Heat-Induced Stress: The Health Benefits of a Sauna

The myriad of benefits associated with exercise is well known; regular physical activity decreases the risk of chronic conditions ranging from cardiovascular disease, diabetes, obesity, and cancer and can prolong an individual’s life (Warburton, Nicol, and Bredin, 2006). While exercise remains one of the most highly promoted and revered methods of maintaining a healthy lifestyle, research into other activities such as sauna bathing has elucidated a multitude of its own promising effects. Definitive evidence showing the physiological changes elicited by a sauna are surprisingly similar to that of exercise (Iguchi et al., 2012). By understanding the mechanisms of these processes, further insights into the fields of medicine and health science may be attained.

The sauna traditionally originated in Europe and continues to prevail globally, being used in virtually all facets of life, from recreational use to athletic rehabilitation (Scoon et al., 2007). In essence, a sauna refers to an enclosed space that is capable of maintaining an elevated temperature by controlling air humidity (Nore, Kraniotis, and Brückner, 2015). A variety of saunas exist,differing in the temperatures and methods of heat generation. The most notable forms include dry and wet saunas, with the former relying on a high temperature around 100°C and extremely low humidity, and the latter involving a lower temperature and extreme humidity (Nore, Kraniotis, and Brückner, 2015). The ability of a sauna to store heat is predicated on the use of hygroscopic construction materials. In particular, wood is very effective at buffering moisture; when water is poured on a sauna stone-oven, thereby increasing the relative air humidity, the dry wooden materials quickly absorb the moisture, consequently heating the room (Nore, Kraniotis, and Brückner, 2015).

When exposed to high temperatures, the innate human response dictated by the sympathetic nervous system is to raise the body temperature and perspire. On a micro scale, cells release heat shock proteins (HSPs), which facilitate the transport of repair proteins and prevent protein aggregation and denaturing (Iguchi et al., 2012). A particular HSP known as HSP72, which has been connected to successful immune function, is notably upregulated by thermal stress (Iguchi et al., 2012). A randomized control trial by Iguchi et al. (2012), wherein participants were exposed to whole-body heat-stress by sitting in a 73°C heat chamber for 30 minutes, determined the effects of a sauna on the human cardiovascular system, hormonal fluctuations, and extracellular proteins, such as HSP72. It was found that arterial blood pressure decreased by approximately 8 mmHg, and that the release of HSP72 was increased by an average of 49%, indicating that whole-body heat stress reduces the workload of the heart in a manner different from exercise, which increases blood pressure (Figure 1) (Iguchi et al., 2012). A similar study carried out by Lee et al. (2017), which used the same heat-stress conditions, supported these results, where additional cardiovascular parameters such as pulse wave velocity, systolic and diastolic blood pressure, and left ventricular ejection time were decreased. As such, saunas have been explored as a method for stimulating weight loss and improving the endurance of seasoned athletes, which would have conventionally employed some form of exercise regimen (Podstawski et al., 2014; Scoon et al., 2007).  

Overall, while the physiological effects incurred by saunas are convincing, there is a need for continued research. Although it may not serve to replace the health benefits of daily exercise, incorporating a sauna can be an effective way to incite similar biochemical changes, ultimately helping to improve one’s health.

References

Iguchi, M., Littmann, A.E., Chang, S.-H., Wester, L.A., Knipper, J.S. and Shields, R.K., 2012. Heat Stress and Cardiovascular, Hormonal, and Heat Shock Proteins in Humans. Journal of Athletic Training, [online] 47(2), pp.184–190. Available at: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3418130/> [Accessed 4 Sep. 2018].

Lee, E., Laukkanen, T., Kunutsor, S.K., Khan, H., Willeit, P., Zaccardi, F. and Laukkanen, J.A., 2017. Sauna exposure leads to improved arterial compliance: Findings from a non-randomised experimental study. European Journal of Preventive Cardiology, [online] 25(2), pp.130–138. Available at: <http://journals.sagepub.com/doi/10.1177/2047487317737629> [Accessed 4 Sep. 2018].

Nore, K., Kraniotis, D. and Brückner, C., 2015. The Principles of Sauna Physics. Energy Procedia, [online] 78, pp.1907–1912. Available at: <https://www.sciencedirect.com/science/article/pii/S1876610215020937> [Accessed 4 Sep. 2018].

Podstawski, R., Boraczyński, T., Boraczyński, M., Choszcz, D., Mańkowski, S. and Markowski, P., 2014. Sauna-induced body mass loss in physically inactive young women and men. The Scientific World Journal. [online] Available at: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4295591/> [Accessed 4 Sep. 2018].

Scoon, G.S.M., Hopkins, W.G., Mayhew, S. and Cotter, J.D., 2007. Effect of post-exercise sauna bathing on the endurance performance of competitive male runners. Journal of Science and Medicine in Sport, [online] 10(4), pp.259–262. Available at: <https://www.sciencedirect.com/science/article/pii/S1440244006001393> [Accessed 4 Sep. 2018].

Warburton, D.E.R., Nicol, C.W. and Bredin, S.S.D., 2006. Health benefits of physical activity: the evidence. Canadian Medical Association Journal, [online] 174(6), pp.801–809. Available at: <http://www.cmaj.ca/content/174/6/801.short> [Accessed 4 Sep. 2018].