How does circadian adaptation typically occur when traveling?

Circadian adaptation, which is the process by which the body's internal clock aligns with the external environment, is influenced significantly by the direction of travel. When traveling east, a person generally faces a greater challenge because they are effectively losing time—meaning the day becomes shorter as they cross time zones. The human circadian rhythm is naturally set to a roughly 24-hour cycle, and adjusting to a shorter-day scenario is more difficult than adjusting to a longer one.

The body's internal processes, including hormonal release and sleep-wake cycles, respond more favorably to extending day length rather than shortening it. Therefore, traveling eastwards can create a mismatch between the internal clock and the external light signals, requiring a longer period for adaptation. In contrast, traveling west typically allows for a more gradual adjustment since the day is getting longer, making it easier for the body to adapt.

This understanding highlights why adaptation is more effective when traveling west compared to east. Moreover, adaptation does not occur uniformly in all directions or instantaneously; it involves both behavioral adjustments and physiological changes, and it can take time to align fully with local time, especially when traveling east.