A new study in mice suggests an unlikely cure for jet lag: oxygen deprivation.
When the animals breathed air with about one-quarter to one-third less oxygen than usual, they adapted to a six-hour time change more rapidly than mice that breathed regular air, according to a report published Thursday in the journal Cell Metabolism.
Oxygen is essential to humans, mice and other animals. The cells in our bodies need oxygen to convert carbohydrates into energy. That's why we breathe it in all the time.
A team of researchers from the Weizmann Institute of Science in Israel and the University of Bristol in England suspected oxygen might be useful for another reason as well — keeping our circadian systems in sync.
[Researchers explain why jet lag can be worse when you travel east]
The circadian system makes sure that all of the body's cells are in tune with our master internal clock. Our daily cycle of eating and fasting helps with this. So does our body temperature, which falls in the hours before we go to sleep, then rises as we prepare to wake up.
The researchers realized that both eating and temperature regulation are "tightly linked to oxygen consumption," they wrote.
To learn more about oxygen's role in regulating circadian rhythm, the scientists monitored oxygen levels in the blood and tissues of mice. Sure enough, they found that the mice consumed more oxygen when they were exposed to darkness (this is their active phase, since they are nocturnal) and consumed less oxygen when exposed to light (when they rest).
Next, they conducted experiments with mouse cells cultured in laboratory dishes. The cells were exposed to varying amounts of oxygen, and researchers checked to see which genes were expressed.
Some of the dishes were put on a cycle that had them toggling between 8 percent oxygen and 5 percent oxygen over a 24-hour period. Others lived exclusively in an 8 percent oxygen environment. The researchers found that the cells exposed to varying levels of oxygen became synchronized to a new rhythm.
In a final step, the team got mice habituated to a cycle of 12 hours of light and 12 hours of dark. Then they made a one-time adjustment that sped up the schedule by six hours, mimicking the effects of jet lag. The difference was the equivalent of flying from Chicago to London.
The mice normally breathed air with 21 percent oxygen (just as people do in the real world). But for 12 hours before the "clock" was shifted forward, some of the mice got only 16 percent oxygen. These mice adapted to the new lighting schedule "considerably" faster than their counterparts, as judged by their eating, running and sleeping, the researchers reported.
The team also tested a scenario that dialed back the oxygen to a mere 14 percent, though only for two hours. This "short pulse" of oxygen deprivation was enough to help mice get over their "jet lag" more quickly, according to the study.
It remains to be seen whether the same approach would work for humans, who (unlike mice) actually have to cope with jet lag. The researchers argue that it's worth figuring out — especially since it's possible for airlines to increase the amount of oxygen in the passenger cabin of certain planes.
The air in a typical airplane cabin contains about 16 percent oxygen, roughly the same oxygen content as a city that's up to 8,000 feet above sea level. But this reduced amount of oxygen makes some passengers feel airsick. The new Boeing 787 Dreamliner, for instance, makes it possible for airlines to increase the cabin pressure by pumping in more oxygen.
Although it might make passengers more comfortable while they're in the air, the extra oxygen could make them more miserable once they're back on the ground.
"The aviation industry is investing substantial funds and efforts to improve and increase the cabin oxygen levels to 21 percent O2," the study authors wrote. "This should be reconsidered in view of the beneficial effect of reduced oxygen levels in jet lag recovery that are reported here."