A hot issue

Hmm.  A study from Finland finds that frequent sauna use by folk over 50 is associated with (much lower) mortality from cardio vascular disease.  But is it just that healthy people tend to have more sauna time, or is there causation involved?   A doctor thinks it the sauna might make people fitter:

Professor Laukkanen continued: "There are several possible reasons why sauna use may decrease the risk of death due to CVD. Our research team has shown in previous studies that high sauna use is associated with lower blood pressure. Additionally, sauna use is known to trigger an increase in heart rate equal to that seen in low to moderate intensity physical exercise."

I wonder:  the Japanese have long lives too, and really like their hot baths.   Possible causation there too?

Well, there you go - this has been the subject of specific study too:

 The objective of this study was to determine how traditional Japanese style bathing could promote good health. Using healthy volunteers, we assessed body temperature (core and cutaneous), red blood cells, white blood cells (WBCs), venous blood gas parameters (PO2, SO2, PCO2, TCO2, HCO3, and pH), weight loss (which may indicate sweat volume), and the time until sweating before and after bathing. We simultaneously conducted a double-blind clinical trial using a bath additive group and a control group to investigate the effect of a bath additive on the same parameters. We found that bathing increased the core and cutaneous body temperature, as well as PO2, SO2, and blood pH. All of the subjects also showed increases in heart rate and weight loss (sweat volume). After bathing, the number and ratio of granulocytes increased while the number and ratio of lymphocytes decreased. These results tended to be emphasized in the bath additive group; however, significant between-group differences were not detected. Our results indicated that bathing improved blood circulation and had a modulatory effect on the autonomic nervous system. This suggested that traditional Japanese style bathing might contribute to good health and longevity; however, additional larger-scale studies were needed to confirm or refute this conclusion.