Reported by ScienceDaily
A single sauna session may trigger a surprising response in the immune system. Researchers in Finland have discovered that spending just 30 minutes in a sauna, with a brief cold shower halfway through, causes white blood cells to surge into the bloodstream. These cells are essential to the body's defenses, helping identify and fight infections and other potential threats.
The findings suggest that sauna bathing may temporarily mobilize immune cells that normally remain in tissues, allowing them to circulate more widely throughout the body. This increased movement could help the immune system monitor for harmful pathogens, including bacteria and viruses.
During the study, researchers observed an increase in every type of circulating white blood cell they measured. Among them were neutrophils and lymphocytes, two important groups of immune cells. Neutrophils are often among the first defenders to respond to an infection, while lymphocytes include cells that recognize specific threats, produce antibodies, and help coordinate immune responses.
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The increase was temporary. Within 30 minutes after the sauna session, neutrophil and lymphocyte counts had returned to their original levels.
"This may indicate that sauna bathing mobilizes additional white blood cells into the bloodstream from tissues, where they are then redeposited after the session. This kind of periodic release of white blood cells into the bloodstream is beneficial, as once they leave their storage sites, they are better able to patrol the body and respond to pathogens," says Ilkka Heinonen, an Academy Research Fellow at the University of Turku.
This process is known as immune surveillance. Rather than remaining in one location, immune cells travel through the bloodstream and tissues, searching for signs of infection or other abnormalities. By temporarily increasing the number of white blood cells in circulation, the body may improve their ability to detect potential threats.
Interestingly, a similar response occurs during physical exercise. Exercise can temporarily increase the number of immune cells moving through the bloodstream, helping distribute them throughout the body. The new findings suggest that sauna bathing may produce a comparable short-term response, although this does not mean the two activities provide identical immune benefits.
The researchers…