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By Stephen Beech
Taking a sauna boosts the immune system, reveals new research.
Sauna bathing releases white blood cells into the bloodstream, according to the findings.
Circulating white blood cells play a "key" role in the body's defense against viruses, bacteria, fungi and diseases, say scientists.
Previous research has shown that regular sauna bathing has been associated with several beneficial health effects.
The new findings may, in part, help explain how those effects develop in the body.
The Finnish study involved 51 adults with an average age of 50.
The findings, published in the journal Temperature, showed that a 30-minute sauna session, with a brief cooling period under a cold shower midway through, increased the number of all circulating white blood cells.
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Neutrophils and lymphocytes, which are central to immune defense, returned to original levels within 30 minutes.
Ilkka Heinonen, an academy research fellow at the University of Turku, said: "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,"
He says the release of white blood cells into the bloodstream, which also occurs during physical exercise, is the body's way of enhancing immune surveillance by white blood cells throughout the body, and boosting its immune defense.
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As well as immune cells, the research team also measured the levels of numerous cytokines, which act as mediators in immune defense.
On average, sauna bathing had little effect on circulating cytokine levels.
Study leader Jari Laukkanen, from the University of Eastern Finland, said: "Interestingly, however, the levels of several cytokines changed in relation to how much body temperature rose during sauna bathing."
He added: "No similar association was observed between white blood cell counts and changes in body temperature,"
The research team said the study was limited to a single sauna session and its immediate effects, so no definite conclusions can be drawn about longer-term health effects.
