Jet Lag. It's Just a Matter of Time

Dipesh Chaudhury, an assistant professor of biology at NYU Abu Dhabi, is entrenched in his office preparing for the classes he’s teaching this semester and working on his upcoming research. But his body and mind are ready to sleep. Having just returned from New York a few days earlier, Dipesh is jet lagged. The typical onslaught of daytime drowsiness was at hand, followed by “second winds” and caffeinated pushes to keep him active and prepared for his heavy load of classes and eye-opening research. But for him, the physiological effects take on a scientific meaning, as jet lag and the neurological processes behind the phenomenon are at the crux of his scholarship.

He shrugs it off, focused on the task at hand and says, with the conviction of a scientist, that it will “just” take five days to overcome. He says this knowing that, on average, that’s exactly what will happen as the neurological processes that define sleep re-entrain to the new time zone he is now in – a process the brain developed through millennia of evolution.

“This makes sense, biologically, evolutionarily, you’re not always just reacting to the environment, you’re getting ready to go hunting, to eat, to sleep. So, in a modern context, let’s say you go on a 12-hour trip, now you’re somewhere else, it’s 3 or 4pm and your body temperature dips because it thinks it’s 3 or 4am. This is all part of a system that then resets,” says Chaudhury, who also heads up a lab conducting multidisciplinary research to understand the link between stress and sleep.

Since the dawn of human existence, travel was a slow, natural movement. Be it at the speed of a horse or even boat, the body was able to adjust to the sun rising and setting at a slightly different time than the point of departure. But then almost a century ago, the marvel of flight allowed humans to travel at previously unknown speeds, spurring industry and cultural exchange, but also subjecting the human brain to the stress of a suddenly longer day or a seemingly endless night.

It’s precisely these changes in sunrise and sunset that disrupt the circadian rhythm or a roughly 24-hour cycle in the physiological processes of all living beings. Unsurprisingly, it’s triggered by light stimuli. So although our wrist watches may be set at the new time zone, the brain’s so-called master clock is stuck on the cycle of day and night from whence you came.

The circadian rhythm works with another neurological process known as the homeostatic sleep drive. The circadian clock prepares the body for being awake and going to sleep according to light stimuli, whereas the homeostatic process, or the part of the brain that promotes wakefulness and those that promote sleep, adheres more to a balancing act. Certain chemicals build up while being awake and eventually trigger the feeling of sleepiness. Adenosine, believed to be a chemical partly responsible for sleepiness, builds up while the parts of the brain for being awake are active. At a certain threshold, they create the desire to sleep, usually timed with circadian rhythm and making for a good night’s sleep – unless, of course, you’re jet lagged.

“You can stay up, you can game the system a bit. Caffeine, for example, is believed to block adenosine receptors so you can stay up longer. But often, you’ll notice that after traveling the first night you arrive, you sleep at a normal time. But it isn’t until the second or third night that jet lag begins taking hold, that’s when the clock takes over. The rhythm,” he said.

That rhythm, known as the brain’s master clock, is the punctual timekeeper of the body that keeps humans on a regular cycle of wakefulness and sleep. A normally functioning circadian rhythm will prompt your body with physiological processes responsible for each. For example, it’s the rhythm that will trigger your body to begin warming up moments before you naturally wake up and drop your body temperature when you’re expected to be in your deepest sleep at 3 or 4am. It will also send out melatonin into the system at mid-evening, when most of us are getting ready to sleep.

For humans, it runs effectively every day on slightly longer than the 24-hour cycle, reset through light sensitive receptors in our eyes that send messages to the brain indicating sunrise and sunset – our natural times of waking up and sleeping, respectively. Artificial light, from electronics disrupts this. But in drastic time zone travel, when suddenly the light receptors in our eyes begin receiving light signals consistently at times other than the usual, that reset button is triggered prematurely, or later in the day, and throws the system off-kilter triggering the symptoms of jet lag.

So now, the natural process of revving up the engines for waking up turn into hot flashes in the middle of the day, chills happen at dinner, and sleepiness hits at breakfast. Otherwise, the full-fledged symptoms of jet lag.

“What happens biologically, our brain receives the light information and it slowly resets to the new light cycle. And typically, what happens is it takes 5 days to re-entrain, so there is some truth to the idea that it takes a day for each hour of time difference involved in your jet lag. It’s just a matter of time,” he says.