During the pandemic, many people have barely left their neighborhoods, let alone their own time zone. But the vaccines are available, cabin fever is raging and the holiday season is upon us. And so, inevitably, the jet lag.
The human internal timing device, known scientifically as the circadian clock, is a powerful force. It synchronizes functions between organs and tissues and affects cognitive functions, digestion, sleep, and even asthma. Adjusting the circadian clock to a new time zone or time is not as simple as resetting a wristwatch, but current research into how to manipulate it can be useful for anyone, whether they are at their in-laws or on Mars. .
“There are so many promises to come, now that we understand the molecular power of the clock, to harness the power of the clock for good,” says Carrie Partch, professor of biochemistry at UC Santa Cruz who studies the circadian system. She says the more we understand the clock, the more freedom we will have, because we can make it an ally rather than an enemy.
Throughout the body, cells have their own circadian clocks that regulate metabolism and other cellular functions. These clocks coordinate between other cells in specific organs and even between organs, although scientists are still trying to figure out how they do it. All of these individual clocks are regulated and synchronized by the suprachiasmatic nucleus of the brain, a “stimulator” part of the hypothalamus that is very sensitive to external stimuli, especially light and dark. Light signals it’s time to wake up and be alert, while darkness means it’s time to slow down and sleep.
Although these signals are closely related to the sleep cycle, they have downstream effects on a multitude of biological functions. “I think of the circadian pacemaker as the conductor,” says Erin Flynn-Evans, who heads the Fatigue Control Lab at NASA’s Ames Research Center. “It controls a whole host of biological functions. There are circadian clocks in the liver, in the gut, in reproductive hormones. The primary pacemaker of the suprachiasmatic nucleus sort of synchronizes the timing of all of this biological function. “
But that internal timekeeper can’t always keep up with human behavior. When travelers cross time zones quickly, the circadian clock becomes out of sync with the outside world, an experience most people call jet lag. This mismatch can cause a range of symptoms including fatigue and sadness, sleeplessness and even digestive issues.
For most people, this is a relatively rare occurrence and just an inconvenience. But for workers like pilots and flight attendants, who can experience these changes on a daily basis, jet lag can affect their long-term health. Even relatively short jumps affect cognitive function. One 2017 study published by researchers at Northwestern University found that professional baseball players who traveled only two or three time zones for a game performed worse. The same problems exist for shift workers like nurses and people with irregular schedules like long-haul truck drivers, who work schedules that prevent them from sleeping at night.