Sauna study: one session briefly raises white blood cell counts

A single sauna session briefly sets the immune system in motion, according to researchers from the University of Eastern Finland and the University of Turku writing in the journal Temperature. In the study led by Professor Jari Laukkanen, 51 adults with an average age of around 50 spent 30 minutes in a Finnish sauna, interrupted by a short cold shower. Before and after the session, their blood was tested for white blood cells and cytokines – signalling molecules that immune cells use to communicate. The science portal ScienceDaily reported the findings on 28 October.

After the session, the number of every type of white blood cell measured had risen, including neutrophils and lymphocytes. Within 30 minutes, however, the counts returned to baseline. Cytokine levels changed little on average, although some varied with how much body temperature rose. Researcher Ilkka Heinonen of the University of Turku said this may indicate that sauna bathing mobilises additional white blood cells from tissues into the bloodstream. That is a proposed explanation, not proof.

The researchers see parallels with the immune response to exercise but stress that the two need not bring the same benefits. Only a single session and its immediate effects were studied. Whether regular sauna use protects against infections or improves long-term health cannot be concluded from the results. Because the session included a cold shower, the findings also reflect the combination of heat and cooling rather than the effect of heat alone.