Is Sitting in a Sauna Exercise Without Exercising?

Passive heat exposure is an ancient tradition found across many cultures, from the sweat lodges of Native Americans to the Finnish sauna. This practice continues evolving, and now includes steam rooms, hot tubs, and infrared boxes. Passive heat mimics aspects of a cardio workout, such as increased heart rate, core temperature, and vascular dynamics. But while researchers believe that sauna provides a stimulus that is akin to exercise, they aren't convinced that it can be a replacement. And despite these clear physiologic effects, the data for long-term health benefits is surprisingly thin, perhaps in part because heat treatments have until now been viewed more as convivial ways to relax than as real health interventions.

Sauna seems to be having a moment. And it's a moment with momentum. Mentions of sauna in the lay press are seasonal, but the trend is steadily up over the last decade, and increasingly so.

Sauna mentions in the lay press 2020 - 2026

The practice is simple: a short time spent in a very hot enclosure that rapidly increases core temperature, which upon exit rapidly returns to normal, sometimes accelerated by a cold shower or icy plunge. The mechanism is still dominated by hot tubs, traditional Finnish saunas, and steam rooms, but infrared and portable at-home saunas are catching on. Sweat lodges remain a much smaller but culturally important niche.

All this is a reflection of just how exquisitely sensitive we humans are to temperature. Our bodies' biochemical systems only can function normally within a very narrow temperature range, between 36- and 38-degrees C. Mildly increased temperature (a "fever") increases immune function and so can be helpful when one is ill with a viral or bacterial infection. But a core temperature above 40 degrees is damaging, and this condition ("heat stroke") is a medical emergency that requires rapid cooling with an ice bath. If untreated, cellular damage, blood-brain barrier disruption, and organ damage follow. Above 43 C brain and circulatory systems fail and death is inevitable.

The body protects itself from overheating by increasing blood flow to the skin where it can dump calories by a combination of direct radiation and evaporating sweat from the skin. This shift in blood allocation is dramatic: normally the skin gets only 5% of the blood pumped by the heart, but as core temperature rises as much as 50% of cardiac output is shunted to the skin, a 10-fold increase. The body really cares about temperature regulation, because it is literally a matter of life or death.

The physiologic effects of directing amounts of blood to the skin are both immediate and obvious, and are broadly similar to a cardio workout. During a typical 10-to-20-minute session core temperature increases by 1-2 °C and the body responds by reducing resistance to blood flowing to the skin. This shunts blood to the skin, and in order to maintain blood pressure the body increases heart rate to 100-150 beats per minute, and also increases systolic blood pressure and cardiac output. All of these changes quickly return to baseline if the body is allowed to cool off.¹ These acute cardiovascular responses have led several research groups to describe sauna exposure as a form of passive "exercise mimetic" stress on the cardiovascular system, a sort of "exercise without exercising".²

Beyond sauna's exercise-like effects, it also briefly turns on many of the body's cellular "stress-response" systems. In small studies, a single sauna session increases protective heat-shock proteins, stress hormones, and immune signals, and repeated sessions over days to weeks have been shown to raise white blood cell counts, tweak inflammatory markers, and improve measures of autonomic balance such as heart-rate variability. And while these changes are large enough that researchers consider them physiologically meaningful, it's unclear how they affect human health overall. We still don't know exactly how much they contribute to the long-term reductions in cardiovascular events that have been reported in observational Finnish cohorts.

Despite the obvious physiologic impact and the tantalizing immune changes, actual research documenting improved health or longevity is surprisingly rare. However, a few studies are available. For example, a widely cited paper appeared in the prestigious journal JAMA³ a decade ago that followed 2,315 Finnish middle-aged men for 21 years and found that sauna use lowered the risk of dying from sudden cardiac death, coronary heart disease, cardiovascular disease, as well as all-cause mortality. And the effect size was substantial: compared with men who went to the sauna once a week, men who went 4-7 times per week reduced their risk for all these outcomes by about 50% even after adjusting for standard cardiovascular risk factors. Longer sessions (> 19 minutes vs. < 11 minutes) were also associated with lower cardiovascular death risk. A second, larger study in a more diverse population of Fins also found that regular sauna use is associated with a lower risk of death from cardiovascular disease⁴. Still more recently a 2024 study published in the International Journal of Circumpolar Health confirmed these findings in a Swedish population⁵. Finally, a review article from 2018 in Mayo Clinical Proceedings⁶ summarized the available epidemiological, experimental, and interventional evidence and concluded that sauna bathing associated with a broad range of potential health benefits, including lower risks of hypertension, cardiovascular disease, stroke, dementia, and some respiratory and rheumatic conditions, as well as reduced all-cause mortality. Unfortunately, because all of these studies were observational, we can't be sure that sauna itself was responsible for the effects reported.

How big a deal is all this? It's hard to know exactly how to interpret "risk of dying". A much more natural measure would be "years of additional life provided by regular sauna practice". Unfortunately, this hasn't been studied, but if we allow a few reasonable assumptions, we can get from "risk of dying" to "years added to one's life" mathematically. Based on this approach it seems lifelong daily sauna may add as much as a few years to one's life span. Of course, it's too late for most of us to get in on a "lifelong" sauna practice, and "daily" is unrealistic for most people. But for those fortunate enough to have been born into the sauna culture of Finland, well, they may have hit the jackpot. Interestingly, "a few years" of added life is similar to the benefits computed for a lifelong daily practice of Tai Chi. And of course there are other, perhaps less exotic practices that can extend life: swimming, jogging, even just walking, all can make contributions to both lifespan and health-span.

But before those who missed the opportunity of lifelong sauna (or Tai Chi, or whatever), there is this consolation: a 1-hour sauna session every day from age 20 until death adds up to about two years sitting in a sauna, about equal to the time the practice might have extended one's life.

So, while sauna may extend one's life, it's only a bargain if one actually enjoys the practice. But if you do enjoy the ritual, then time in a sauna is a win-win.

 

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¹ Kukkonen-Harjula, K., Oja, P., Laustiola, K., Vuori, I., Jolkkonen, J., Siitonen, S., & Vapaatalo, H. (1989). Haemodynamic and hormonal responses to heat exposure in a Finnish sauna bath. European Journal of Applied Physiology and Occupational Physiology, 58(5), 543–550. https://doi.org/10.1007/BF02330710

² Cullen, T., Clarke, N. D., Hill, M., Menzies, C., Pugh, C. J. A., Steward, C. J., & Thake, C. D. (2020). The health benefits of passive heating and aerobic exercise: to what extent do the mechanisms overlap? Journal of Applied Physiology, 129(6), 1304–1309. https://doi.org/10.1152/japplphysiol.00608.2020

³ Laukkanen, T., Khan, H., Zaccardi, F., & Laukkanen, J. A. (2015). Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Internal Medicine, 175(4), 542–548. https://doi.org/10.1001/jamainternmed.2014.8187

⁴ Laukkanen, T., Kunutsor, S. K., Khan, H., Willeit, P., Zaccardi, F., & Laukkanen, J. A. (2018). Sauna bathing is associated with reduced cardiovascular mortality and improves risk prediction in men and women: a prospective cohort study. BMC Medicine, 16(1), Article 219. https://doi.org/10.1186/s12916-018-1198-0

⁵ Engström, Å., Hägglund, H., Lee, E., Wennberg, M., Söderberg, S., & Andersson, M. (2024). Sauna bathing in northern Sweden: results from the MONICA study 2022. International Journal of Circumpolar Health, 83(1), Article 2419698. https://doi.org/10.1080/22423982.2024.2419698

⁶ Laukkanen, J. A., Laukkanen, T., & Kunutsor, S. K. (2018). Cardiovascular and other health benefits of sauna bathing: a review of the evidence. Mayo Clinic Proceedings, 93(8), 1111–1121. https://doi.org/10.1016/j.mayocp.2018.04.008