20 minutes in a 174°F sauna, four times a week, drops all-cause mortality by 40%. Jari Laukkanen tracked 2,315 Finnish men for 20 years. Compared to once-a-week users, the 4-7 sessions per week group had 50% lower fatal cardiovascular disease, 63% lower sudden cardiac death, and 65% lower Alzheimer's risk. Same cohort. Same age range. The variable was sauna frequency. The mechanism is heat shock proteins, and a new 52-page review in Comprehensive Physiology just compiled the evidence. When…