The idea of jet lag, or how impossible it feels to adjust to a new time zone when you travel, seems to have been coined in the 1960s in the Los Angeles Times, when a writer warned that "Jet Lag derives from the simple fact that jets travel so fast they leave your body rhythms behind." In the ensuing decades, we've understood a lot more about how jet lag itself works, and people who take long-haul flights regularly can rejoice: we're getting closer to knowing how to cure it.
The basis of jet lag is in the body's approach to sleep and wakefulness. Humans, like other mammals, have internal circadian rhythms that govern when they feel sleepy and wake up; they make up what we call a "body clock," and involve complex shifts in the body's hormonal levels, temperature and other factors over a 24-hour period. And while you can affect these by getting more sunlight and other factors, they're mostly determined by the clocks contained in your cells — which is bad news for international travelers. Humans haven't evolved to be able to shift their circadian rhythms to adjust to the swift travel of today's technology. People with jet lag end up in a place where the weather and daylight are telling them one set of time cues and their cells are telling them another, and jet lag is the process of adjustment — which is typically pretty awful and involves a lot of waking up at 4 a.m.
How long it takes to recover from jet lag is a contentious point. According to research from 2016, recovery rates depend both on how many time zones you've crossed and in which direction you happen to have travelled. People who've caught a plane going west will take six days to recover from six time zones, and up to nine days for crossing 12. People going east, however, need eight days for just six time zones. The directional nature affects jet lag because the circadian rhythms of the body aren't perfectly day-length; they're more like 24.5 hours long. And flying westward lengthens days, while flying eastward shortens them, meaning more impact on the body's adjustment period.
But there may be more hope in the future for people who suffer severely from jet lag's woes. Melatonin, a hormone produced in the brain, is available in some countries, including the U.S., as a nutritional supplement that's meant to help sleep, and is thought to be potentially helpful to adjust sleep cycles, though it remains controversial. More sophisticated methods beyond taking pills, though, are also being tested. According to research from 2017, cells present in your eyeballs produce vasopressin, a substance that helps regulate the biological clock. Theoretically, it might be possible to take eyedrops that control these cells, boost or suppress vasopressin levels, and so adjust the body's circadian rhythms manually. It's an idea that seems out of science fiction, and it's a long way from being put into practice, but the role of the eye in the body clock is a new area of science and we're still discovering how it might be useful — especially when it comes to jet lag.
Science is also identifying other areas in which jet lag may one day be beaten. Fiddling with the body's "master clock," which is in the brain's hypothalamus and seems to have a very big role in circadian rhythms, is one possible venue. The BBC reported in 2014 that scientists looking at the hypothalamus had discovered a protein in the brain that stops it adjusting too fast to new time zones; if the protein is removed in mice, they adapt to new circadian rhythms far faster. Other methods are a bit less high-tech; a study in 2016 of aircraft staff, who experience jet lag as part of their jobs, found that regulating meal times on their days off was hugely helpful for staff to adjust. Mostly, however, scientists tend to recommend good sleep hygiene once you've arrived as a key way to help get over the adjustment of your bewildered body, including avoiding stimulants like coffee and not going near screens before bedtime.
As somebody who is currently suffering from the woeful consequences of a 19-hour flight to Australia from the UK, these tips are helpful, but not a silver bullet. It's unlikely that a "cure" for jet lag is realistic; it may not be possible to make our bodies immediately adjust to a radically different time zone. But making the process a little swifter and easier would certainly be great for people like me, who spend their first few days in a new place bumping into walls.