Spending 30 minutes in a sauna followed by a brief cold shower triggers a rapid increase in white blood cells circulating in the bloodstream, according to a new study from Finland. The findings suggest that this heat exposure routine temporarily mobilizes immune cells from tissues, allowing them to patrol the body more effectively against potential pathogens.
The research, led by the University of Eastern Finland and the University of Turku, examined the immediate physiological effects of sauna bathing on the immune system. The study involved 51 adults with an average age of 50. Participants underwent a single sauna session that included a mid-session cold shower. Researchers measured changes in various immune markers before, during, and after the session.
White Blood Cell Surge and Immune Surveillance
During the sauna session, researchers observed an increase in every type of circulating white blood cell measured. This included neutrophils and lymphocytes, which play critical roles in the body’s defense mechanisms. Neutrophils act as first responders to infection, while lymphocytes are responsible for recognizing specific threats and producing antibodies.
This phenomenon is linked to a process called immune surveillance. Normally, many immune cells reside in tissues rather than circulating freely. The heat stress from the sauna appears to push these cells into the bloodstream, where they can travel throughout the body. This increased circulation may help the immune system detect harmful bacteria and viruses more efficiently.
Ilkka Heinonen, an Academy Research Fellow at the University of Turku, noted that this periodic release of white blood cells is beneficial. He explained that once these cells leave their storage sites, they are better positioned to respond to pathogens. However, the study found that this surge was temporary. Within 30 minutes after the sauna session, neutrophil and lymphocyte counts returned to their baseline levels.
Cytokine Response and Temperature Links
The researchers also analyzed cytokines, small proteins that regulate inflammation and coordinate immune responses. Overall, the sauna session produced little change in average cytokine levels in the bloodstream. However, a closer look revealed a specific connection between certain cytokines and body temperature changes.
Jari Laukkanen, Professor at the University of Eastern Finland and lead author of the study, highlighted this distinction. He stated that the levels of several cytokines changed in relation to how much body temperature rose during the sauna bathing. No similar association was observed between white blood cell counts and changes in body temperature.
This difference suggests that sauna bathing influences different parts of the immune system through separate physiological processes. The response of cytokines to heat contrasts with the mobilization of white blood cells, which did not correlate directly with temperature spikes.
The study draws parallels between sauna bathing and physical exercise. Both activities can temporarily increase the number of immune cells moving through the bloodstream. While the mechanisms may differ, both practices appear to distribute immune cells more widely throughout the body. The researchers caution that this does not mean the two activities provide identical immune benefits.
The findings were published in the scientific journal Temperature. The authors note that the results do not establish whether sauna bathing produces lasting improvements in immune function or reduces the risk of illness. The study examined only the immediate effects of one session, and the observed changes were short-lived. Additionally, because the session included a cold shower, the findings reflect the combined routine rather than the isolated effects of heat alone.
Source: ScienceDaily
