Is a sauna good for your heart? What the studies show

What did the Finnish study find?

The best-known result comes from the Kuopio Ischaemic Heart Disease study. Between 1984 and 1989, researchers asked 2,315 men aged 42 to 60 in eastern Finland how often and for how long they used a sauna, then followed them for a median of almost 21 years.

Compared with men who had one sauna a week, after adjusting for age, smoking, blood pressure, cholesterol and other risk factors:

• Sudden cardiac death was 22% less likely in men who had two or three sessions a week and 63% less likely in men who had four to seven. The first figure could have been chance; the second was not.
• Fatal heart disease, all heart and circulation deaths, and death from any cause followed the same pattern.
• Longer sessions mattered too. Men who stayed in for more than 19 minutes had about half the risk of sudden cardiac death of men who stayed in for under 11 minutes.

Only 201 of the men used a sauna four to seven times a week, so the estimates for that group are less precise than the headline numbers suggest.

Does it apply to women?

Probably. A later analysis of 1,688 men and women from the same region, half of them women and with an average age of 63, found the same pattern. After full adjustment, people who used a sauna four to seven times a week were 77% less likely to die of heart or circulatory disease over 15 years than once-a-week users. Risk fell steadily with each extra session.

A study of 1,628 men and women from the same group found that four to seven sessions a week were linked with 62% fewer strokes, and the link was the same in men and women.

Is it the sauna, or the people who use it?

That is the big question. People who can take a sauna most days may have more free time, more money, a sauna at home, better health to begin with or other healthy habits. The researchers adjusted for many of these, including income, physical activity and fitness measured on an exercise bike, and the links held. But no observational study can rule out every hidden difference.

Two things make a real effect more plausible:

• There is a dose-response pattern. More sessions and longer sessions went with lower risk, in step.
• Short trials show changes in the right direction. In a study of 102 adults with at least one heart risk factor, a single 30-minute session at 73°C lowered systolic blood pressure from 137 to 130 mmHg on average and made the main artery less stiff. In an American trial, eight weeks of regular hot-water immersion, which heats the body in a similar way, improved blood vessel function and lowered blood pressure compared with a lukewarm bath.

What is missing is a long randomised trial that assigns people to frequent saunas and counts heart attacks and deaths. That may never be done, which is why we grade this evidence as moderate rather than strong.

How does a sauna affect the heart in the short term?

During a session, your heart rate climbs, often to levels you would see in brisk walking or light jogging, and blood vessels in the skin widen to shed heat. The heart pumps more blood each minute, but the work is spread across a wider network of open vessels. After you come out, blood pressure dips below where it started. What heat does to the body explains each stage.

Does it matter how fit you are?

Yes. In 2,277 Finnish men followed for 26 years, high fitness was linked with roughly half the risk of dying from heart disease. Frequent sauna use was linked with a smaller fall in risk. Men who were both fit and frequent sauna users had the lowest risk of all, 58% below men who were unfit and used a sauna rarely. A sauna is a complement to exercise, not a replacement.

What about people with heart failure?

In Japan, a gentle form of infrared heat therapy called Waon therapy (a 60°C infrared sauna for 15 minutes, followed by 30 minutes resting under a blanket) has been studied in people with chronic heart failure. In one study of 129 patients with severe heart failure, cardiac events over five years were much less common in the group given Waon therapy than in a matched group who were not. It was not randomised, and this is a medical treatment, not a public sauna. If you have heart failure, talk to your heart team before using any sauna.