Jets Leave Your Rhythms Behind
Jet lag is a young problem. Before jet planes, most long trips happened by ship or train, which were too slow to throw off the body. So the word only appeared once jets did.
Its first known use was in a Los Angeles Times article on 13 February 1966. Writer Horace Sutton gave a perfect summary: "jets travel so fast they leave your rhythms behind." The term caught on quickly and is still growing in use.
The feeling was noticed even earlier. A 1969 study by the Federal Aviation Administration found that the aviator Wiley Post was the first to write about the effects of flying across time zones. He did it in his 1931 co-authored book, Around the World in Eight Days. In the 1970s, scientists finally linked jet lag to the body's daily rhythms rather than plain tiredness from travel.
The Tiny Clock in Your Brain
Your body runs on a circadian rhythm, an internal daily cycle that sets times for sleep, eating, hormones and body temperature. Its master clock is the suprachiasmatic nucleus, a small area in the brain's hypothalamus. Here is a surprise: in humans this clock runs slightly longer than 24 hours, so it needs resetting every day.
The strongest reset button is light. Scientists call cues like this a zeitgeber. Light signals reach the master clock through the eyes, and meals and daily activity help too.
The twist is that your organs have their own clocks. Your muscles, liver and lungs may adjust at different speeds, lagging behind the brain. So after a long flight, your body is out of step with the local time and also out of step with itself. Researchers call this double desynchronisation, and it may explain why jet lag can feel so strange and messy.
Why Direction Beats Distance
Jet lag depends only on how far you travel east or west. A ten-hour flight between Europe and southern Africa causes no jet lag, because you are heading mostly north to south. You may still feel worn out, but that is travel fatigue from dry air, cramped seats and little movement. A four-hour flight from Miami to Phoenix, on the other hand, can cause real jet lag.
Most travellers find flying east harder. Fly from New York to London and your body feels as if it is five hours earlier than the local time. Crossing the International Date Line does not add anything, because only the number of time zones counts, up to 12 hours either way.
On average, it takes about one day per hour of time difference to fully adjust. Night owls tend to handle westward trips more easily. People over 60 are more sensitive to these shifts, and some people even notice a single hour of daylight saving time.
Tricks to Reset Your Clock
Light is the main tool. Morning light shifts your clock earlier, which helps when flying east. Evening light shifts it later, which helps when flying west. Timing is everything, so the US Centers for Disease Control and Prevention recommends apps that tell you when to seek light, avoid it, drink caffeine and sleep.
Melatonin, a hormone your body releases at night, works almost as the opposite of light. Taken in the afternoon or early evening, it moves your clock earlier. Taken in the morning, it moves it later. Using both light and melatonin together can speed things up. But athletes need care, because anti-doping agencies may limit melatonin.
You can also start early. Shifting your sleep by 1 to 2 hours before leaving can shorten jet lag. For very short trips, just staying on home time may work. And many athletes arrive at events like the Olympics 2 to 4 weeks early to adjust.
Moonlit Upsides and a Pill From Japan
Jet lag even has a fan or two. British businessman Alistair McAlpine, a frequent traveller to Australia, wrote in a 2002 memoir that being wide awake at odd hours let him see the last hours of a full moon over Sydney Harbour. He also loved the fresh feel of dawn walks in the Botanical Gardens.
Science is chasing better fixes. Cordycepin, a substance based on a natural fungal compound, helped mice adjust faster after a sudden shift in their light and dark cycle. It works on a protein that affects genes tied to the body clock.
The most exciting news came in February 2026. Japanese scientists found an oral compound called Mic-628 that resets the body clock by targeting a gene called Per1. It cut jet lag recovery time in half. Even better, a single dose moved the clock earlier no matter what time it was taken.
