To date, these effects have been documented only in jet-lagged subjects, not after recovery from jet lag, Gibson said. The UC Berkeley study is the first to look at long-term effects as well as changes in brain anatomy.

"The evidence is overwhelming that disruptions in circadian timing have a direct impact on human health and disease," Kriegsfeld said. "We've now shown that the effects are long-lasting, not only to brain function, but likely to brain structure."

The researchers used hamsters in their study because they are a classic model of circadian rhythms. Their bodily rhythms are so precise, Kriegsfeld said, that they will produce eggs, or ovulate, every 96 hours to within a window of a few minutes.

Because jet lag can increase stress hormones like cortisol and disrupt reproduction, the researchers controlled for the effects of these by removing adrenal glands or ovaries in some of the hamsters and injecting normal levels of hormone supplements of corticosterone and estrogen, respectively. These hamsters showed a similar reduction in new, mature hippocampal neurons in the brain.

"The change was really dramatic and shows that the effect on behavior and the brain is direct, not a secondary effect of increased stress hormones," Gibson said. "They are not due to increased cortisol concentrations."

The experiments also suggest that the low number of mature neurons in the hippocampus in jet-lagged hamsters was not due to decreased production of new cells, but rather, fewer new cells maturing into working cells, or perhaps new cells dying prematurely. Further studies are planned to determine the root cause of the reduction in mature neurons.

How do you avoid jet lag problems? Kriegsfeld said that, in general, people should allow one day of recovery for every one-hour time zone shift. Those, such as night-shift workers, who cannot return to a normal day-night cycle should sleep in a room with light-tight curtains shielded from outside noise in order to properly adjust to an altered sleep schedule.

Source: University of California - Berkeley