Dr. Peter Attia just posted a podcast about hot and cold therapy. Unfortunately it is one of the teasers he has named AMA (ask me anything), that is used to get you to signup and you only get to hear part of it unless you are a subscriber. This tipped me over the edge and I signed up. I have listen to all of his podcasts and, I figured I owe it to him to help with continued research.
The information below is only related to life extension.
The gist of the literature on cold therapy, ( cryogenics, ice bath) is not useful for life extension, it is useful for delayed onset muscle soreness, after 24 to 72 hours.
There are many papers with evidence that sauna use is a life extender.
The term used is "reduction of all caused mortality" The data says at least 177* for 20 minutes, 4 times a week. It is compared to exercise in it's efficacy.
Here's the hot/cold podcast.
https://peterattiamd.com/ama16/Dr. Attia quote, "It's hard to look at these data and not think there is something going on here, not withstanding all of the limitations you have eloquently described. I'm struggling to see a scenario now that robust* use of sauna... it really seems that there are benefits of doing that."
For all of Dr, Attia's podcasts, page down to recent podcasts.
https://peterattiamd.com/podcast/* robust, meaning 4 days a week, 177*F for 20 minutes.