Do you really think that the people who worked on this study didn't consider your knee-jerk level-1 confounding factor? Obviously they look socioeconomic status into account when they were studying all-cause mortality, what study wouldn't?
There is a reproducibility crisis in many fields where people tacitly assumed everyone else was doing their due diligence. Many basic assumptions about confounding factors, confidence values, etc are still being criticized and revisited. You should not assume that such factors have been accounted for, instead you should join in continually asking if they have been and challenging all assumptions.
I'm not making that assumption, I'm asking what factors they included. Lots of studies are poorly run and fail to account for very simple confounding factors.
The big study was a 20+ year observational study in Finland [1] where Sauna's are supposed to be quite accessible, but the world is complicated and there are probably many confounding factors.
The mechanism of action seems very plausible. Sauna's are moderate stress which spikes your heart rate temporarily (they say 100-150bpm in the study). So it's not surprising it could be protective for cardiovascular disease just like many other forms of moderate stress/exercise.
I don’t mind people asking obvious questions. Even if the answer is also obvious, it’s still an important base to cover, and we shouldn’t assume it was. The humanities is replete with flawed studies.
