Someone I know sent me this. Here is my reply on 13 December 2025 covering the study, which I think is in the spirit of Seth’s post.
Thanks for sharing, [name]! To clarify, I was mostly sceptical about the ice bathing (I looked into this a bit because my father does 10 ºC bathing sometimes, and was claiming it has lots of benefits). I have now looked into the study above (“Sauna use as a lifestyle practice to extend healthspan”). I think the evidence presented there is very weak. In terms of data from interventional studies, which involve comparing a group which receives a treatment (like more sauna) with a control group, and are the type of study which offers the strongest evidence, they mention the following (I searched the paragraphs with “interv”):
“Findings from a small intervention study in rodents demonstrated that local heat application during an immobilization period decreased muscle atrophy by 37% compared to a sham treatment”. Very weak evidence because it is about rodents.
“A randomized controlled trial that examined the effects of sauna use in 24 patients with ischemic heart disease with chronic total coronary artery occlusion who had not responded to non-surgical procedures and had failed or were not candidates for percutaneous coronary intervention demonstrated that 15 waon sessions given over a 3-week period improved the patients’ vascular endothelial function as measured by flow-mediated dilation of the brachial artery. No significant improvements were observed in the control group that received standard medical care (Sobajima et al., 2013)”. Very weak evidence because:
The sample size is tiny (24 people in the treatment group).
The treated people are very special people (so sauna being beneficial for them does not imply it has benefits for a random healthy person).
They did not measure mortality (I do not know the extent to which this correlates well with “flow-mediated dilation of the brachial artery”).
“A small intervention study investigated the effects of repeat sauna use on endurance and other physiological effects in 6 male distance runners. The findings showed that one 30-minute sauna session twice a week for 3 weeks post-workout increased the time that it took for the study participants to run until exhaustion by 32% compared to their baseline”. Very weak evidence because:
The sample size really is super small (6 people)!
The treated people are not random people (they are distance runners).
They did not measure mortality (I do not know the extent to which this correlates with “time that it took for the study participants to run until exhaustion”).
“Another randomized controlled trial found that endurance training in a sauna suit led to improved performance and respiratory measures, including VO2max. The authors speculated that the improved performance time for the sauna suit group was due to improved VO2max and increased capacity for thermoregulation. For example, they noted that sweat rate during a heated 5 km time trial increased in the post-intervention group but not the control group (Van de Velde et al. 2017)”.
I am confused. The summary of this stufy does not even mention “sauna”.
In any case, I guess the same points about the study above apply. A “sauna suit” most likely implies a very small sample size, and they did not measure mortality.
“A small intervention study in humans found that daily heat treatments applied locally to muscle during 10 days of immobilization prevented the loss of mitochondrial function, increased HSP levels, and attenuated skeletal muscle atrophy by 37% compared to a sham treatment group (Hafen et al., 2019)”. Very weak evidence because:
They did not study realistic conditions. “This study investigated the effects of daily heat therapy on human skeletal muscle subjected to 10 days of immobilization”. The question is whether sauna helps random healthy people longterm, not whether they temporarily benefit people who were spending 10 days without moving.
This is not about sauna. It is about local heating. “daily 2-h heat treatment using pulsed shortwave diathermy”.
Someone I know sent me this. Here is my reply on 13 December 2025 covering the study, which I think is in the spirit of Seth’s post.