A Finnish study proves that a sauna session mobilizes your defenses against viruses in just 30 minutes
In the dry heat of a Finnish sauna, the body doesn’t just sweat. A new study carried out in Finland shows that in thirty minutes, heat causes more white blood cells to flow into the blood, the very ones which defend the body against viruses and bacteria.
Researchers from the University of Eastern Finland and the University of Turku followed 51 adults during a dry steam bath at 73°C, typical of a Finnish sauna. By analyzing blood samples before, just after and then half an hour after the session, they detailed how the duo sauna immune system actually works.
Sauna and immune system: what the Finnish study shows
Each participant stayed in the cabin for 30 minutes, with a short cold shower in the middle and the opportunity to drink. The average body temperature rose from 36.4°C to 38.4°C, a mild artificial fever. Immediately afterwards, the total number of
white blood cells in the blood increased in all.
Neutrophils and lymphocytes, two large families of immune cells, increased sharply and then returned to their initial levels within half an hour. Another group, MXD cells (monocytes, eosinophils and basophils), remained higher thirty minutes after the session, a sign of slightly more lasting mobilization.
In the blood, a lightning mobilization of white blood cells
For Ilkka Heinonen, researcher at the Academy Research Fellow at the University of Turku, the explanation lies in the movement of these cells: “This could indicate that the sauna mobilizes additional white blood cells from the tissues, which then redeposit them into the bloodstream after the session. This periodic release of white blood cells into the bloodstream is beneficial because once freed from their storage sites, they are better able to patrol the body and fight pathogens“.
The authors compare this reaction to that observed during physical effort: a brief increase in leukocytes which improves immune surveillance throughout the body, before a rapid return to normal.
Temperature, cytokines and what we can conclude from them
The researchers also measured 37 cytokines, these messengers of inflammation. On average, the levels changed little, but their evolution depended on the rise in temperature: “Interestingly, the levels of several cytokines changed depending on the magnitude of the rise in body temperature during sauna bathing. No similar association was observed between white blood cell count and changes in body temperature“, specifies Professor Jari Laukkanen, who led the study.
Regular sauna attendance is linked to various health benefits, and these recent findings may shed some light on how these benefits manifest in the body. However, the researchers point out that the study only focused on a sauna session and its immediate effects. Thus, it is not possible to draw definitive conclusions regarding long-term health impacts.