How Sauna Use Supports Cardiovascular Health

All right, we're going to switch gears and we're going to talk about another type of stress. Exercise is one type of stress. We're going to talk about thermal stress from deliberate heat exposure. If anyone in here has done a hot tub, sauna, steam shower, or hot yoga, they know that a lot of the physiological responses are very similar to moderate-intensity exercise. So as you're sitting in the hot tub, as you're sitting in the hot sauna, your heart rate starts to go up. You start to feel hot. You start to feel uncomfortable. You start to sweat. A lot of the same physiological processes that happen when you're doing moderate-intensity exercise, not vigorous-intensity exercise, happen when you expose yourself deliberately to heat: increased heart rate, increased stroke volume, and increased cardiac output. In fact, there's been a head-to-head comparison looking at sauna versus a stationary bike. So individuals did about 100 watts on a stationary bike for about 15 minutes or they were in a hot sauna for about 15 minutes. And the physiological responses that were measured were identical. So during the activity, heart rate went up, blood pressure went up. After the activity, whether it was sauna or stationary cycling, blood pressure improved compared with baseline. Resting heart rate was also lower. So, in the head-to-head comparison, sauna mimicked moderate-intensity physical activity.

Studies have also compared exercise alone with exercise plus sauna. Observational data show that people in Finland who exercise have a longer life expectancy than those who do not, but people who exercise and use a sauna have a longer life expectancy than people who only exercise. So in other words, there seems to be an additive effect on life expectancy. There have also been intervention trials in Finland. Dr. Jari Laukkanen, a friend of mine, is probably one of the world's leading experts on sauna research. He took a cohort of participants and split them into two groups. One group was using a stationary bike. The other group was using a stationary bike and then getting into a hot sauna. In this case, the sauna session was only about 15 minutes at 175 to 179 degrees Fahrenheit. He measured their cardiorespiratory fitness at baseline and after the intervention and a variety of other biomarkers as well. What he found was that exercise plus sauna improved cardiorespiratory fitness more than exercise alone, which isn't that hard to believe considering I just told you that sauna is like an exercise mimetic. So you're essentially extending the time of your workout.

There were also greater improvements in blood pressure and lipid biomarkers compared with exercise alone. Data from Dr. Jari Laukkanen's lab have shown that men who used the sauna two to three times a week have about a 22% lower risk of sudden cardiac death than men who used the sauna one time a week. Men who used the sauna four to seven times a week have about a 63% lower risk of sudden cardiac death than men who used it one time a week. Now, if you think about sudden cardiac death and heart attacks, you want to survive a heart attack if one occurs. In the US, someone has a heart attack about every 30 seconds. Surviving it is significant. They were 63% less likely to die from sudden cardiac death if they were using the sauna four to seven times a week.

And by the way, saunas in Finland are very ubiquitous. There's also a lot of public saunas, as they call them, that are free. So a lot of people have access to saunas. His data also showed that, in a dose-dependent manner, sauna use was associated with a lower risk of all-cause mortality. In this case, men who used the sauna two to three times per week had about a 24% lower risk of all-cause mortality. If they boosted that up to four to seven times a week, they had a 40% lower risk of all-cause mortality than men who used the sauna one time a week. They also had a lower risk of cardiovascular-related mortality, again in a dose-dependent manner. If they went up to four to seven times a week, that was a 50% lower risk of cardiovascular-related mortality than men who used it one time per week.

So, we're seeing this clear dose response here. These data were adjusted for many different types of confounding factors. Physical activity, lipids, type 2 diabetes, diet, and many other factors were considered. In addition, Dr. Laukkanen studied a cohort of people who had type 2 diabetes. Even in those cohorts, sauna use was associated with lower all-cause and cardiovascular-related mortality. So it really seems to be a true phenomenon that's being observed. We'll get to some of the intervention data that kind of corroborates it. Sauna use was also associated with lower stroke risk in a dose-dependent manner. Again, two to three sessions per week were associated with a 14% lower stroke risk.

This was in both men and women. Compared with one session per week, four to seven sessions per week were associated with a 61% lower stroke risk. These are pretty phenomenal numbers we're talking about here. And I know I spent the first 30 minutes of my talk talking about vigorous-intensity exercise, but we are all in the real world and there are many people who won't put in that effort. And it's a lot easier to get some people to sit in a spa, hot tub, or hot sauna than to get them to do a 10-minute Peloton interval, right? Maybe you can get the exercise snack in. I think that is definitely doable, and it is relevant to many people who are not going to engage in physical activity or who are injured and can't, right? So I think it opens a lot of doors.

Sauna use is also linked to a lower risk of hypertension in a dose-dependent manner. Data dating back decades show that hot baths and hot tubs lower blood pressure as well. With sauna use two to three times per week, you get about a 24% lower risk of hypertension. Increase that to four to seven times per week and you get a 46% lower risk. You want to see dose dependence in observational data because those data cannot establish causation. A dose-response pattern strengthens the observation.

Intervention trials have also shown improved blood pressure after a single sauna session and after multiple sessions. The sauna causes vasodilation. As I said, it increases cardiac output during the session. Many of the same physiological changes occur when you engage in moderate-intensity physical activity. Most of the parameters used in those studies came from Finland. In Finland, typical sauna temperatures are around 174 to 179°F. They also often put water on hot rocks to create about 20 to 30% humidity, and that does make it feel hotter as well.

The duration spent in the sauna is very important. For example, in the sudden cardiac death study, the effect was much smaller when the men stayed in the sauna for only 10 minutes. They had only an 8% lower risk of sudden cardiac death with two to three sessions per week, versus about a 25% lower risk with longer sessions. The sweet spot was staying in the sauna for more than 19 minutes. So I like to say 20 minutes is the sweet spot because once they hit that 20-minute mark, they were getting the most robust effect. So really duration is important. Frequency was also dose-dependent. At two sessions per week, you're going to get at least some benefits. The maximum dose is four to seven times per week.