When we take a flight across time zones, our circadian timing system has no knowledge of the shift to a new light-dark cycle, so it stays at home base, and adjusts only gradually. On landing, the inner clock may be set to night, even if it is midday outdoors. The conflict produces jet lag, with a host of psychological and physical symptoms that can seriously disrupt one’s trip.
Management of jet lag has taken two forms:
- Proactive: beginning to reset in the inner clock toward the day-night cycle of the travel destination before the trip starts.
- Retroactive: taking measures after arrival to expedite the clock-shift to the destination.
Tools to smooth the time shift include: timed light therapy; timed light exposure outdoors; use of protective eyewear when outdoors in the light during the circadian night; darkening the bedroom if there is daylight during the circadian night; and timed melatonin tablets to expedite the clock’s shift into nighttime mode.
Because of the complexity of these maneuvers, they are often difficult to follow, and success can be elusive. There are other complications to jet lag, including travel stress, and adoption of a daily routine that markedly contrasts with home-based habits.