How strong is the evidence for Sauna?

A well-known Finnish cohort study (KIHD) found frequent sauna bathing (4-7 times per week) was associated with substantially lower fatal cardiovascular and all-cause mortality compared with once weekly, a finding extended by related analyses from the same cohort linking sauna use, cardiorespiratory fitness, and reduced risk of sudden cardiac death. That evidence is currently rated moderate (72/100), built on 8 published studies, including 2 meta-analyses -- a reasonable base, but not yet enough for full certainty.