Wim Hof's breathing method is acclaimed to improve physical and mental health by following the following routine once every day:
- 30 deep, strong breaths
- breath-hold after exhalation for as long as comfortable (it's not comparable to normal breath-holding under water as the preceding hyperventilation phase makes one not have the urge to breathe for quite some time)
- deep inhalation followed by another breath-hold for 15 sec.
- repeat steps 1-3 another 2-3 times
Studies have already shown that this method profoundly impacts the body. An author of this platform summarized it in a question briefly. I also found this online post quite interesting (jump to "Wim Hof Breathing Explained"). However, I couldn't find any research about the long-term effects or any well-founded claims about the potential detriments this breathing method has on the body (as long as one is healthy and follows protocol).
According to a user on Quora, free-diving record holder William Winram claims that this self-induced hyperventilation promotes the release of free radicals that result in cell damage. A consequence is an accelerated aging process of the body.
But is that claim well-founded? According to this author, the breathing method "involves a hyperventilation phase in preparation of a hypoventilation phase" and thus claims that there are no damages associated with hyperventilation, unless you overdo this practice.