Edit: as the comments said, I used the incorrect word. What I mean is “tolerance”
Approach with healthy skepticism. That page and its links to other studies are not enough to support its stated claims or implied benefits. https://sciencebasedmedicine.org/wim-hof-the-iceman/ does a better job than I can when it comes to the details. Looks like snake oil to me.
Oh, I wouldn’t ever suggest that the method does everything its author says it does - the claims of helping in cancer cases and such are wee bit too “optimistic”.
But the question was concerning the possibility to build up cold immunity. And the answer is “yes”. The method I mentioned absolutely will build up cold’s immunity (or resistance, or tolerance if language purism is a factor) in everyone who will attempt it.
There’s no magic hocus-pocus in it. It’s very simple concept used in many “methods” - Buteyko comes to mind, so does Russian Siberia.
Look into wim hof. He’s probably the best in the world.
Run 5ks at dawn in the winter and you’ll never feel cold again.
That never worked for me. I used to run in the early morning before dawn and if it was warm I could warm up and feel good. If it was cold (yes sometimes it gets cold even in Florida) I had to run wearing layers to be able to warm up enough to feel safe running. Sweatpants over yoga pants, tank, long sleeve running shirt, jacket.
I have seen people adapt to the heat here though, and my brothers who grew up in warm climate and moved to the northeast certainly adapted.
Trying to become an Aes Sedai?
I moved from a hot part of the world to a colder part. I’d say I’ve climatized and acclimated to the colder environment.
