Traditional Sauna vs Everything Else: Why the Finnish Study Matters

In 2015, a Finnish team published a paper that has become the citation behind a thousand sauna claims. The result was simple and provocative: among middle-aged Finnish men, higher frequency of sauna bathing correlated with significantly lower rates of sudden cardiac death, fatal coronary heart disease, fatal cardiovascular disease, and all-cause mortality. (PubMed)

That finding stuck because it wasn’t subtle, and it wasn’t based on “wellness scores.” It was based on hard outcomes tracked over a long period of time.

It also triggered the right kind of pushback: not “sauna is fake,” but “slow down-this is observational.”

A Summary of the Study

This was a prospective cohort study from Eastern Finland: 2,315 men aged 42–60 at baseline, followed for a median of 20.7 years. Over follow-up there were 190 sudden cardiac deaths and 929 all-cause deaths, among other fatal cardiovascular events. (American College of Cardiology)

Sauna exposure was measured by questionnaire at baseline. Participants were grouped by sauna frequency: once per week, 2–3 times per week, and 4–7 times per week. (American College of Cardiology)

Key Findings: The Important Numbers

The event rates moved in a tight gradient. For all-cause mortality, the proportion of men who died over follow-up was 49.1% in the once-per-week group, 37.8% in the 2–3× group, and 30.8% in the 4–7× group. (American College of Cardiology)

After adjusting for common cardiovascular risk factors, the association remained. For sudden cardiac death, compared with once per week, the adjusted hazard ratio was 0.78 for 2–3×/week and 0.37 for 4–7×/week (trend p = 0.005). the authors reported similar inverse associations for fatal coronary heart disease (CHD), fatal cardiovascular disease (CVD), and all-cause mortality. (American College of Cardiology)

One detail that keeps this from being a caricature: the paper also looked at session duration, and duration behaved differently than frequency. Longer sessions were linked with lower risk for sudden cardiac death and fatal cardiovascular outcomes, but not for all-cause mortality in the same way. (American College of Cardiology)

Why the criticism was inevitable and reasonable

JAMA Internal Medicine published a formal Comment & Response arguing the mortality link may be noncausal. (PubMed)

This wasn’t a contrarian stunt. It’s the standard, correct reaction to observational lifestyle data - especially when the effect looks large.

The critique boils down to two points:

First, confounding can be stubborn. People who sauna 4–7 times per week may differ in ways you can’t fully measure: routines, baseline health, social patterns, stress exposure, and other behaviors that cluster with a culturally normal habit. Statistical adjustment helps, but it doesn’t close the case.

Second, observational effects can look “too clean.” When a lifestyle exposure appears strongly protective, careful readers ask whether the exposure is acting as a marker for a broader life pattern.

The authors replied in the journal, defending the analysis while still staying in observational language (association, not proof). (PubMed)

What has changed since 2015

The important question isn’t “did we get a randomized mortality trial?” (we didn’t). The question is whether the total evidence base has grown in a way that makes the original finding harder to dismiss as a pure artifact.

Three developments matter.

A coherent physiological story is no longer optional hand waving

A major review in Mayo Clinic Proceedings synthesized the sauna literature and laid out plausible pathways by which repeated heat exposure could affect cardiovascular risk - blood pressure effects, vascular/endothelial function, arterial stiffness, autonomic modulation, and related changes. (PubMed)

Mechanisms don’t prove outcomes. They do, however, make it easier to take the observational associations seriously because they show the direction of effect isn’t physiologically mysterious.

Controlled studies have started to move relevant intermediates

Interventions don’t need to prove mortality to be informative. If repeated sauna exposure reliably improves intermediate markers that sit on the pathway to cardiovascular risk, that supports the idea that sauna can do more than simply “tag” healthy people.

One randomized controlled trial (8 weeks) reported that adding sauna bathing to an exercise program produced additional improvements in cardiorespiratory fitness and systolic blood pressure compared with exercise alone. (PMC)

That still doesn’t prove the 2015 mortality association is causal end-to-end. It does support the idea that heat exposure can produce causal physiological changes in the right direction.

The cautious conclusion is stronger than “it’s just correlation”

The original cohort result remains observational; the skepticism remains legitimate. But it’s no longer accurate to treat the mortality paper as an isolated curiosity. Between (a) the strength and dose-response of the original association, (b) explicit scholarly debate in the journal, (c) a more mature mechanistic framework, and (d) controlled work showing changes in intermediate cardiovascular markers, the “this probably reflects something real” interpretation has gained weight over time. (American College of Cardiology)

Where a careful reader can land today

Two statements can both be true:

1. The 2015 paper does not, by itself, prove sauna reduces mortality. That would require a different kind of evidence. (PubMed)

2. The broader research picture since then makes it increasingly difficult to explain the entire relationship as pure confounding. The most reasonable position is that sauna is likely doing something causal for cardiovascular physiology, even if the precise portion of the mortality association that is causal remains uncertain. (PubMed)

References

Association between sauna bathing and fatal cardiovascular and all-cause mortality events (2015) – PubMed record. (PubMed)
ACC Journal Scan summary with event rates, follow-up, and key hazard ratios. (American College of Cardiology)
Commentary: “The Link Between Sauna Bathing and Mortality May Be Noncausal.” (PubMed)
Authors’ reply to the noncausal critique. (PubMed)
Review: “Cardiovascular and Other Health Benefits of Sauna Bathing” (2018) – PubMed record / Mayo Clinic Proceedings. (PubMed)
RCT: “Effects of regular sauna bathing in conjunction with exercise …” (2022) – PubMed/PMC. (PubMed)