I have just attended the A5M The Australasian Academy of Anti-Ageing Medicine conference and am re-invigorated, bringing back information on extreme wellness.

e.g. Cold showers – This is thought to increase the number of mitochondria (energy factories) in the cells.

For those wanting to know more, the renowned Prof Marc Cohen was one of the excellent speakers exploring mitochondrial health and regeneration. 
https://drmarc.co/