Jet Lag - The Science

From a NYTimes blog:

Jet lag comes courtesy of a disruption in your body’s internal clocks, a condition known as circadian desynchronization. Nearly every living creature has a circadian system whose rhythms control the timing of many aspects of biochemistry, physiology and behavior. For instance, virtually all our hormones oscillate with a 24-hour rhythm...[the source of which are] the suprachiasmatic nuclei (SCN) in the anterior hypothalamus of the brain. The SCN neurones individually are capable of generating near-24-hour oscillations in electrical activity and, collectively, they produce the master rhythm that essentially controls the animal’s crucial rest-activity cycle.

The SCN-generated rhythm is aligned to the daily solar cycle of 24 hours by the photic signals of sunrise and sunset via a light-sensing pigment called melanopsin, found in special cells located in the retina of the eye.
...About one-fifth of liver enzymes show circadian rhythms...This means that the metabolic capabilities of the liver change dramatically between day and night as different groups of enzymes are turned on and off...left to their own devices, the liver’s clocks can fall out of sync with the clocks in other tissues. The SCN signals inform the peripheral cells to adjust the phase of their rhythms, like the pin of a wrist watch being moved a little bit forward or backward.

If we think of the circadian system as an orchestra, then the SCN, synchronized to the external world by the light signals, acts like the conductor, beating out a rhythm that coordinates the multiple rhythmic parts of the body. When the orchestra is in time we get a melody; when it is not there is a cacophony. The same thing happens in our bodies, though how this is done is not at all clear and is the subject of intensive study.

Crossing time zones in a jet plane decouples these rhythms from the natural day-night cycle...On a long trip, the various rhythms fall out of sync and your stomach ends up over Peking, your liver somewhere near Delhi, while your heart is still in San Francisco. Metaphorically speaking, of course.

...Altering the lighting schedules...Maybe the answer is to develop two pills. One would inhibit jet lag symptoms and would be available to all essential long-haul fliers like pilots and, say, academics attending conferences. Non-essential long-haul travelers would have to take another pill, which would intensify the effects of jet lag. They could still fly if they wanted to, but most would not and we essential travelers would, at last, be able to stretch out in comfort.