Knowledge base · Research
Four saunas a week, or one. That gap turned out to be wide.
Between 1984 and 1989, researchers in Kuopio, eastern Finland, recorded how often 2,315 men used the sauna. They then followed them for more than twenty years. Here is what they found, and what it does and does not mean.
The study
Who was followed, and for how long
2,315 men in eastern Finland, followed for over twenty years.
The best known sauna study in the world comes from Kuopio in eastern Finland. Researchers at the university there recorded how often 2,315 middle-aged men used the sauna, then followed them for a median of more than twenty years.
The men were between 42 and 60 years old at the start. The researchers recorded who died during those twenty years and of what. They then adjusted their calculation for everything that could distort the picture: age, smoking, alcohol, cholesterol, blood pressure, diabetes, weight, fitness and socio-economic position. What remained was published in JAMA Internal Medicine in 2015.
One thing is worth knowing up front, because summaries tend to leave it out. The frequent sauna users were not compared with people who never set foot in one. In Finland, almost everyone goes at least once a week. So the comparison runs from once a week to four to seven times a week.
The findings
What stood on paper after twenty years
Four to seven times a week, set against once a week.
The men who went four to seven times a week came out better on every measured point than the men who went once a week. Below are the differences in risk as the researchers published them, from the model adjusted for the factors listed above.
Sudden cardiac death
63% lower risk
This is the figure the study became known for. Note the scale behind it: the group going four to seven times a week numbered 201 men, and ten cases occurred within it. JAMA Internal Medicine, 2015.
Cardiovascular disease
50% lower risk
For deaths from cardiovascular disease as a whole, the difference was exactly half. That figure rests on more cases than the previous one, which makes it firmer. Same publication, same groups.
All causes of death
40% lower mortality, later 14%
Looking not at the heart but at all causes of death together, the 2015 paper reported a difference of forty per cent. It shrank when the same researchers looked longer: 2,575 men from the same cohort, followed for almost 28 years, 1,618 deaths. Those going three to seven times a week then had a 14 per cent lower mortality than those going at most twice. JAMA Internal Medicine, 2015 and Experimental Gerontology, 2022.
High blood pressure
46% lower risk
Of 1,621 men with normal blood pressure at the start, the frequent sauna users developed high blood pressure less often over almost 25 years. American Journal of Hypertension, 2017.
From the same cohort
It did not stop at the heart
Dementia, stroke, and later a cohort that included women.
The same Kuopio data produced more. Age and Ageing published an analysis of dementia in 2017: among the men going four to seven times a week, the risk was 66 per cent lower than among those going once a week. Here too, the numbers in the top group are small, and that figure is now less settled than it looks.
An independent and far larger Finnish cohort came out lower: 13,994 men and women aged 30 to 69, followed for 39 years, published in Preventive Medicine Reports in 2020. Those going nine to twelve times a month had a 19 per cent lower risk of dementia over that whole period than those going at most four times a month. Going more often still brought no demonstrable further gain, and in the first twenty years the association was far stronger than over the full span. So there is an association, but nobody knows precisely how large it is.
The main limitation of the 2015 study was that it covered men only. The authors wrote themselves that it needed repeating in women, and that has happened. In 2018 the same research group published a cohort in BMC Medicine of 1,688 Finns averaging 63 years of age, more than half of them women. There too, deaths from cardiovascular disease were lower among those going four to seven times a week, and Neurology carried a comparable picture for stroke that year.
Session length
How long you stay mattered too
Longer than nineteen minutes fared better than shorter than eleven.
The researchers also looked at how long each session lasted. Those who stayed longer than nineteen minutes had a lower risk of sudden cardiac death and of death from cardiovascular disease than those who stayed under eleven minutes. For the sessions in between, they found no clear difference.
Two caveats on duration
For total mortality, meaning all causes of death together, session length showed no link with risk at all. That association held only for the cardiovascular outcomes.
Staying longer is not automatically better either. The saunas in this study averaged 79 degrees Celsius. The researchers stress that their findings do not transfer readily to steam rooms or hot tubs, which run at far lower temperatures.
Why the heart responds
In the heat your heart does something familiar
The heart rate climbs to the level of light to moderate exercise.
Sitting still in a hot room sounds passive, but your body is working hard to stay cool. The blood vessels in the skin open wide, blood is sent to the surface to shed heat, and the heart pumps faster to move it around. In the JAMA article the researchers write that the heart rate can rise to a hundred beats per minute during a gentle session, and to a hundred and fifty in a hotter one. That corresponds, they say, to light to moderate physical exercise.
What happens just afterwards was studied separately in 102 Finnish participants and published in the Journal of Human Hypertension in 2018. After a single thirty-minute session, systolic pressure fell on average from 137 to 130 and diastolic from 82 to 75. Arterial stiffness also decreased in that measurement. This is one experiment with 102 people, which the researchers have published in several journals, and a short-lived effect after one session, not a treatment.
Sauna and exercise
The association holds alongside exercise, not instead of it
The most important finding from Kuopio concerns the combination.
For 2,291 of these men fitness had also been measured, with a maximal exercise test. In Progress in Cardiovascular Diseases, 2018, the researchers set fitness and sauna use side by side, over a median of 26 years and 226 cases of sudden cardiac death. With good fitness plus frequent sauna, three times a week or more, the risk was lowest: 69 per cent lower than with low fitness plus infrequent sauna; with good fitness alone it was 51 per cent lower. Frequent sauna with low fitness produced no difference that held up statistically.
A randomised trial found the same from the other side. In the American Journal of Physiology, 2022, 47 people with low activity levels, averaging 49 years of age, followed an exercise programme for eight weeks, one group with fifteen minutes of sauna after each session, the other without, alongside a control group that changed nothing. Exercise alone improved fitness by 6.2 millilitres of oxygen per kilogram of body weight per minute. The sauna after training added another 2.7 to that, and a systolic pressure 8 mmHg lower than with exercise alone.
What this means for you
If you hope to trade a gym membership for a sauna, we have to disappoint you: the research gives no grounds for that. If you already exercise, both studies show the combination coming out best.
A sauna in the garden is the practical form of that. You train wherever you like, and the quarter of an hour afterwards starts at your own back door.
The small print
What this research does not say
Four questions worth asking of any health statistic.
This is observational research. It shows what occurs together, not what causes what. The researchers are the clearest about that themselves, and those caveats belong here just as much as the percentages do.
Compared with whom, exactly?
With Finns who go once a week, not with people who never go. Weekly sauna use is the norm there. There is a question of scale as well: the top group numbered 201 men and ten cases of sudden cardiac death. With numbers like that the margin around a percentage is wide, and the true effect could be considerably smaller or larger.
Does this prove the sauna protects your heart?
No. People who use the sauna often turn out to fare better, which is not the same as the sauna making the difference. The researchers adjusted for fitness, smoking, alcohol and a range of other factors, but write themselves that influences they did not measure may remain. They also point out that it could work the other way round: someone already ill may go less often.
Did it hold for women too?
The 2015 study covered men only. It has since been supplemented by a cohort of 1,688 Finns, more than half of them women, published in BMC Medicine in 2018, with a result pointing the same way. All the major studies on this do come from the same Finnish research programme. Independent replication elsewhere is still missing.
Does this apply to every sauna?
According to the researchers, no. Their measurements concern the Finnish sauna at an average of 79 degrees Celsius, where water goes on the stones. For steam rooms, hot tubs and other types running at lower temperatures, the findings do not simply carry over. An infrared cabin works on an entirely different principle and falls outside this research.
What you can do with it
From Kuopio to your own garden
Four things the research itself points to.
We give no health advice. Your doctor is the person for that. What we can do is write down what the research actually measured, so you can see for yourself what a sauna at home asks of you in practice.
- Regularity is what the research is about. What was measured is a pattern over years, not one remarkable session. A sauna twenty metres from your back door sustains that pattern more easily than an outing you have to travel for.
- Count on fifteen to twenty minutes a time. In the Finnish measurements, sessions above nineteen minutes fared better on the cardiovascular outcomes than those under eleven.
- The saunas studied sat at around 79 degrees Celsius. That is an ordinary Finnish sauna, with water on the stones. If you want to stay close to what was actually researched, that is the type to look at.
- Put water ready before you start. In the same Finnish measurements, a sauna user lost half a litre of fluid per session on average. You drink that back afterwards.
Safety
When to call your doctor first
Heart conditions, pregnancy or doubt: talk it through first.
A sauna is warm work for your heart, which is precisely why some people should discuss it first. If you have a heart condition or unstable blood pressure, or if you are pregnant, put the question to your doctor or specialist before you begin. The same applies if you take medication that affects your blood pressure or fluid balance.
A few plain rules apply to everyone. Do not drink alcohol before or during sauna use. Come out as soon as you feel light-headed, and stand up gradually rather than all at once. Drink water afterwards. Never leave children in a sauna on their own.
Further reading
Three articles alongside this cohort
Is a hot tub good for your heart?
The Japanese bathing cohort: nineteen years of follow-up, with warm bathing rather than sauna. The same kind of research, with different caveats.
What a sauna does not do
Seven claims about calories, detox and cortisol checked against what has and has not been demonstrated.
Infrared sauna or Finnish sauna: what is the difference?
Why the Finnish research does not simply transfer to an infrared cabin, and which differences in temperature and use sit underneath that.
Accountability
Sources and author
Every figure on this page was checked against the original publication.
See for yourself
From research to a sauna that suits you.
We make no health promises. What we can do is show you how a Finnish sauna feels from the inside and how an infrared cabin differs from it. In our showroom in ’s-Graveland they stand side by side across two floors. The infrared cabins are switched on; the Finnish saunas stand dry.