Short read
Kunutsor, Laukkanen and Laukkanen studied a random sample of the general Finnish population, women and men, in a prospective cohort study published in Neurology in 2018. It was the first prospective analysis of sauna use and stroke that included both sexes. Several sensitivity analyses were built in to guard against reverse causality.
Compared with less frequent sauna use, frequent use was associated with a markedly lower risk of stroke. The authors also ran the analysis with a combined reference group of non-users and people who went once a week. The size of the difference is quoted in secondary sources but has not yet been checked against the original paper, so no figure is given here. The association held when the first two years of follow-up were excluded, and when people with pre-existing disease were excluded.
In an accompanying letter in Neurology, the German neurologist J. G. Heckmann pointed out the usual limits. The data cover the Finnish dry sauna at around 80 degrees, not infrared cabins at about 60 degrees. The design is observational, and sauna habits may have changed over the years.
The authors discuss lower blood pressure, reduced arterial stiffness, improved endothelial function and dampened systemic inflammation as possible mechanisms. The study extends the cardiovascular findings to cerebrovascular events. It describes a relative difference within one population and does not show that sauna use prevents a stroke in an individual.