Short read
Rhonda Patrick and Teresa Johnson published this review in Experimental Gerontology in 2021. It draws together observational, interventional and mechanistic studies and defines sauna use as brief passive heat exposure between 45 and 100 degrees, depending on the modality. Patrick is a co-founder of FoundMyFitness and discloses her role as a public communicator on the topic in the paper itself.
The review describes the mild hyperthermia of a session as a trigger for neuroendocrine, cardiovascular and cytoprotective mechanisms, and repeated exposure as a route to adaptation through hormesis. It reports that heat shock proteins increase in the first 30 minutes after heat exposure and remain elevated, a pattern the authors compare with the response to exercise. It also describes lower total and LDL cholesterol after a three-week sauna phase and an inflammation-regulating cytokine pattern similar to the one seen after training. The review has no comparison group of its own; these statements summarise the underlying studies.
It is a review and contains no new primary finding. Some of the primary studies it draws on are small. The lead author has a recognisable interest in spreading the topic, which is worth keeping in mind when reading its conclusions.
The value of the paper is conceptual. It describes heat not as relaxation but as a measured stress that the body answers with adaptation, and it places that answer close to the response to exercise. It does not show that sauna use extends healthspan in any individual, and the overlap with training is a description of mechanisms, not evidence that one can replace the other.