When we travel long-distance and trans-meridian (east–west or west–east, time zones) on high-speed aircraft we may experience jet lag. jet lag was uncommon before the arrival of passenger jet aircraft. Travel by ship or by train were too slow and of more limited distance than jet flights, and thus did not contribute to the problem.
When travelling across a number of time zones, the body clock will be out of synchronisation with the destination time which can couse you up for several nights after you land and disrupts your daily routine.
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We might not be aware of our internal “body clocks” until we are jetlagged, but scientists continue to puzzle over what drives them. Now, an Israeli study has found that changes in surrounding oxygen levels can reset circadian clocks of mice. If confirmed in humans, the research could help inform how airlines moderate cabin air pressure.
According to a report published Thursday in the journal Cell Metabolism, many biological processes follow a set timetable, with levels of activity rising and falling at certain times of the day.
Such fluctuations, known as circadian rhythms, are driven by biological “clocks” based on an approximately 24-hour period.
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, ” as 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. 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).
Dr. Gad Asher of the Weizmann Institute of Science’s Biomolecular Sciences Department and his colleagues, showed that changing the concentration of oxygen in cells by just three percent, twice a day, will reset mouse cells’ circadian clocks.
“It was extremely exciting to see that even small changes in oxygen levels were sufficient to efficiently reset the circadian clock, ” says Asher. “The study actually raises a lot of important questions.”
The researchers further explored oxygen’s effect on circadian rhythms with jetlag experiments. Just like humans, mice are prone to jetlag after a sudden shift in daylight hours. Mice were left to eat, sleep and run on their wheels in oxygen-controlled environments. Altering oxygen levels during their normal sleep-wake cycle did not change their circadian rhythms, but once mice experienced a six-hour jump ahead in daylight hours, varying oxygen levels could help them adapt their eating, sleeping and running habits to the new time faster.
For example, the scientists saw that a small drop in oxygen levels 12 hours prior to the six-hour daylight shift, or two hours afterwards, put the mice back on their circadian schedules faster.
Presently, commercial airliners pressurize cabins to the same air density of a city 6, 000-8, 000 feet above sea level. This low-pressure saves wear and tear on the airplane, but enough passengers suffer from airsickness in response to this drop in oxygen levels that some airlines are considering ways to increase the pressure on flights. In fact, Boeing designed its new 787 Dreamliner so that it can be pressurized to the equivalent of lower altitudes for this reason. But in light of these findings, the researchers note that although passengers may feel better with higher pressurized cabins during flights, they may lose the potential advantage of recovering from jetlag. The researchers now want to test how higher oxygen levels may affect the circadian clock.
“I believe passengers might be more enthusiastic to inhale oxygen-enriched air to alleviate jetlag in contrast to low oxygen, ” said Asher.
Understanding how oxygen influences the circadian clock goes beyond jetlag. Cardiovascular disease, COPD, shift work sleep disorder and other common health problems can result in tissues with low oxygen levels.
“We show that oxygen works in mammals, specifically rodents, but it will be interesting to test whether oxygen can reset the clock of bacteria, plants, flies and additional organisms, ” says Asher.
