DANIEL WAGNER, MD: Oh, it's a very real problem. And it's due to the fact that we have an internal clock that tends to get set to the time zone we live in every morning and most people's clocks do a pretty good job of that. But, the clock was not designed to suddenly go across the country or across the ocean on a jet plane. It evolved over millions of years to basically, pretty much stay in the same place from day-to-day. And so it has a limited flexibility as to how it can time our internal functions in concert with the external world. It's the light-dark cycle of the external that does the retiming and synchronizes our internal clock to the outside world.
And so when you suddenly zip over to another time zone and there's a different light-dark cycle, your clock is still set to the home. And because of that it tries to make your body function, to sleep and wake at the times like home. But you're not at that time any more. And it takes about an hour per time zone for your clock to catch up to the new time zone.
Because of that, people very often have trouble sleeping at the new time. Particularly, trouble waking up a lot in the second half of the night. And then they're tired and sleepy in the daytime -- both because of that insomnia, but also because their body clock is still on, let's say, New York time when they're in Hawaii. And when you're supposed to falling asleep -- New York time, let's say it's 11 o'clock -- it's only about 5 o'clock in the afternoon in Hawaii.
DAVID FOLK THOMAS: But at least you're in Hawaii. Dr. Zak, can you elaborate more on the light-dark thing that Dr. Wagner was just mentioning?
