How the body handles extreme heat

When exposed to extreme temperatures, blood vessels dilate, heart rate speeds up and blood moves to the skin where it cools through sweat. The body releases hormones and activates heat shock proteins that protect cells.

Sauna's popularity outpaces the science

Sauna and heat therapy are booming in popularity, from social meetups to the broader wellness movement.But Dr.Hans Hägglund, a hematologist at Karolinska University Hospital in Stockholm, says there is still not very much evidence.

“It's really booming. Unfortunately, there is still not very much evidence out there.”

Scientists need rigorous proof

Hägglund and other researchers want medical societies and government agencies to view sauna as a bonafide intervention for preventing and treating chronic health conditions. But that requires the caliber of studies currently lacking.

First international symposium convenes

In late September, about fifteen international scientists gathered for the first International Heat Therapy Research Symposium at The Well outside Oslo, Norway, to establish how to rigorously study heat therapy and form an organizing scientific…

Moving beyond wellness hype

Ashley Mason, a clinical psychologist at the University of California, San Francisco, says the goal is to introduce heat therapy as an actual field of research, not something fringy or woo-woo.

“We want to introduce this as an actual field of research, not something fringy, or woo-woo.”

The problem with existing research

Very little sauna research comes from well-controlled human trials. Studies are small, methods vary significantly and key measurements are sometimes missing. It is hard to draw firm conclusions from what evidence does exist.

Standardizing the science

Earric Lee, a postdoctoral researcher at the Montreal Heart Institute, says scientists first need to agree on standards.

The questions that need answers

Scientists need to establish what the actual benefits are, how often people need to use sauna, what the risks are and just how hot it needs to be.

“People want information. I know 'listen to your body' doesn't cut it, but I really can't give you recommendations, and that's the honest truth of it.”

Heat works like light exercise

Passive heat therapy works the cardiovascular system in ways similar to light physical activity and delivers some of the same benefits, such as improvements in blood pressure, arterial stiffness and vascular health.

Benefits for those who cannot exercise

Ant Shepherd, a professor of clinical environmental physiology at the University of Portsmouth in the U.K., notes that heat therapy could help people with cardiovascular and metabolic conditions and the elderly.

“Exercise is king, exercise is medicine, but for those who can't do that easily, can we get some of the same effects? It looks like we can.”

Finnish studies sparked scientific interest

The uptick in recent scientific interest largely stems from observational studies done in Finland. One published just over a decade ago showed using sauna four to seven times per week was associated with a forty…

Other promising findings from research

Subsequent Finnish studies suggested other benefits, like lower rates of Alzheimer's, respiratory disease and lower markers of chronic inflammation.Long-running studies from Japan have also linked regular hot tub use with lower risk of cardiovascular disease.

Observational data has limits

While promising, experts stress you can only extrapolate so much from observational data because it relies on self-reports and results can be skewed by other factors.

“The effects are quite large, so we're fairly optimistic, but that's about as far we can go as scientists.”

Funding challenges ahead

In countries where heat practices are deeply interwoven into society, such as Finland and Japan, public funding has supported some research.In the U.S., the National Institutes of Health is funding Mason's work.

Replicating findings globally

Dr.Jari Laukkanen, who led influential sauna research in Finland, welcomes efforts to organize the field and replicate findings in other parts of the world.

“They are really demanding. Pharmaceutical companies are doing this kind of study, but they have the resources. We don't have those yet.”