Yes, this seems very common as low as 9,000 feet. I often see edema. People note it and ask about it. Seems benign -- that is, no obvious relationship to that and HAPE or HACE (though, at some level, it must be a similar mechanism...). For people acclimating normally, it goes away by day 3 at altitude.
Perhaps some MD could explain it better, but there's something going on with fluid in tissues. I notice (even in myself) that it builds up slightly in hands and feet, then after a couple of days, you piss a lot and everything's back to normal.
I rarely have symptoms of AMS (headache, nausea etc.). But a day or two of increased urinary frequency does happen (OK. Perhaps too much detail, but there you go...).
George
