[ploxolo]

Not sure, seems like the ones that did it already were self-determined enough to work. You would need to compare intra group before and after.

From a metabolic viewpoint cold showers might have some short term energy boost from the stress hormones it releases. However highly dubious whether that is healthy or sustainable long-term. 10-years down the line my bet is you would look like a marathon runner, all wrinkled and with bad skin. Hot showers can increase prolactin so I guess, moderation in both would be the way to go.