Heat as Medicine: What Forty Years of Sauna Research Asks of Us

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Every tradition I have studied has a heat ritual. The sweat lodge. The Russian banya. The Japanese onsen. The temazcal. Heat has always been where people went to be cleansed, to grieve, to pray and to reset.

What is new is that science has started to measure what those traditions knew. And for women in our second chapter, the findings are some of the most compelling in all of longevity research.

The Finnish cohort that changed the conversation

In eastern Finland, a long-running study called the Kuopio Ischaemic Heart Disease Risk Factor Study (KIHD) asked 2,315 men aged 42 to 60 how often they used a sauna, then followed them for a median of about 21 years.

Compared with men who used the sauna once a week, men who used it four to seven times a week had a markedly lower risk of sudden cardiac death (hazard ratio 0.37), and similar associations were seen for fatal heart disease, fatal cardiovascular disease and death from all causes. Sessions longer than 19 minutes were associated with a lower risk of sudden cardiac death than sessions under 11 minutes (Laukkanen et al., 2015).

The same cohort later linked frequent sauna use with a lower risk of dementia. The most frequent bathers had about a third of the risk of those who went once a week (hazard ratio 0.34) (Laukkanen et al., 2017).

And for women?

The original KIHD cohort was male, which is a real limitation. So the researchers followed a second group of 1,688 Finnish adults aged 53 to 74, more than half of them women. Over 15 years, higher sauna frequency and longer duration were each associated with lower cardiovascular mortality in both men and women, with no threshold effect: more was associated with lower risk, in a straight line (Laukkanen et al., 2018).

Here is the honest frame. These are observational studies. Finns who sauna often may differ from those who do not in ways that are hard to fully adjust for. They show a strong association, not proof. But the pattern is consistent, dose-dependent and supported by experimental work, which is why I take it seriously.

What heat does inside the body

Heat shock proteins

When your core temperature rises, your cells respond by producing heat shock proteins. These are molecular chaperones that help other proteins keep their proper shape under stress. Researchers consider them one of the key mechanisms through which repeated heat may support cardiovascular and cellular health (Brunt & Minson, 2021). This is hormesis: a small, controlled stress that teaches the body to become more resilient (Patrick & Johnson, 2021).

The vascular effect

Heat therapy behaves, in some ways, like gentle exercise for your blood vessels. In an eight-week controlled trial, young sedentary adults who did repeated hot-water immersion improved flow-mediated dilation (a measure of how well arteries relax), reduced arterial stiffness and lowered blood pressure compared with a sham group (Brunt et al., 2016).

The nervous-system downshift

This is the part I feel most, and the part I believe matters most for women carrying a great deal.

In a study of 93 adults with an average age of 52, a single 30-minute sauna session at 73°C raised heart rate, as you would expect. But during the cooling-down period afterwards, heart rate variability shifted toward parasympathetic dominance, the rest-and-restore state, and resting heart rate at the end of recovery was lower than before the sauna (Laukkanen et al., 2019).

The heat is the stress. The cool-down is the medicine.

Do not rush out of the sauna and into your inbox.

Researchers are also studying heat and mood. In a small randomized trial, a single session of medically supervised whole-body hyperthermia (not a home sauna) improved mood scores compared with a sham session for six weeks (Janssen et al., 2016). It is early, and it is not a reason to replace care, but it is a fascinating window.

Infrared or traditional: how to choose

Sauna temperatures range from about 45°C to 100°C (113°F to 212°F) depending on the type (Patrick & Johnson, 2021).

Traditional Finnish sauna. Heated air, often with water on hot stones for bursts of steam. Hotter, more intense, and this is the type studied in the Finnish cohorts. If you want to match the research most closely, this is it.

Infrared sauna. Infrared emitters warm the body more directly at a lower air temperature. Many women find it gentler and easier to stay in. The evidence is smaller but encouraging: in a two-week trial, daily far-infrared sauna at 60°C improved impaired blood-vessel function in 25 men with cardiovascular risk factors (Imamura et al., 2001).

My honest view: the best sauna is the one you will actually use. If extreme heat makes you miserable, or triggers hot flashes you would rather not invite, infrared may be the ritual you keep. If you love intensity and steam, go traditional.

Ready to choose one? I have written the full buying guide, from heaters and electrical needs to real costs and safety: Choosing a Home Sauna: What the Research Actually Supports.

The protocol

Based on the research and my own practice:

• Frequency: aim for four or more sessions a week. That is where the strongest associations appear (Laukkanen et al., 2015; Laukkanen et al., 2018).
• Duration: build gradually toward about 20 minutes in a traditional sauna (Laukkanen et al., 2015). Infrared sessions often run a little longer at the lower temperature.
• Cool down: sit quietly for 10 to 20 minutes afterwards. This is where the downshift happens.
• Hydrate, and never combine sauna with alcohol.
• Listen: leave if you feel dizzy, nauseous or unwell.

Thinking about a home sauna as an investment

A home sauna is a significant purchase, and I want to frame it the way I frame every investment piece: by cost per use.

If you use a sauna four times a week for ten years, that is about 2,080 sessions. An $8,000 cabin works out to just under $4 a session before electricity and installation. That is less than many of us spend on a single coffee, for a ritual associated with heart health, brain health and a calmer nervous system.

These are the four I would consider.

A closing thought

What the heat traditions teach is that heat is not something you endure. It is something you surrender to. The body softens, the breath lengthens, and for a few minutes the mind stops negotiating.

The research gives us permission to take that seriously. Make it a ritual, not a chore. Let it become the place you come home to.

The body holds the work. These are the tools that hold the body.

— Gillian

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