Water on the Stones

The Steam and the Hot Box

Mara: Katja Pettinen was about three. Her parents lived in a small Finnish town, in an apartment building with a sauna down in the basement. Every Saturday evening, each household had its own hour there. That basement is the first sauna she remembers, and she's written about it, and about the rest of her life with sauna, in Psyche.

Eli: A listener wrote in asking whether sitting in a sauna actually helps people live longer. Today's angle is the transformation of an ancient Finnish ritual of restoration into an overstated longevity prescription.

Mara: For Katja, that hour was simply Saturday. Now longevity advocates promote the same heat as a way to add years. Her life keeps running into the gap between those two: whether the heat does the work, or the unhurried life around the bench.

Eli: A weekly hour, set by the building. That's the original dose, if anyone's counting.

Mara: At twenty, she left Finland on an athletic scholarship. She trained for the heptathlon in the United States, stayed for a PhD in anthropology and settled in Canada. Through all those years, she wrote, 'my body craved the heat I had once known so intimately.' So she went looking. What she usually found was an electric heater with a sign beside it: don't throw water on the rocks. For a Finn, that strips out the löyly. In Finnish, löyly is what happens when water hits the hot stones.

Eli: So löyly is the steam itself, and the sign banned exactly that.

Mara: Exactly. In her tradition, there's no such thing as a 'dry sauna.' Her words on those rooms: 'That felt senseless to me: without the steam the room felt like a hot box.'

Eli: Author Bill Gifford used a gym sauna differently. A few years ago, during a particularly heavy winter, he kept ending up in his local gym's sauna. It became his refuge in a difficult season, quiet and solitary. One man, alone on a bench.

Mara: Katja's basement was the other version: a household at a time, the same Saturday hour every week. Heat, family and a fixed evening came as one ritual, long before anyone timed it for their heart. Which part of that package, if any, has to do with a long life is still open.

The Kuopio Numbers

Eli: The numbers that made sauna a longevity story come from eastern Finland, from the Kuopio Ischemic Heart Disease study. A team there analysed 2,315 men. The men had been followed for about two decades. The results came out in 2015. Men who used the sauna four to seven times a week were reported to have about a 40 percent lower risk of dying from any cause than men who went rarely.

Mara: And nearly half of the men studied had their own summer cottage.

Eli: Noted. For heart deaths, the gap looked wider. Dr. Michael Fredericson describes about a 50 percent lower chance of dying from a heart attack, another cardiovascular event or a stroke. What the study recorded was how often each man sat in the heat, and how he died.

Mara: Four to seven times a week is nearly every evening.

Eli: All of them men, aged 42 to 60 when they joined.

Mara: So the famous numbers belong to one region of Finland, and to men with saunas woven into their weeks, and often a cottage by a lake too. Eli has what the heat actually does inside a body.

A Workout for the Blood Vessels

Eli: Start with what the heat does to the blood. In a hot room, the body's answer is to push heat out through the skin. Normally only five to ten percent of what the heart pumps goes to the skin. In a sauna, that share climbs to 50 to 70 percent, about seven litres a minute. To supply that, cardiac output rises. That's the total volume of blood the heart moves each minute, which is a different thing from how fast it beats.

Mara: A heart working hard while its owner just sits there.

Eli: And faster too. Heart rate is reported to reach about 100 beats a minute, and up to 150 in intense sessions or for people new to it. A study found similar effects on physiological measures between traditional sauna, infrared sauna and moderate indoor cycling. Those were measures, not lifespans.

Mara: Dr. Peter Michalos calls it basically a way of exercising the blood vessels without having to actually go and exercise them.

Eli: It goes down to the cells as well. Heat sets off heat shock proteins, a protective response cells mount when heat stresses them. Dr. Rhonda Patrick suggests some of sauna's longevity benefits may come from that response. Those pathways are still being mapped.

Mara: Every one of those changes is measured on the bench, during a session.

Eli: And a racing heart on a hot bench is still a long way from a man alive two decades later.

The Edge of the Bench

Mara: Katja has treated this heat as ordinary since she was three. Finland's own records show what the same heat can do. The country counted 230 hyperthermia deaths, people whose bodies overheated. That was between 1970 and 1986. Most of them died in saunas, and most had been drinking shortly before. Alcohol can drop blood pressure low enough to make someone faint right there in the heat.

Eli: That's the skin blood flow from earlier, turned against people. With vessels wide open, blood pressure falls. Dr. Earric Lee calls fainting the main risk for healthy adults. Older people prone to it, and people on blood pressure medicine, are most exposed.

Mara: The heat also burns. The Helsinki Burn Centre treated 216 adults for contact burns from saunas. That was across thirteen years. More than a third of them needed an operation, and older age raised the risk. And for some people the heat is off the table. Safety reviews list contraindications, conditions that make an activity dangerous for a particular person. Unstable angina, a recent heart attack and severe aortic stenosis are on that list. Acute chest pain and a recent stroke get flagged too.

Eli: For unstable heart disease, that's not fine print. The advice is to stay off the bench or get medical advice first.

Mara: So the heat Katja grew up with can put people in hospital, and in Finland it's also linked to longer lives. Nobody has yet shown what the heat alone does over a lifetime. Whether the protection in those numbers comes from the heat or from something around it is now the sharper question, and Eli has the part where the numbers get tested.

The Cottage Confounder

Eli: Here's the snag built into Kuopio. The men chose how often to go. Nobody assigned them a schedule, as a randomized controlled trial would. In one of those, chance decides who gets the treatment, so the groups start out alike. Jonathan Jarry, at McGill, points out that without that, the study can't show cause and effect on its own. And these groups didn't start out alike: they differed in age, drinking, smoking and how active they were.

Mara: Any of those can be a confounding variable, an outside factor that makes the sauna look responsible for something it might not be doing.

Eli: The researchers did adjust for a long list: age, weight, blood pressure, cholesterol, smoking, alcohol, past heart attacks, exercise and socioeconomic status. The famous figures are what was left after that. They're hazard ratios, one group's rate of dying over the study set against another's. A ratio of one half means half the once-a-week men's rate. It's a relative gap, not half of all deaths.

Mara: Adjusting only catches what got measured. Critics have also proposed social class, and sick people avoiding the heat, as non-causal explanations.

Eli: And there was almost nobody to compare against. Professor Kevin McConway put it this way: 'Of the people studied, only 43 – that's about 2 per cent – said that they did not use saunas at all.' So Kuopio set frequent bathers against infrequent ones, never against people who skipped the heat.

Mara: Which is where the field splits. One reading, held by Dr. Earric Lee among others, is that the heat is an exercise-like stress that protects on its own. The other, held by Professor McConway among others, is that the same numbers show healthier, more leisured lives.

Eli: Then the trials came in. A 2025 meta-analysis, a study that combines data from multiple studies, pooled twenty randomized trials of passive heating. Systolic blood pressure fell by about two and a half points. Neither that nor the diastolic change was statistically significant. Reviewers of these trials concluded passive heating didn't improve any measured heart, metabolic or blood vessel marker, while warning the trials were small and possibly biased.

Mara: And no randomized trial has measured lifespan at all. A trial counting heart attacks or deaths, or a better-controlled replication outside Finland, could change that picture.

Eli: Think back to those summer cottages. In Finland, frequent sauna comes bundled with cottages, rest and leisure, and from the outside it's hard to tell the heat's share from the life's.

Finding the Way Home

Mara: In the summer after she turned fifty, Katja went back. Career burnout and the end of a long-term relationship had left her needing, in her word, to recalibrate. She rented a small cottage by a lake in southern Finland and moved in with her dog for nearly four months. Each evening she lit the wood-fired sauna, stepped into the heat, then into the lake, then back to the warmth. She said those cycles helped her sort through anxiety. It was her first full season in Finland in more than thirty years.

Eli: A wood fire and a cold lake. Everything the hot box with the sign left out.

Mara: And the researchers behind the Finnish studies stress that the Finnish sauna is, by its very nature, designed to reduce stress.

Eli: Stress relief is a different job from a workout, though. In a sauna, the heart is under hemodynamic stress, the push of blood flow and pressure on the heart and vessels. But one review spells out the difference: it's pumping to shed heat, not to feed working muscles, and the adaptations differ.

Mara: Which is why Dr. Earric Lee tested the two together. In an eight-week trial, he reported, people who added sauna to regular exercise improved their cardiovascular condition more than those who only exercised, with bigger falls in systolic blood pressure and total cholesterol.

Eli: And the heat-only trials have their own limits. They were small, and researchers want bigger, longer, standardized ones. Dr. Prashant Rao suggests they may simply not have lasted long enough to catch benefits that take years, or a lifetime.

Mara: So, the listener's question. On the evidence so far, sitting in a sauna hasn't been shown to make anyone live longer on its own. The Finnish bathers' lower death rates came with cottages, leisure and better health to begin with, and the heat alone hasn't held up in trials. The Longevity Report Card's advice is that for people who enjoy it and are otherwise well, keeping going looks safe, just without counting on extra years.

Eli: Dr. Lee puts the heat in its place: 'To maintain strong cardiovascular health over time, it's important to adopt the lifestyle behaviors of engaging in regular cardiovascular exercise, eating a low-fat diet, and managing stress effectively.'

Mara: That three-year-old in the basement had the whole thing at once: a Saturday hour, her household, the heat. At the lake, Katja found it again and decided to move back to Finland. She wrote that 'by relocating what sauna wrote into my body long ago, I found my way home.'

Eli: Three signals to watch. Whether a long trial ever shows regular heat itself cutting deaths. Whether the Finnish link holds up in racially diverse populations outside Finland.

Mara: And whether hidden heart disease keeps frailer people out of the sauna, so that the men who went less were sicker from the start.

Eli: One piece to explore is heat shock proteins.

Mara: And keep following health with us.

Eli: Thanks for listening. I'm Eli.

Mara: And I'm Mara. Until next time.