That's far too optimistic. I can't find the full text of this dementia study, but the one where they concluded sauna improves cardiovascular health barely gives

That's far too optimistic. I can't find the full text of this dementia study, but the one where they concluded sauna improves cardiovascular health barely gives any thought to the idea that perhaps men with a worse subjective assessment of their health are more likely to find it unwise to go to sauna too frequently. (In the closing paragraph they do a disclaimer "It is possible that underlying diagnosed or undiagnosed diseases may affect saunabathing habits, but our subgroup analyses according to various clinical characteristics were consistent.")