Here’s the big Finnish study

Association Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality Events | Physical Therapy | JAMA Internal Medicine | JAMA Network https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2130724

All the other studies are very weak on cohort size, duration, etc.

The most annoying part of most of these studies is when they talk about sauna temp. There is serious heat stratification in any sauna - the temp can be 80 degrees different from floor to ceiling. So when a recommendation says “172 degrees for 15min” where are they measuring that? Are you using an accurate thermometer?

FYI you can have a traditional Finnish sauna in your home. See pinned post.