Everyone who has travelled in an airplane is familiar with jet lag. True, the effect only applies when travelling east or west. But jet lag is so pervasive and annoying—not to mention a safety risk for pilots—that it merits serious discussion.
Jet Lag Defined
Technically, jet lag is known as circadian desynchrony. At its core, the condition results from the fact that it takes our body more time to adjust its internal clock to a new time zone than it does to fly there.
This internal clock is located in a region of the brain called the suprachiasmatic nucleus. It governs many important processes in the body, including the release cycle of hormones such as somatotropin (human growth hormone), cortisol (stress hormone), and melatonin (sleep hormone). And just like a normal clock, the internal body clock has its own process for “setting the time.” The mechanism is based on natural daylight.
When photosensitive retinal ganglion cells in the eyes collect information about ambient light patterns, the brain interprets this information and executes a shift in the phase of the circadian rhythm (see Figure 1). In normal conditions—that is, in the absence of any air travel across time zones—the shift is small and imperceptible.
Think of it like the daily adjustment you might make to an heirloom grandfather clock that runs slightly slow. In abnormal conditions (relative to our biology), the pattern of day and night of our destination time zone is significantly mismatched from that of our existing circadian rhythm. The circadian rhythm has become “desynchronized.” Mathematically speaking, the phase of the body clock is shifted relative to the phase of the diurnal daylight cycle of the new time zone. This phase shift is the familiar feeling of jet lag.
Jet Lag Illustrated
Jet lag is illustrated by the gray arrow in the figure below (Figure 2). The blue cycle represents the day/night rhythm of the new time zone, as well as the circadian rhythms of the local,…