What Causes Jet Lag: Internal Clock Slow to Change Time

Jet lag is never a fun experience. You feel exhausted and sluggish as your body attempts to adjust to its surroundings. Now, scientists have discovered exactly why that is. Using mice, they've revealed why the body is so slow to recover from jet lag and have identified a target for the development of drugs that could help us adjust to faster changes in time zones.

Nearly all life on Earth has an internal circadian body clock that keeps us ticking on a 24-hour cycle. This clock synchronizes bodily functions, such as sleeping and eating, with the cycle of light and dark in a solar day. When we travel to a different time zone, though, our body clock doesn't adjust to the local time instantly. Instead, it can take up to one day for every hour the clock is shifted, which can result in several days of fatigue.

In order to investigate this internal clock, the researchers took a look at the region of the brain that drives the circadian clock in mammals called the suprachiasmatic nuclei (SCN). This brain region essentially pulls every cell in the body into the same biological rhythm. More specifically, the scientists used mice to examine the patterns of gene expression in the SCN following a pulse of light during the hours of darkness. In the end, they identified around 100 genes that were switched on in response to the light. Among these, they identified the molecule SIK1, which acts as a brake to limit the effects of light on the clock.

"We've identified a system that actively prevents the body clock from readjusting," said Stuart Peirson, one of the researchers, in a news release. "If you think about, it makes sense to have a buffering mechanism in place to provide some stability to the clock. The clock needs to be sure that it is getting a reliable signal, and if the signal occurs at the same time over several days it probably has biological relevance. But it is the same buffering mechanism that slows down our ability to adjust to a new time zone and causes jet lag."

The findings reveal a little bit more about how our internal clocks function. In addition, the research could pave the way for drugs that could bring bodies in tune with the solar cycle more quickly. These drugs also might have broader therapeutic value for patients with mental health issues.

The findings are published in the journal Cell.