Cold plunges are all the rage. But what does the science say?

Hundreds of Canadians rang in the new year by jumping into near-freezing bodies of water on Monday.

The New Year’s Day cold plunge, or Polar Bear Dip, is an annual tradition more than a century old — a social event of perhaps limited appeal that unites shivering strangers in joyful discomfort.

But the cold plunge has entered the mainstream in recent years, along with lofty claims about its supposed health benefits, from reducing inflammation and boosting immunity to alleviating depression and anxiety.

Influencers are taking ice baths all over TikTok, and the practice has been touted by celebrities including Drake, Justin Bieber and Joe Rogan. Cold plunge tubs are being sold for hundreds or thousands of dollars to people who want to make it part of their daily routine.

But is there any science behind these supposed benefits? Or is this just a lot of hype?

“People come out and they usually feel just fantastic,” said John Holash, assistant professor with the faculty of kinesiology’s Human Performance Lab at the University of Calgary.

Vancouverites dive into the new year with Polar Bear Swim

Following a tradition that’s now more than a century old, brave swimmers flooded a Vancouver beach to ring in the new year with a chilly plunge at the annual Polar Bear Swim.

And yet, “when you jump into that really, really cold water, it’s a real insult to your body, and your body perceives it as a threat.’

Holash says there’s little science to conclusively support some of the purported health benefits of cold plunges, in part because it’s difficult to find consistent responses across large groups of people, given many factors that change how our bodies respond.

Most people who do cold plunges tend to be in fairly good shape, he says, which creates a “healthy user bias.”

However, there is some evidence of short-term mental health benefits. Studies of cold water exposure have found huge spikes in participants’ levels of the noraderenaline and dopamine. Both are hormones and neurotransmitters that are associated with, respectively, alertness and pleasure, among other positive conditions.

A cold plunge “increases your blood circulation, it pumps up your heart rate [and] you have a change in a lot of circulating hormones within the body,” Holash said.

While scrolling social media might give you “a small hit” of dopamine that lasts five to ten minutes, “these changes that we see in hormone profiles [from a cold plunge] tend to last for hours. So they tend to be really really robust and long-term changes.”

Would you go for a swim in this freezing river? Polar plungers claim it’s a positive experience

These die-hard swimmers in Calgary’s icy Bow River claim cold plunges invigorate them.

Holash says though the practice is trendy now, it goes back thousands of years. The ancient Greeks used cold water therapy for depression.

“Some of the results might be anecdotal, but when you get anecdotal evidence that kind of spans 3,000 years you might be onto something, even though it might be hard to prove in a lab.”

Holash says other purported benefits, like increased metabolism, might come over time with repeated cold water exposure due to an increase in brown adipose tissue, also known as brown fat, which helps the body regulate temperature and burn calories.

But Stephen Cheung, kinesiology professor and senior research fellow at Brock University, in St. Catharines, Ont., says he’s skeptical of the long-term physical benefits.

He says some athletes will take cold baths after training or competition to reduce inflammation and swelling from significant muscle damage, but there’s no solid scientific evidence to show more sedentary people will get the same benefits.

“Absolutely I think cold baths can improve your mood, but I don’t think they have these other long-term kind of physiological health benefits,” Cheung said.

Both experts agree that cold plunges are not for everyone, and in fact can be dangerous for some.

They say anyone with cardiovascular issues, such as poor circulation, for example, should seek medical advice before doing a cold plunge, because it will increase one’s heart rate and blood pressure, while also making blood vessels shrink and muscles constrict.

“If you’re sedentary and you’re prone to having heart issues, that’s a double whammy of risk factors because you’re not used to having your heart work so hard, so quickly,” Cheung said.

Holash says it is also important to remember cold plunges are not an endurance event. He said two to three minutes is a good amount of time to maximize the potential benefits, and that staying too long beyond can increase the risk of hypothermia.

“Prolonged exposure to the cold, your hands and feet are going to start feeling really rubbery, they’re going to feel disconnected. You’re going to lose some of that fine motor co-ordination. And you don’t want to lose the control over your body when you’re trying to get out, or twist an ankle on a cold, slippery rock,” he said.

Taking a cold plunge in Kitchener, Ont.

A group of people are trying a cold barrel tub for the first time at KW Sauna in Kitchener, Ont. The water in the tub is 8 C and beginners, like those in the tub, are encouraged to stay in for two and a half minutes at a time.

Both stress the importance of doing a cold plunge with other people, especially if it’s in a large body of water.

As for the fancy backyard tubs shown off by celebs and influencers, Holash and Cheung say a person can achieve the same effect by simply running a cold bath or shower at home. Cheung says as long as you don’t have any existing health concerns, there is no evidence that doing so will cause any harm.

“If you want to kick the coffee habit and go and do a cold shower in the morning instead to wake you up, go ahead,” he said.