Mickey Smith let out a scream as she adjusted to the freezing water. It was her first time competing as a member of the Puget Sound Diving Team in Seattle, Washington. Photo by Mike Kane for NPR, hide caption
Mickey Smith couldn’t help but exclaim as she adjusted to the cold water. It was her first time diving with the Puget Sound Dive Team in Seattle, Washington.
When you jump into icy water, your body’s first reaction is a “cold shock” reaction. Your heart rate will increase. The release of stress hormones will increase dramatically. You will suddenly start to gasp for air and may even begin to breathe faster.
If you hold out long enough and get through those first painful moments, what will be your reward? You will start shaking.
To the uninitiated, it may be unclear why the cold infusion method has attracted so many followers in recent years.
But those who enjoy cold baths—whether in an icy lake, the ocean, or a backyard ice bath—often describe the powerful, even transformative impact they have on their mental state and sense of well-being.
“Any anxiety, any emotion that I was struggling with just went away, and when I got out of the water, I left everything in the water,” Audrey Nassar said during a recent Sunday morning dive at a Seattle beach. It was one of several meetups organized by the Puget Sound Plungers, a group of thousands of members who regularly dive into the frigid waters of the Pacific Northwest.
Riley Schwartz, who was swimming next to Nassar, said she loved the moment her body stopped shaking from the shock. “At some point, you don’t feel the cold anymore,” she said. “This calmness comes over you, and I think it lasts for at least a few days.”
Rain or shine, cold-water swimmers gather in front of the pool at Seattle’s Golden Gardens Park before 8 a.m. every Sunday. The plunge is a group event, and each person decides how long they want to stay. Mike Kane for NPR hide caption
Rain or shine, cold shower participants gather in front of the pool at Seattle’s Golden Gardens Park before 8 a.m. on Sunday. The plunge is a group event, and everyone decides how long to stay in the water.
The huge popularity of the trend – social media is filled with photos of half-frozen torsos, and some enthusiasts spend thousands of dollars on expensive cold-water baths – has in turn fueled demand for rigorous scientific evidence.
“I never thought it would go this way,” said Francois Harman, who has studied the effects of cold for more than two decades. “We still have a lot of work to do.”
When Harman, a professor at the University of Ottawa, first began his work in the field, he found himself in a discipline where talent was rare. Research focused on the risks of cold exposure, combat, and survival in harsh climates, while potential therapeutic benefits were rarely considered.
The widespread attention makes Harman optimistic that science will shed more light on how cold can improve health in the coming years. But he cautioned that much of the information currently available is based on “very weak research,” and some popular ideas go far beyond what we actually know.
“Many people make claims and blindly believe that are either completely unfounded or based on just a few newspapers and social media,” he said.
So does cold-water immersion, or “ice baths” as some call them, actually have any health benefits? “We’re just starting to gather some of the evidence,” says Heather Massey, an environmental physiologist at the University of Portsmouth in the UK and an avid cold-water swimmer.
We asked Harman, Massey, and other scientists studying the effects of cold to break down some of the health claims and tell us which ones have the strongest evidence, which are less convincing, and which hypotheses show promise based on new research.
In a place like Seattle, courage begins on the beach, in the fresh air. From left: Elizabeth Eddy, Vivian Sharples, Patti Stevenson, and Alena Ishchenko. Mike Kane for NPR hide caption
In a place like Seattle, the test of courage begins on the beach, in the fresh air. From left to right: Elizabeth Eddy, Vivian Sharples, Patti Stevenson, and Alena Ishchenko.
Just as the effects of exercise vary (jogging is different from lifting weights), the effects of cold vary. It depends on the type, duration, intensity, etc. of exposure. This makes it difficult to draw firm conclusions from the evidence base, as the study methods vary widely.
Scientists do know one thing: Cold is one of the most powerful natural stressors, which means “our physiological response is always going to be very strong,” Harman says.
Especially when you add water, which absorbs body heat faster than air. While there is no universal definition of cold water swimming or diving, water temperatures are typically 60 degrees Fahrenheit (about 15 degrees Celsius) and below. (For example, in Seattle’s Puget Sound, water temperatures range from 40 to 50 degrees Fahrenheit.)
Unsurprisingly, its health risks are better documented in the scientific literature than its potential benefits (including the risk of cardiac arrest, drowning, and hypothermia). Potential benefits of cold water often involve metabolism, the immune system, inflammation, and mental health.
Denis Blondin, a physiologist at the University of Sherbrooke in Quebec, Canada, says many of the assumptions made here are “reasonable.” But “there are no real randomized controlled trials, studies with large representative samples,” he says. Instead, most studies of the effects of cold are small, poorly controlled, and tend to include only healthy young men.
Within minutes of the dive, the group dive felt more like a Sunday brunch, with everyone chatting and laughing, than a harrowing adventure. Photo by Mike Kane for NPR, hide caption
After a few minutes in the water, the group dive became more like a Sunday breakfast, full of conversation and laughter, than a torturous ordeal.
So what should cold water lovers do? Here is a review of some common claims.
Many studies support the fact that acute and repeated exposure to cold can improve insulin sensitivity, which helps control blood sugar levels.
“You’re activating your muscles through shaking, which causes a very similar response to what you see during exercise,” Harman said.
Blondin said these changes could persist for 24 to 48 hours after cold weather, although it’s unclear how such changes would play out in long-term studies.
“The improvement in insulin sensitivity was even greater than the improvements seen with exercise, which is a little surprising,” he said.
In this sense, the cold itself is a form of exercise. It can even increase your metabolic rate by five times compared to resting levels. The effectiveness of cold exposure for weight loss has not been proven, but some small studies have shown that it may help treat type 2 diabetes.
It was Courtney Burkett-Jackson’s first dive with the Puget Sound Dive Team. “I was really surprised at how calm and relaxed I felt,” she said. Mike Kane for NPR hide caption
It was Courtney Burkett-Jackson’s first time diving with the Puget Sound Dive Team. “I was really surprised at how calm and relaxed I felt,” she said.
With the exception of a few studies of cold-water swimmers, metabolic studies have exposed people to cold air for long periods of time or worn special cooling suits, as in Blondin’s lab, at temperatures that did not feel as extreme as immersion in ice water.
“A lot of people would like to draw conclusions from our data and make conclusions about cold water swimming, but that’s not the case,” Blondin said.
In cold-weather circles, you’ve probably heard that regularly taking a dip in ice water can prevent illness. It may help boost the immune system, but Harman said the evidence for that claim remains “completely unclear.”
Some studies have shown changes in white blood cells (others have not), suggesting that the immune system may be better able to respond to infection. However, because the studies typically measure biomarkers rather than actual disease, their practical significance remains uncertain.
The studies mostly involved experienced cold-water swimmers, so they were unable to distinguish between the effects of exercise and cold. Overall, the small sample sizes and broad scope of the protocols led to “mixed results,” according to a review of the evidence.
Some bathe for just a few minutes, while others stay longer, enjoying the numb feeling of their skin. Photo by Mike Kane for NPR, hide caption
Some people take a bath for just a few minutes, while others stay in it longer, enjoying the numb feeling of their skin.
One promising study based on real-world data comes from the Netherlands, where researchers conducted a large randomized controlled trial. Subjects took a hot shower followed by a cold shower for 30, 60, or 90 seconds. Participants who regularly took cold showers saw a 29% reduction in sick leave, but the actual number of sick days did not decrease.
However, the study relied on self-reported data from the participants, who were generally healthier than the general population. Other studies suggesting that cold-water swimming can help prevent respiratory infections also tend to rely on self-reporting, making the results seem contrived.
Another thing to consider: If you spend too much time in the water, you risk “getting hypothermia and weakening your immune system,” Harman said. “It all depends on how cold we mean.”
One popular claim is that cold water can curb chronic inflammation associated with many diseases, from autoimmune diseases to diabetes.
Mark Harper, an anesthesiologist and author of Cold: Cold Water Float Therapy, says there are certainly biological reasons for this, as well as some anecdotal evidence.
A few years ago, Harper’s team surveyed about 700 outdoor swimmers to learn about the health effects of swimming.
“About a quarter of patients use it for conditions like fibromyalgia, arthritis, inflammatory bowel disease, all of which involve inflammation,” he said, “so we assume it works.”
Alexis Gentry started trying out the Cold Spring sprint this summer and hasn’t been able to put it down yet. What does she get out of it? “Feeling the warmth in your body, feeling the cold, but being able to embrace it,” she said. “It’s nice to see so many people doing it.” Mike Kane for NPR hide caption
Alexis Gentry took up cold-water diving this summer, and it didn’t stop her. What did she get out of it? “It was really nice to see so many people doing it.”