Are saunas good for your heart? What the research shows

Sauna bathing has been a tradition in Finland for thousands of years, mainly for pleasure and relaxation, and it is becoming increasingly popular in many other populations. Over the past decade, research from Finland has linked regular sauna use with longer life, fewer deaths from heart disease, fewer strokes and a lower risk of dementia.

Those findings come mostly from one long-running Finnish study, analyzed by one research group. Evidence from elsewhere is thinner but points in a similar direction: a large Japanese study of hot baths found a comparable pattern, and small trials show short-term gains in blood pressure and heart failure symptoms. The clearest risk in the research is not the heat itself but drinking alcohol in the sauna.

What a sauna does to the body

Sitting in a hot sauna raises body temperature and heart rate, and the body responds by sweating heavily to cool itself.

Researchers have proposed several ways that repeated heat might help the heart over time. A 2018 review in Mayo Clinic Proceedings notes that it has been postulated that regular sauna bathing may improve cardiovascular function, through better widening of blood vessels, less stiff arteries, changes in the nervous system’s control of the heart, better blood fats and lower blood pressure. These are plausible mechanisms. Most have been measured over hours or weeks rather than tied directly to fewer heart attacks.

What the Finnish sauna studies found

The best-known evidence, published in JAMA Internal Medicine in 2015, comes from the Kuopio Ischemic Heart Disease Risk Factor Study. It enrolled 2,315 men aged 42 to 60 in eastern Finland between 1984 and 1989, recorded how often and how long they used a sauna, and followed them for a median of about 21 years.

Deaths from any cause occurred in 49.1% of once-a-week users, 37.8% of men who used a sauna two to three times a week and 30.8% of the 201 men who went four to seven times. After accounting for other heart risk factors, the most frequent users had about 63% lower risk of sudden cardiac death than once-a-week users. The authors concluded that increased frequency of sauna bathing is associated with a reduced risk of sudden cardiac death, fatal heart disease and death from any cause.

The same cohort later added women. In a Neurology study of 1,628 men and women aged 53 to 74, people who used a sauna four to seven times a week had about 61% lower risk of stroke than once-a-week users over 15 years. The authors reported the finding for men and women who take frequent sauna baths, with no difference in the pattern by sex. An analysis of the original men also linked frequent sauna use with about a third of the dementia risk of once-a-week users, and its authors wrote that moderate to high frequency of sauna bathing was associated with lowered risks of dementia.

Evidence from outside the Finnish sauna cohort

All of those numbers come from one cohort in one region, studied by overlapping teams of researchers. Independent confirmation matters, and the closest comes from Japan, from a study of hot tub bathing rather than saunas.

A study published in Heart in 2020 followed 30,076 Japanese adults aged 40 to 59 for about 20 years. People who bathed in a hot tub almost every day had about 28% lower risk of cardiovascular disease and 26% lower risk of stroke than people who bathed two times a week or less, after adjusting for the usual heart risk factors and diet. The authors concluded that the frequency of tub bathing was inversely associated with cardiovascular risk, meaning more frequent bathing went with lower risk.

One result differed from Finland. In the Japanese study, no associations were observed between tub bathing frequency and risk of sudden cardiac death, the outcome with the strongest link in the Finnish men. Hot baths and saunas are also not the same exposure, so the Japanese findings support the broader idea that regular heat may be good for the heart without confirming the Finnish numbers.

What sauna trials show

Trials can separate the heat from the kind of person who likes saunas, but sauna trials have been small and short. A 2018 systematic review by researchers outside the Finnish group found 40 clinical studies of regular dry sauna use involving 3,855 participants. Only 13 studies were randomized controlled trials and most studies were small, often with fewer than 40 people, and they measured very different outcomes.

Two trials give a sense of what regular heat can do. In a Finnish trial of 47 inactive adults with at least one heart risk factor, published in 2022, people were assigned to exercise, exercise followed by a 15-minute sauna, or neither, for eight weeks. Adding the sauna lowered systolic blood pressure, the top number, by 8 mmHg more than exercise alone, and improved fitness and total cholesterol. The authors, who include members of the Kuopio research group, wrote that sauna bathing demonstrated a substantially supplementary effect on top of exercise.

In Japan, the WAON-CHF trial randomly assigned 149 people in hospital with advanced heart failure to usual care or to 10 days of Waon therapy, a warm infrared sauna at 60 C for 15 minutes followed by 30 minutes of rest under a blanket. Symptoms, walking distance and heart size on x-ray improved in the Waon group, and no serious adverse events were observed in either group. A blood marker of heart strain did not change by more than chance could explain.

What the research shows about sauna risks

Harms have been studied far less than benefits. The 2018 systematic review found only one small study reporting an adverse effect, a drop in sperm production in men that reversed when they stopped using saunas, and concluded that more data of higher quality is needed on the frequency and extent of adverse side effects.

The clearest danger in the research is alcohol. A Korean study in Forensic Science, Medicine and Pathology set out to determine the role of alcohol intoxication in sauna deaths nationwide from 2008 to 2015. Of 103 people who died in saunas, 76 had a blood alcohol concentration of 0.08% or more at autopsy. Most of the intoxicated people who died were men, and more of them were found face down. The authors saw the pattern as a target for preventing alcohol-related sauna deaths.

Heat stroke, the most serious heat illness, is life-threatening and needs emergency care.

Why the sauna evidence is hard to interpret

The long-term findings are observational. Frequent sauna users may be healthier, more relaxed or better off to begin with, and people who are already unwell may avoid saunas, which can make heat look protective. In the Finnish study, sauna habits were measured once, decades ago, and only 201 men were in the most frequent group.

The trials are small, short and tested specific settings, from post-exercise sessions to hospital treatment for heart failure. None followed people long enough to count heart attacks, strokes or deaths. The Japanese study is independent but measured hot baths, not saunas.

What the sauna evidence adds up to

Regular sauna use is consistently linked with fewer heart deaths, strokes and dementia in one well-studied Finnish cohort, and near-daily hot baths show a similar link with heart disease and stroke in a large Japanese study. Small trials suggest regular heat can lower blood pressure in the short term and ease heart failure symptoms under medical supervision.

What the research cannot yet show is that taking up saunas lowers anyone’s long-term risk of heart disease or dementia. Alcohol stands out as the main danger, and how a person’s body handles heat depends on their health and medicines.