Health & the Science of Heat

The Finnish studies that changed the conversation

The strongest evidence comes from the Kuopio Ischaemic Heart Disease study in Finland, where Dr. Jari Laukkanen's team followed more than 2,300 middle-aged men for over 20 years. Men who took a sauna 4–7 times a week had a dramatically lower risk of fatal cardiovascular events and all-cause mortality than once-a-week bathers. A follow-up analysis in Age and Ageing found the frequent bathers had a 66% lower risk of dementia and 65% lower risk of Alzheimer's disease. Further papers from the same cohort link regular sauna to lower rates of hypertension and stroke.

Why heat works

A proper sauna session raises your heart rate to 100–150 beats per minute — comparable to a brisk walk — while heat widens blood vessels and improves the function of the endothelium, the lining of your arteries. A 2018 review in Mayo Clinic Proceedings summarises the mechanisms: better vascular function, lower blood pressure, reduced inflammation. A 2023 randomized controlled trial even tested sauna in adults with coronary artery disease and found improved vascular health. Researchers increasingly describe sauna as "passive cardiovascular conditioning" — exercise-like benefits while you sit still and sweat.

The dose

In the Finnish data, benefits scale with frequency and duration: the sweet spot is 15–20 minutes per session, 4–7 sessions a week, at traditional temperatures (80–100 °C in a Finnish-style hot room). Less is still good — even 2–3 sessions a week showed measurable protection.

Honest cautions

Sauna is remarkably safe for healthy people — Finns take babies and grandparents alike — but: hydrate before and after; never mix sauna with alcohol; and if you have unstable heart disease, very low blood pressure, or are pregnant, talk to your doctor first. And two myths to retire: you do not "sweat out toxins" in any meaningful medical sense (your liver and kidneys do that), and the weight you lose in a session is water, not fat.

On my TV appearance I said there are a lot of misconceptions about sauna — this page is where I answer them with research.