Sauna scientists Dr. Hans Hägglund (left to right), Earric Lee and Ashley Mason take a steam bath in the Japanese sauna at The Well in Oslo, Norway. They are part of a group of international researchers studying the potential health benefits of sauna and other thermal therapies.
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Scientists have long marveled at how the human body tolerates extreme heat and what that means for our health.
In the late 1700s, British scientists made a bold move experiences on thermoregulation, subjecting themselves (and a dog) to a very hot room and observing that – unlike the steak and eggs that accompanied them – their own bodies did not cook.
The acute physiological response to heat is now well understood.
When faced with extreme temperatures, our blood vessels dilate, heart rate increases, and blood is pushed to the skin where it cools as we sweat. Our body releases hormones and activates heat shock proteins that protect our cells.
This understanding of our physiology has shaped medical care, for example for heat-related illnesses. However, the other side of the equation – the potential therapeutic benefits of heat exposure – has received far less attention from modern medical science.
Meanwhile, centuries-old practices, like the sauna, based on stressing the body with heat, are enjoying new popularity.
From sauna socials to the broader wellness and optimization movement, the level of public interest has surprised even longtime enthusiasts like Dr. Hans Hägglundhematologist and stem cell researcher at Karolinska University Hospital in Stockholm.
Sanna Bendiksen Landhaug (left) and Ida Hellum Reppen take an early morning sauna at Sukkerbiten in Oslo, Norway. Sukkerbiten is the Oslo Sauna Association’s group of many small saunas of varying styles, lined up along a pier.
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“It’s really booming,” says Hägglund, double the “sauna doctor” in his home country thanks to a popular book he wrote on the subject. “Unfortunately, there isn’t much evidence yet.”
At least, not of the caliber of studies that Hägglund and other scientists can point to if they want medical societies and government agencies to consider sauna and other forms of heat therapy as a bona fide intervention — a lifestyle approach that can be recommended to prevent and treat chronic health problems.
But Hägglund and a small group of international scientists are pushing to make it happen – and organizing what is a niche and disparate area of research.
Bringing science to the sauna
In late September, about 15 of them gathered for the first time at the International Thermal Therapy Research Symposium to figure out how to rigorously study thermal therapy — a bucket that includes a Finnish sauna, infrared, hot water immersion and more — and to form an organizing scientific body that will help advance the field.
Sauna scientists Ashley Mason (left to right), Earric Lee and Dr. Hans Hägglund are among international scientists gathered for the International Thermotherapy Research Symposium in September at the Well in Oslo, Norway.
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The two-day gathering was held at a trendy resort outside Oslo, Norway, called The Well, where nude bathing is the norm and essential oil-infused rituals, based on traditions like German Aufgusstake place throughout the day. This took place the day before International Sauna Congressan event that attracts hundreds of sauna enthusiasts and experts every four years.
Some conference organizers, such as Ashley Masonclinical psychologist at the University of California, San Francisco, acknowledges that part of his goal is to dispel the stench of wellness hype.
“We want to present this as a real area of research, not as something fringe or woo-woo,” says Mason, an associate professor of psychiatry and behavioral sciences who is currently do tests on heat therapy for depression, sleep and other aspects of mental health.
While the sauna has been studied off and on for decades, very little of this research has come from well-controlled human trials. And it is often difficult to draw definitive conclusions from existing evidence; studies are small, methods vary widely, and key measures are sometimes missing.
“We’re everywhere,” Mason says. “If we want to be taken seriously, we need to have consistent terms, so people understand how to refer to and talk about our work.”
The nuances of measuring ambient humidity and body temperature, or how best to define heat therapy, may be afterthoughts for the average sauna user, but these are all extremely important when bringing together data from different countries and institutions.
Earric Lee, a postdoctoral researcher of the Montreal Heart Institute, which is leading the initiative, says scientists must first agree on standards. It’s a careful process involving dozens of other experts that will ultimately set the stage for the kind of larger, multisite trials that can answer some fundamental questions for scientists and the public.
What are the real benefits? How often should you go? What are the risks? How hot does it need to be?
“People want information. I know ‘listening to your body’ isn’t enough,” Lee says, “but I really can’t give you any recommendations, and that’s the truth.”
Early evidence suggests benefits of sauna exposure
There is certainly reason to believe that heat – provided as a powerful stimulus within a limited time frame – keeps the promise for health.
“Passive thermal therapy”, as it is called in the scientific literature, works the cardiovascular system in a manner similar to light physical activity and provides some of the same benefits, such as improvements in blood pressure, arterial stiffness, and vascular health.
Some experiments also indicate improvement in markers of inflammation, although here, as in many areas, the results are inconclusive, Lee says.
There is particular interest in how heat can help people with cardiovascular and metabolic problems, as well as the elderly, says Shepherd Antprofessor of clinical environmental physiology at the University of Portsmouth in the United Kingdom
For example, his laboratory showed spend time in a hot tub improved resting metabolic rate and some measures of insulin sensitivity for people with type 2 diabetes.
“Exercise is king, exercise is medicine, but for those who can’t do it easily, can we get the same effects?” he asks. “Looks like we can do it.”
In one of the only In randomized controlled trials of sauna, Lee found that adding it to an exercise program conferred additional benefits for people at risk of cardiovascular disease. He is currently conducting a trial on cardiac rehabilitation patients.
Furthermore, several research groups are studying whether heat can help treat depressionbuilding on a landmark study that showed a significant decrease in symptoms after a session in a special infrared machine.
“We have many, many lovely little studies,” says Shepherd. “Governments are not going to listen until we give them the randomized controlled trials.”
Sauna Research Grows
The recent rise in scientific interest comes largely from a series of observational studies carried out in Finland.
The first — published a little over ten years ago — shown using sauna four to seven times a week was associated with a 40 to 60 percent lower risk of cardiovascular disease and death, compared to those who only went once a week.
“It was a strong signal and impetus for a lot of labs to stand up and say, ‘Hey, there might be something here,’” says Lee, who earned his Ph.D. in collaboration with the research leader of the University of Eastern Finland group, Dr Jari Laukkanen.
Sauna scientists Ashley Mason (right) and Dr Hans Hägglund towel off after a session in the Japanese sauna at The Well, Oslo, Norway.
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Siv Dolmen for NPR
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