I have read on a lot of forums that
under eye circles can be caused by dehydration, malnutrition,
vitamin deficiencies, sleep deprivation, etc.
For the record, I would like to say that I drink quite a bit of water daily and eat pretty good, I hardly eat out and I take a centrum multivitamin each day. I also workout about 5 times a week doing a little bit of something whether its running, pushups etc.