I will start with a confession. While I know the benefits of hydotherapy - basically you take a hot shower for 30 seconds then switch to freezing cold for 30 seconds, then go back to hot and repeat for 2 or 3 minutes - it has never appealed to me. It may be fantastic for blood flow and good for your liver, but to me it seems brutal! So in the past, I have only spent a few short minutes in a sauna and I have never been tempted to jump into the ice cold plunge pool afterwards - despite my finnish friends telling me how fantastic it is.
So I was interested in the Kuopio Ischaemic Heart Disease Risk Factor Study which looked at if frequent use of a sauna has reduces the risk of high BP. The study looked at 1,621 middle-aged men living in eastern Finland. The study found that
Going to the sauna 4 to 7 times per week reduces your risk of develping High BP by 46%.
Going to the sauna 2 to 3 times per week reduces your risk of develpoing High BP by 24%.
So my Finnish friends who rave about going to the sauna are wise, going regularly helps to keep your BP in check.
F Zaccardi, T Laukkanen, P Willeit et al, Sauna Bathing and Incident Hypertension: A Prospective Cohort Study, American Journal of Hypertension, Volume 30, Issue 11, 1 November 2017, Pages 1120–1125, https://doi.org/10.1093/ajh/hpx102