Johannes Kettelhodt makes a deceptively simple argument: heat is medicine, but only if you train your body to receive it. That framing — "you have to train your body to get used to that heat" — keeps circling back through this conversation, and it's the right place to anchor everything else. Not the sauna itself. The adaptation. The consistent, deliberate exposure that gradually shifts your physiology.
The 20-30% mortality reduction for four to seven sessions per week is the headline number. But it undersells what the research actually shows.
The 2023 academic paper on sauna and neurocognitive disease in our knowledge base takes things further: frequent sauna users show a 65% reduced risk of Alzheimer's and a 66% lower risk of dementia. These aren't marginal effects. These are numbers that pharmaceutical researchers fund entire clinical trials trying to achieve — and here, the intervention is sitting in a hot room several times per week.
The MONICA study on Northern European sauna bathing adds another layer: regular sauna users report higher happiness, better energy, and improved sleep. This matters because we tend to isolate sauna benefits into cardiovascular or cognitive buckets. The lived experience is more holistic than that. People who sauna regularly feel better — and they sleep better — and those two things compound over years.
On the cardiovascular mechanism, there's broad consensus. Your heart rate climbs, plasma volume increases, vasculature dilates. You're mimicking moderate aerobic exercise without the joint load or cortisol spike. Heat shock proteins step in to refold or clear misfolded proteins — cellular housekeeping that becomes more valuable with every passing decade.
The infrared question is where reasonable people diverge. Kettelhodt is measured and honest: traditional saunas have a deeper scientific foundation. The longitudinal population data — the Finnish studies, the MONICA data — comes almost entirely from traditional sauna research. Infrared may have real applications for tissue healing and lower-temperature access, but we're working with far thinner evidence over far shorter timescales.
If you have access to a traditional sauna: three to four sessions per week, 15-20 minutes at 80-90 degrees Celsius. Acclimate before pushing duration. Cool down properly — room temperature first, then cold if you're incorporating contrast. Hydrate. If traditional isn't available, infrared at 60-70 degrees for 20-30 minutes is a reasonable alternative. Chase consistency over intensity. The mortality data lives in habit, not heroics.
Finland has roughly one sauna for every five people. Two million saunas for a population under ten million. This isn't a wellness trend — it's a centuries-long population-level experiment. And what that experiment tells us, through the MONICA data and decades of Finnish health outcomes, is that cultures which build heat exposure into the fabric of daily life tend to live longer and think more clearly. Not because of genetics. Because they ritualized the practice until it stopped being a choice.
That's the real lesson here. Not to install a sauna. To make heat exposure so routine it disappears into the rhythm of the week. That's where the data lives, and that's where the results follow.