Sauna and the heart: 20 years of observation

In Finland the sauna is not a trendy biohack but a part of daily life for generations. That made Finns an ideal population to study: researchers had people they could observe over a long time and in natural conditions.

What the Kuopio study showed

The prospective Kuopio Ischemic Heart Disease Risk Factor Study enrolled 2,315 middle-aged men (aged 42-60) from Eastern Finland. They were followed for an average of about 21 years. Participants were divided by sauna frequency: once a week, 2-3 times, and 4-7 times.

The results (published in JAMA Internal Medicine, by Laukkanen and colleagues) turned out to be notable. Among those who used the sauna 4-7 times a week, compared with once a week, there was:

• about 40% lower all-cause mortality;
• roughly 63% lower risk of sudden cardiac death;
• around 50% lower risk of death from cardiovascular disease.

Why it might work

The heat exposure of a sauna triggers responses that are in many ways similar to moderate cardio: the heart rate rises, blood vessels dilate, the endothelium is trained, and blood pressure drops. This regular "heat stressing" is viewed as one of the mechanisms behind the cardiovascular benefits.

Important caveats

This is an observational study. It shows an association but does not prove that the sauna itself lowers mortality: it is possible that healthier and more affluent people go to the sauna more often. The sample was middle-aged Finnish men, so the conclusions should be applied to everyone with caution. And the sauna is a complement, not a replacement for training. People with severe cardiovascular conditions, those who are pregnant and those with a range of illnesses need to consult a doctor.

Heat as "gentle exercise"

Why is heat able to imitate a workout at all? In a hot environment the body has to cool itself: the heart starts beating faster, peripheral blood vessels dilate to draw heat toward the skin, and sweating increases. In a sauna the pulse can climb to levels comparable to light or moderate physical exertion. Regularly repeating this gentle stress, the researchers hypothesize, trains the vascular system and improves the function of the endothelium — the inner lining of the blood vessels, whose condition does much to determine heart health. It is the same logic as in training: a measured stress followed by adaptation.

Where the line of common sense runs

"More is better" does not imply "the hotter and longer, the healthier." Overheating, dehydration and sharp swings (for example, jumping into ice water if you have heart problems) carry real risks. Alcohol in the sauna is a dangerous combination: it intensifies dehydration and the strain on the heart. The sensible practice is moderate temperature, a limited session length, enough water before and after, and attention to how you feel: dizziness, nausea or palpitations are a signal to leave immediately. The sauna is good as a regular gentle habit, not as an endurance contest.