The way the human circadian clock sets itself may explain why jet lag tends to affect people more severely when they're flying west to east compared to the other direction, a new animal study indicates.

The circadian clock, which regulates many body processes, has to make regular adjustments to stay synchronized with the light-dark cycle of where a person is and does this by delaying or advancing its time in response to light.

Typically, these adjustments occur without notice. However, the process is disrupted by sudden major changes in the light-dark cycle, such as when a person takes a long flight.

Previous research found that delaying and advancing the circadian clock occur in different pathways in an area of the brain called the suprachiasmatic nucleus. This new study found that the molecular mechanisms in these pathways are significantly different.

Advances more difficult

"We have known for decades that, in humans and other organisms, advances are always much harder to achieve than delays. For example, compare jet lag going to Europe with that coming back," Horacio de la Iglesia, an associate professor of biology at the University of Washington, said in a university news release.

"One of the reasons may be that these two forms of resetting the clock involve different molecular mechanisms at the clock level," he suggested.

The findings from experiments with hamsters could help in efforts to develop remedies to jet lag, according to the researchers.

The study was published online in Proceedings of the National Academy of Sciences.

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