and not that cold," said Mark Harper, an anesthesiologist and author of the book Chill: The Cold Water Swim Cure. "And the other thing is — have fun." (Stone, "Shots," NPR, 10/8)

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