Sauna benefits: what the Finnish studies actually found

Sauna benefits are real enough to take seriously and less proven than the headlines suggest. The best-known evidence, a 2015 JAMA Internal Medicine study of 2,315 Finnish men followed for about two decades, found that men who used a sauna 4 to 7 times a week had roughly half the rate of fatal cardiovascular disease of men who went once a week. That study is observational: it shows a strong association, not proof that the sauna itself did the work.

That distinction matters if you are deciding whether a home sauna belongs in the plan, or whether the 20 minutes would be better spent on a walk or an earlier bedtime. Here is what the Finnish research found, how solid it is, and how to use heat sensibly.

What did the Finnish sauna study actually find?

The study that launched a thousand podcast segments came from a long-running cohort study in Eastern Finland. Researchers enrolled men aged 42 to 60 between 1984 and 1989, recorded their sauna habits, and then followed them. The median follow-up was 20.7 years. Over that time the cohort recorded 190 sudden cardiac deaths, 281 deaths from coronary heart disease, 407 deaths from cardiovascular disease and 929 deaths from all causes.

The paper, published in JAMA Internal Medicine in 2015 by Laukkanen and colleagues, split the men into three groups: once a week (601 men), 2 to 3 times a week (1,513 men) and 4 to 7 times a week (201 men). Note the shape of that distribution. In Finland, a weekly sauna is the floor, not a lifestyle choice. The comparison is between normal Finnish use and heavy Finnish use.

After adjusting for known cardiovascular risk factors, the more frequent groups had lower risk on every fatal outcome the researchers measured. The pattern was graded: 2 to 3 sessions looked better than one, and 4 to 7 looked better again.

A hazard ratio of 0.50 for fatal cardiovascular disease in the 4-to-7 group means those men died of cardiovascular causes at about half the rate of once-a-week users over the study period. Session length showed a similar pattern. Men whose sessions ran more than 19 minutes had a hazard ratio of 0.48 for sudden cardiac death compared with sessions under 11 minutes.

Why the heart result is plausible

There is a reasonable physiological story behind the numbers. According to Harvard Health Publishing, skin temperature "soars to about 104° F within minutes" in a sauna, and "the pulse rate jumps by 30% or more, allowing the heart to nearly double the amount of blood it pumps each minute." Most of that extra blood flow goes to the skin.

Put simply, you are sitting still while your cardiovascular system does something that resembles light to moderate exercise. The University of Eastern Finland, summarizing later work from the same research group, describes sauna use as triggering "an increase in heart rate equal to that seen in low to moderate intensity physical exercise" and notes that it is associated with lower blood pressure. Repeated regularly, that kind of stress on blood vessels could plausibly improve their function over time.

Plausible is the operative word. A mechanism that fits the data is not the same as data that proves the mechanism.

Does sauna use protect the brain?

The same Finnish cohort produced a second widely shared finding. In a paper in Age and Ageing, the researchers looked at dementia in the same 2,315 men over the same median 20.7 years, during which 204 men were diagnosed with dementia and 123 with Alzheimer's disease.

Compared with once-a-week users, men who used a sauna 4 to 7 times a week had a hazard ratio of 0.34 for dementia and 0.35 for Alzheimer's disease. That is a large association.

The detail that rarely makes the headline is the middle group. For men using the sauna 2 to 3 times a week, the hazard ratio for dementia was 0.78, with a 95% confidence interval of 0.57 to 1.06. Because that range includes 1.0, the data cannot rule out no effect at all. Only the small group of very frequent users showed a clear difference, and that group was just 201 men.

For a founder in their 40s thinking about cognitive longevity, this is interesting and unproven. It is one cohort, of men only, in one region of Finland.

What about women, and does it hold up outside the original cohort?

The first studies were in men, which left an obvious gap. In 2018 the Finnish group published a follow-up in BMC Medicine on 1,688 people, 51.4% of them women, with an average age of 63 at the start and a mean follow-up of 15 years.

The University of Eastern Finland's summary reports that people who used the sauna once a week had 10.1 fatal cardiovascular events per 1,000 person-years, while those who went four to seven times a week had 2.7. Time spent mattered too: under 15 minutes a week was associated with 9.6 events per 1,000 person-years, and more than 45 minutes a week with 5.1.

The same summary is candid about the limits. It states that "the observational nature of the study does not allow for conclusions about cause and effect," and cautions that everyone in the study came from one region. That is the right way to read the entire body of Finnish sauna research.

Can a sauna help with stress or mood?

This is where founders often want the evidence to go further than it does. There is no large trial showing that regular sauna use treats anxiety, burnout or depression.

The closest rigorous evidence is a small trial of a medical heat treatment. In 2016, researchers published a randomized, double-blind trial in JAMA Psychiatry testing whole-body hyperthermia for major depressive disorder. Of 338 people screened, 34 were randomized and 29 provided at least one follow-up assessment. The control condition matched "all aspects of WBH except intense heat." Compared with the sham, the active group's depression scores were 6.53 points lower after one week and 4.27 points lower at week six. The authors called it a treatment that "holds promise."

Two cautions. First, this was a clinical hyperthermia device, not a Finnish sauna, and it was run by researchers. Second, 29 people is a pilot-sized sample. The trial is a reason for more research, not a reason to self-treat depression with heat. If you are dealing with persistent low mood, see a physician or licensed clinician.

What most regular sauna users will tell you, anecdotally, is simpler: 15 minutes in a hot, quiet room with no phone is one of the few times in the day when nothing is asking for their attention. That effect is real, even if nobody has measured it in founders.

What the evidence says, and what it doesn't

Reasonably strong: In long-running Finnish cohorts, frequent sauna use is consistently associated with lower cardiovascular and all-cause mortality, with a dose-response pattern (more sessions, lower risk). The acute effects on heart rate and blood flow are well described.

Suggestive: Lower dementia and Alzheimer's risk in very frequent users, based on one cohort of men, with a small high-frequency group and an unclear result for moderate use.

Early: A small randomized trial of medical whole-body hyperthermia for depression showed a benefit over sham. It does not tell us much about recreational sauna use.

Not established: That sauna use causes any of these outcomes. The Finnish data is observational. Men who could take a sauna most days may have differed in ways the adjustments could not fully capture, such as income, leisure time, social connection or baseline health. People who are already unwell may use the sauna less, which can make sauna use look protective. Findings from Finland, where sauna is woven into daily life, may not transfer neatly to a 45-year-old in Denver with a barrel sauna on the deck.

How founders can use heat sensibly this week

None of this is a prescription. It is a way to try heat without overreaching.

Check your baseline first. Harvard Health advises that "people with uncontrolled high blood pressure and heart disease should check with their doctors before taking a sauna." If you have not had your blood pressure checked recently, or you take medication that affects heart rate or sweating, talk to a physician before making sauna a habit.

Respect the safety basics. The same guidance says to avoid alcohol and medications that impair sweating before and after, stay in no more than 15 to 20 minutes, cool down gradually, drink water afterward, skip it when ill, and leave immediately if you feel unwell. Alcohol plus heat is the combination to take most seriously.

Anchor it to the end of the day, not the start. Many people find a warm session in the evening makes it easier to wind down, though the research does not prove this. If you try it, give yourself enough time to cool off before bed, and keep your wake time fixed. Our guide to meditation for sleep for executives covers the rest of that wind-down.

Leave the phone outside. Heat and screens do not mix well, and the value of the session partly comes from having nothing to respond to. Use the time to let your breath slow and notice what your body does as it heats up.

Keep the bigger levers in front. The Finnish men who used saunas often also lived a certain way. Sleep regularity, regular movement and real social contact have stronger and broader evidence behind them. We cover how those levers work in what chronic stress does to a founder's body.

Heat is a practice, not a hack

The most useful thing a sauna does for most founders may be the least measurable: it forces 15 minutes of stillness in a body that is under strong, safe physical stress. Learning to stay calm and present while your heart rate climbs is a skill with obvious carryover to a tense board meeting or a hard conversation with a co-founder.

That is the skill we train at Cinder. Private 1:1 coaching focuses on stress regulation and attention, so the downshift you find in a hot room is one you can reach on a Tuesday afternoon without one. If anxiety is what you are trying to settle, our piece on meditation for anxiety when you're a founder is a good next read.

Apply for private coaching

Sources

• Association between sauna bathing and fatal cardiovascular and all-cause mortality events, JAMA Internal Medicine, 2015
• Sauna bathing is inversely associated with dementia and Alzheimer's disease in middle-aged Finnish men, Age and Ageing (via University of Bristol), 2016
• Frequent sauna use associated with lower cardiovascular death rate in men and women, University of Eastern Finland, 2018
• Saunas and your health, Harvard Health Publishing, 2020
• Whole-body hyperthermia for the treatment of major depressive disorder: a randomized clinical trial, JAMA Psychiatry (via University of Arizona), 2016