Association Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality Events

Executive summary

This is the study most often summarised as evidence that saunas extend life, and it is worth reading carefully because what it actually reports is narrower and more interesting than the headline.

Researchers followed 2,315 middle-aged Finnish men, aged 42 to 60 at recruitment, drawn from the Kuopio Ischemic Heart Disease Risk Factor Study. Sauna habits were recorded once, at baseline examinations conducted between 1984 and 1989, and the men were then followed for a median of 20.7 years while deaths were recorded.

Men who reported using a sauna 4 to 7 times a week had substantially fewer fatal cardiac events than men who used one once a week. After adjustment for conventional cardiovascular risk factors, the hazard ratio for sudden cardiac death in the most frequent group was 0.37 (95% CI 0.18-0.75), with a statistically significant trend across the three frequency groups. Longer individual sessions showed a similar pattern.

The design is observational. The men were not assigned to a sauna schedule; they reported the habits they already had. That means the study demonstrates an association, and the authors themselves call for further work to establish the mechanism. It also studied traditional Finnish saunas, which operate far hotter and with the option of humidity, not the infrared cabins sold for home use.

For a buyer, the practical value is not the hazard ratio. It is the dose pattern: whatever is going on here appears in the men who used a sauna most often and for longest, not in occasional users. That is an argument about habit and access, and it is the one honest thing this study says about buying equipment.

Why this research matters

This paper is the origin of most sauna marketing. Almost every claim about saunas and heart health, and a good deal of the general 'saunas help you live longer' framing, traces back to this cohort or to reviews built on it. Reading what it actually measured is the fastest way to judge whether a claim you have been shown is supportable.

It is also a clean example of a question that matters throughout this category: what an observational study can and cannot tell you. The finding is real, sizeable, and consistent across four separate outcomes. It is still not proof of cause.

What the researchers found

Over the follow-up period the cohort recorded 190 sudden cardiac deaths, 281 fatal coronary heart disease events, 407 fatal cardiovascular disease events and 929 deaths from any cause.

Unadjusted event rates fell as sauna frequency rose. Sudden cardiac death occurred in 10.1% of the once-weekly group, 7.8% of the 2-3 times weekly group and 5.0% of the 4-7 times weekly group. All-cause mortality followed the same pattern: 49.1%, 37.8% and 30.8% respectively.

After adjustment for cardiovascular risk factors, and using once-weekly bathing as the comparator, the hazard ratio for sudden cardiac death was 0.78 (95% CI 0.57-1.07) for 2-3 sessions per week and 0.37 (95% CI 0.18-0.75) for 4-7 sessions per week, with a P for trend of .005. Note that the middle group's confidence interval crosses 1.0, meaning that result on its own is not statistically significant. Comparable associations were reported for coronary heart disease, cardiovascular disease and all-cause mortality, each with a P for trend of .005 or lower.

Session duration showed a similar gradient. Compared with sessions under 11 minutes, the adjusted hazard ratio for sudden cardiac death was 0.93 (95% CI 0.67-1.28) for 11-19 minute sessions and 0.48 (95% CI 0.31-0.75) for sessions longer than 19 minutes, P for trend .002. Duration was significantly associated with fatal coronary and cardiovascular events but not with all-cause mortality.

What the results mean

A hazard ratio of 0.37 means that, over the follow-up period, the most frequent sauna users experienced sudden cardiac death at roughly a third of the rate seen in once-weekly users, after accounting for the risk factors the researchers measured. The confidence interval of 0.18 to 0.75 tells you the plausible range around that estimate; because it does not cross 1.0, the association is statistically significant.

What is reasonably supported is that frequent, longer traditional sauna bathing is associated with lower cardiovascular mortality in this population, that the association follows a dose pattern, and that it survives adjustment for the obvious confounders.

What remains uncertain is why. Three explanations fit the data equally well: sauna bathing produces a physiological benefit; men healthy enough to sauna four to seven times a week were already at lower risk for reasons not captured at baseline; or sauna frequency is a marker for something else entirely, such as affluence, leisure time or social connection. The study cannot separate these, and the authors do not claim to.

Strengths and limitations

Strengths

• Large sample for a cohort of this depth, with 2,315 participants.
• Exceptionally long follow-up, at a median of 20.7 years.
• Prospective design: sauna habits were recorded before any of the outcomes occurred.
• Hard, objectively ascertained endpoints - death and cause of death - rather than self-reported wellbeing.
• A clear dose-response gradient across both frequency and session duration, which is one of the classic criteria for taking an observational association seriously.
• Adjustment for an established set of cardiovascular risk factors.

Limitations

• Observational design; residual and unmeasured confounding cannot be excluded.
• Exposure was self-reported and measured only once, at baseline, then assumed to persist over two decades.
• Only 201 men were in the highest-frequency group, which is why that confidence interval is wide.
• Reverse causation is plausible: men already unwell may sauna less, rather than less sauna making men unwell.
• Men only, single country, single ethnic group.
• Sauna temperature, humidity and construction were not characterised, so the exposure cannot be reproduced precisely.
• The intermediate frequency group did not reach statistical significance on its own for sudden cardiac death.

Evidence in context

The finding has been reinforced within the same research programme rather than independently replicated. The same Kuopio cohort produced an associated analysis reporting lower dementia and Alzheimer's disease diagnoses at higher sauna frequency, and the group has since published broader reviews of the sauna literature. That consistency is real, but much of it comes from one cohort and one research group, which limits how far it can be treated as independent confirmation.

A separate systematic review of dry sauna bathing across 40 studies found that most reported beneficial effects, while noting that only 13 were randomised trials and most were small. Nobody has run a randomised trial with mortality as an endpoint, and given the follow-up such a trial would need, nobody is likely to.

The evidence base has therefore broadened since 2015 without becoming stronger in design. It remains observational at its core.

Related research

1. Sauna bathing is inversely associated with dementia and Alzheimer's disease in middle-aged Finnish men Laukkanen T, Kunutsor S, Kauhanen J, Laukkanen JA. Age and Ageing 46(2):245-249. 2017. PMID 27932366; doi:10.1093/ageing/afw212.The companion analysis from the same cohort, reporting lower dementia and Alzheimer's diagnoses at higher sauna frequency, and carrying the same observational limits.
2. Cardiovascular and other health benefits of sauna bathing: a review of the evidence Laukkanen JA, Laukkanen T, Kunutsor SK. Mayo Clinic Proceedings 93(8):1111-1121. 2018. PMID 30077204; doi:10.1016/j.mayocp.2018.04.008.A review by the same group placing this cohort alongside the wider experimental and epidemiological sauna literature.
3. Clinical effects of regular dry sauna bathing: a systematic review Hussain J, Cohen M. Evidence-Based Complementary and Alternative Medicine 2018:1857413. 2018. PMID 29849692; PMC5941775; doi:10.1155/2018/1857413.An independent systematic review of 40 dry sauna studies, useful for judging how strong the field is overall rather than how strong this one paper is.
4. Far-infrared saunas for treatment of cardiovascular risk factors: summary of published evidence Beever R. Canadian Family Physician 55(7):691-6. 2009. PMID 19602651; PMC2718593.The nearest thing to infrared-specific evidence, and a good illustration of how much smaller that literature is.
5. Does the combination of Finnish sauna bathing and other lifestyle factors confer additional health benefits? A review of the evidence Kunutsor SK, Laukkanen JA. Mayo Clinic Proceedings 98(6):915-926. 2023. PMID 37270272; doi:10.1016/j.mayocp.2023.01.008.A later review examining sauna bathing in combination with other lifestyle factors, relevant to the confounding question this study cannot resolve.