It's four in the morning and you're stuck in your hotel room, bored out of your skull but wide awake. Thanks jet lag! That's the price you pay for changing so many time zones in a single plane ride. Here's why it happens, and how you can prevent it from ruining your trip.
Jet lag is, simply, a breakdown in your circadian rhythm caused by rapid travel through multiple time zones. Say, for example, you were to fly from San Francisco to New York City. Your body doesn't have time to adjust to the three-time-zone difference over the course of the flight, so your body "thinks" that it's three hours earlier than what your watch says. And until your internal clocks can reset themselves to the local time, you're left groggy and tired.
The severity of jet lag depends both on the traveller and the trip. North to south trips and shorter (1-2 time zones) east to west trips do not cause as noticeable lag as cross-country flights. Additionally, some people's circadian rhythms take longer than others to reset. In all, however, the maximum amount of jet lag one could potentially endure is plus or minus 12 hours. Interestingly, adjusting to losing hours (travelling west to east) is significantly harder than adjusting to gaining them (travelling east to west). The former requires roughly 2/3 of a day per time zone crossed to recover from, while the latter demands just half a day.
So circadian rhythms are the main culprit. What are they exactly, and can you beat find a way to beat them?
Circadian rhythms have been widely observed in the natural world and throughout history, and all living things are subject to their demands. The process was first recorded in the 4th century BC by Roman sailors, and has made multiple appearances in both Eastern and Western medical texts since then. By the turn of the 20th century, medical researchers had roughly deduced the length of the rhythm to be roughly 24 hours, but it wasn't until the mid 1970s that medical science first discovered the its genetic components, and not until 1994 that we uncovered the mammalian '"clock gene." A recent Harvard study pinned the rhythm for an average healthy adult to precisely 24 hours and 11 minutes, give or take 16 minutes.
While we are just beginning to understand the process, circadian rhythms are one of nature's oldest inventions. Evolutionary biologists believe it may have begun as a way for early cells to protect their DNA from damaging ultraviolet radiation during daylight hours (remember, this was before the planet grew a proper ozone layer). By developing photosensitive proteins and a circadian rhythm, these primitive lifeforms would have only attempted DNA transcription in the relative safety of nigh.
But it's not just cellular division that's governed by these internal clocks; a number of processes including regulation of the sleep cycle, metabolism, body temperature, thirst, appetite, and hormone levels are all synchronised across the body's various organs by this photosensitive system. Which is why jetlag causes more problems than just making you tired.
To keep all of these varying processes locked in step, the human brain is also equipped with a "master clock" by which all of the body's other clocks are set. Known as the suprachiasmatic nucleus (SCN), this relatively small structure is tucked away in the brain's hypothalamus region and consists of just 20,000 nerve cells.
The SCN is charged with interpreting light-level information garnered by specialized photosensitive ganglion cells located in the retina, and passing that information on to the pineal gland, which regulates your sleep cycle by controlling the amount of melatonin it produces. So basically, when your eyes signal to the SCN that it's getting dark out, the SCN will mandate an increase in melatonin, which makes us sleepy.
In other words, it's not just the sleep you're missing out on or that travelling makes you tired. When you cross time zones, your body is actively working to tire you out.
Currently, the best method for getting through jet lag is to simply tough it out. Caffeine and sleep aids can help, as can exercise and seeking light exposure at certain hours of the day. People travelling east by more than four time zones should avoid bright lights in the morning hours and actively seek them out in the afternoon to help reset the circadian rhythm.
Setting your watch to the destination time zone and working on that schedule, even just for the duration of the flight, can also help minimise the chronological shock. And, if you're really desperate, melatonin is sold over the counter as a health supplement. Just be sure to follow the label directions exactly (taking too much is counter-productive).
We might not be far, though, from instant adaptation to our new surroundings. A team of researchers from Oxford University has discovered what they're calling the "jet lag molecule". While studying the SCN region in mice, the team noted that a single protein called SIK1 consistently deactivated photosensitive cells, effectively acting as a molecular brake to prevent them from rapidly adapting to lighting changes. In other words, slowing down the jet lag effect.
Inhibiting the SIK1 protein had immediate and appreciable effects. Prof Russell Foster told the BBC:
We reduced levels by 50-60%, which is big enough to get a very, very big effect. What we saw was the mice would actually advance their clock six hours within a day [rather than taking six days for untreated mice]. We've know there's been a brake on the clock for some time, but we had absolutely no idea what it is, this provides a molecular basis for jet lag and as a result new targets for potentially developing new drugs.
It will still be some years before we can simply pop a pill and reset our body clocks, but ability to do so could prove useful in fields far beyond commercial air travel. Astronauts, especially, will need a means of adapting their circadian rhythms to slightly longer Martian days, while Earth-bound shift workers will be able work longer and recover faster. It could even be used as a treatment for schizophrenia and bipolar disorder, both of which are associated with malfunctioning circadian rhythms.
Until then though, your best cure is the same it's been for decades: coffee, complaining, and giving your body a little bit of time to reset its clock.