A disturbance or difficulty in adjusting our internal clock to new location as a result of travelling when we across several time zones.

Persons suffering from jet lag feel tired, dull and generally out of sorts.Research on circadian rhythms indicates that it is easier to reset our biological clocks by delaying them than by advancing them. In other words ,we experience less disruption when we fly to a time zone where it is easier than the one in which we normally live, than when we fly to one where it is later.For instance, if you live on the East Coast of the United states and fly to California , where it is three hours earlier you stay up a few extra hours, and then go to sleep.

In contrast if you live in California and fly to the Est Coast where it is three hours later, you may experience greater disruption and take longer to adjust your internal clock.


Light acts as a zeitgeber , resetting our biological clock.If you travel from New York to Paris, starting out in the evening(most flights depart at that time)you fly into darkness, but then just when you are really tired and about to fall asleep, dawn occurs, and the cabin is filled with brilliant sunlight. Your SCN (Super ChiasmaticĀ  nucleus) responds, and resets your biological clock to morning.But you in haven’t had a night’s sleep.

You aren’t really prepared for the start of a new day.As a result you feel awful, it may take you several days to get back to normal.If you fly to the west, you leave in daylight and arrive in daylight, so you don’t experience the same unsettling effects. You “gain” several hours and just stay up a little longer than usual.


An environmental agent or event that provides the cue for setting or resetting a biological clock.


Zeitgebers and Jet Lag : When Dawn Comes too Early!


Passengers flying across several time zones to the east(e.g. from New York to Paris or London) often startĀ  theirĀ  journey in the evening . Just when their biological clocks are signaling” Time to sleep”, the plane flies into a new dawn.The bright light acts as a Zeitgeber, resetting their biological clocks and contributing to their fatigue.



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