PETER HACKETT: There's evidence that the people who do best at altitude are dehydrated. That is the body resets the serum of molality level which has to do with the water balance. And the body, for some reason, prefers to be dry at high altitude. My own thinking is that this is good for the body because it keeps the brain a little bit drier and softer. So that if it does start to accumulate a little water or get a little swelling, it can be tolerated better.
I wonder if that has anything to do with the fact that I have never experienced any symptoms of altitude sickness aside from loss of appetite. I do know I am usually dehydrated when I am hiking and climbing (I rarely urinate and when I do it is deep orange).