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What Causes Jet Lag and How to Beat It

The science of jet lag and 11 tips to overcome it

Posted on January 21 2020

What is Jet Lag?

If you’ve crossed even a couple of time zones in one trip, then you know the feeling of jet lag. And the more time zones you cross, the worse the jet lag gets.

It’s difficult to fall asleep at night, or alternatively, you wake up in the middle of the night, unable to fall back asleep. In the daytime, you feel fatigued and want to nap at odd times of the day. It’s difficult to concentrate. You may have stomach problems like constipation or diarrhea, and you just generally feel unwell.

What is going on here?

Jet lag is the inability of your body to immediately adapt to sudden changes in your circadian rhythm. Circadian rhythms are biological changes (physical, mental, and behavioral) that follow a 24-hour cycle, cued by your own cells responding to lightness and darkness, eating and digestion, and exercise, among other things. These cues are known as zeitgebers (timegivers). A good example of one of these biological habits is when your body releases the hormone melatonin at the end of the day, which is its own chemical signal for sleep.

Our bodies prefer routine so that they can better anticipate and prepare for the day’s activities. These activities become the milestones of our day, together creating a physiological rhythm that is perhaps more important than we once realized. When you are taken out of one rhythm, and then given new light cues, eating cues, and activity cues all at different parts of the day, it can take a while for your confused body to catch up.

What Causes Leg lag?

Why can’t our bodies instantly adjust to a new time zone?

Researchers now believe that our genes our responsible: by looking at how mice brains responded to changed light stimuli (basically, forced jet lag), the genes SIK1 and CK1ε were found to be two culprits for jet lag. All mammals have the same core 24-hour circadian mechanisms, so examination of mice genes can point the way to our own circadian responses.

Light, received through photoreceptors on our retinas, is the main signal for our bodies to determine what time of day it is. This signal goes to the “master clock” called the suprachiasmatic nucleus, or SCN, that controls our circadian rhythms. The SCN contains about 20,000 nerve cells and is located in the hypothalamus, an area of the brain just above the optic nerves.

Researchers looked at the cellular DNA of the SCN to determine what genes were stimulated by light and found that, actually, a large number of genes were activated. These activated genes, in turn, start up the the 24-hour “autoregulatory feedback-loop,” telling our bodies when it’s time to eat, digest, get active, and eventually, go to sleep again. The SCN signals night at daytime through, among other things, variations in core body temperature and the secretion of hormones like cortisol and melatonin.

So, if all it takes is light, why can’t we adjust to a different time zone once we see the morning break in a new time zone?

Oxford researchers believe that while light switches on genes in our SCN, the protein called salt-inducable kinase 1 (SIK1) goes around and shuts those genes off again, essentially acting as a buffer to suppress the effects of light on the circadian clock. Researchers at the University of Manchester have found something similar for the casein kinase 1ε (CK1ε) gene. In the Oxford study, the research team found that by reducing SIK1 activity in mice, the mice were able to adjust to time zones in mere hours rather than six days! Similarly, with the inhibition of the CK1ε, mice recovered from their experimental jet lag ~2 days faster than regular mice.

Why do these genetic light buffers exist?

We probably evolutionarily developed them to prohibit any unreliable signals (a full moon, a bright bonfire) from affecting our sleep schedule. Oxford researcher Stuart Peirson noted: “If you think about it, it makes sense to have a buffering mechanism in place to provide some stability to the clock. The clock needs to be sure that it is getting a reliable signal, and if the signal occurs at the same time over several days it probably has biological relevance.”

With the invention of the light bulb and every subsequent glowing electronic (televisions, phones, tablets, computers…), our genetic light buffering system is actually a good thing… except for when we’re switching time zones.

As we better understand our circadian rhythms and our physiological responses to light, we can begin to develop better approaches to alleviating jet lag.

Interestingly, a drug that interferes with SIK1 and CK1ε light mechanisms has already been developed, but it is not yet ready for use with jet lag. Though we are on our way, our jet lag miracle drug has yet to be invented. Still, there are things we can do to get over the jet lag faster.

Tips for minimizing jet lag

1. Keep well hydrated

While keeping well hydrated won’t help switch your body clock any faster, mild dehydration is very common during travel and will make your jet lag symptoms feel even worse. So, step one is to drink plenty of water, and for optimal results, avoid alcoholic beverages because they contribute to dehydration (and can further disrupt your already disrupted sleep cycles).

2. Shift your clock before you travel

If you are planning to stay more than a day or two in a new time zone, it is a good idea to get a head start on your circadian shift BEFORE you travel. Look at the time of your destination, and spend the days before your trip slowly shifting your waking, eating, exercise, and sleeping schedule to match that time zone. Depending on which direction your flying, this may mean getting up earlier (going east) or staying up later (going west). Even shifting your circadian rhythm an hour or two before a major time-zone change can help a lot!

3. …Unless you’re only staying for a day or two

If you are only travelling to a new time zone for a day or two, it may not be worth it to try to adjust your body. In that instance, try to stay on a sleeping and eating schedule closer to your own time zone while you are abroad. Keeping your phone clock or watch set to your home time zone may help you remember when to eat and sleep.

4. Adjust to your new time zone as quickly as possible

Though it may be difficult, try to set a consistent time to wake up every morning, and each night stay up until local bedtime. In the morning, try to get as much natural light as possible to signal your SCN and your circadian clock that it’s time to start the day! (More on this in tip #8) Keep active during the day, but not so active that you’ll exhaust yourself and want to go to bed too early. You may want to nap, but remember:

5. Keep naps short and well away from bedtime

Long naps or naps too close to bedtime will disturb your sleep and probably prolong your jet lag. Instead, take a short power nap (30 minutes or less) in the late morning or early afternoon to restore energy but avoid unwanted sleep inertia or grogginess.

Quick plug: our nap feature in Pzizz is perfect to assist you with your power naps, getting you to sleep quickly and helping you wake up feeling refreshed!

6. To sleep on the plane, or not to sleep on the plane?

Before you settle in for a long plane snooze or full-on first class reclining seat bedtime, consider what the time it is in your destination. If it’s daytime at your destination, then you’ll arrive rested and ready to start the day… at 10 PM?! If that’s the case, it may be better to forego sleep on the plane and, instead, work, read or watch films on the plane. On the other hand, if you’ll be arriving in the early morning, then try to get to get some good shut-eye during your flight and start your day in your new destination.

7. Get comfortable

If you’ve determined that you should get some sleep on the plane, it may be MUCH easier said than done. Give yourself the best chance by maximizing your comfort. If you can, splurge on seats with more room or that can fold down completely. Consider a good neck pillow, cozy socks (try compression socks for better circulation), loose or flexible clothing, blankets, noise-cancelling headphones or earplugs, soft eye-masks, contact lens case for your contacts, and even toothpaste and a toothbrush for long flights.

8. Light and dark

The power of light!

Light exposure is the most important, impactful environmental cue our bodies have for setting and maintaining our circadian synchrony. As such, we can either use light or avoid light to help us reset our circadian rhythms more quickly in a new time zone. Photoreceptors in our retinas called ganglion cells, which are neither rods nor cones, do not convey visual information but do convey light information to our brain’s masterclock. These non-visual photoreceptors contain the photopigment melanopsin, which is especially sensitive to wavelengths in the blue-green spectrum. This suggests that exposure to light that is highly concentrated with wavelengths in the blue-green spectrum would be the most effective at shifting our circadian rhythm and helping us beat jet-lag more quickly.

Researchers have determined that the two most important factors for light exposure causing a phase-shift in your circadian rhythm are the 1) intensity of light, and 2) the timing of the exposure. The intensity of light is literally the amount of light that your eyes are exposed to, whether it’s a bright room emitting 500–1,000 lux of light or a cloudless, midday, sunny sky emitting 110,000–120,000 lux. The timing of the exposure will dictate how the circadian shift will occur.

For example, if you expose your eyes to bright blue light at 10 PM, your body will stop producing as much melatonin, and you will want to stay up later. If you expose your eyes to bright light at 4AM, earlier than the sun rises, you’ll suppress nighttime melatonin and begin to wake up earlier in the morning.

One study demonstrated that the intensity of light does directly correlate to the amount of melatonin suppression. Low illuminances caused little change in plasma melatonin concentrations, while bright room light and high illuminances completely suppressed the production of plasma melatonin. In this study, researchers showed that the body’s response to light occurs in a stepwise manner:

  • Below 80 lux of light, very little melatonin suppression occurs.
  • Between 80–200 lux, some people exhibited more melatonin suppression, while others did not.
  • Over 200 lux, suppression of melatonin does occur.
  • Over 500 lux (a bright room), a saturating amount of light causes a phase-shift, and melatonin is greatly suppressed.

In summary, exposure to 200 lux of light can suppress melatonin, and exposure to over 500 lux of light will begin to cause a phase shift, forcing our bodies to try to adapt to a new sleep cycle. To avoid any melatonin suppression, keep light levels below 50 lux.

So, how can we apply all of this great research to our lives so we can keep jet-lag at bay?

Here’s what to do: if you’re feeling tired during the day or early evening before you want to go to bed, make sure you are getting exposure to plenty of light. The best thing is to be outside in the sunlight or inside in a brightly lit room. If it’s very cloudy or dark outside, or you have to be inside in low lighting, there are a number of tools available to you.

The easiest tool is probably already in your pocket: your cell phone can emit around 350–400 lux if you hold it about two feet from your face. Turn the brightness up and the night shift off (in this case, we WANT all of that blue light!), and check your e-mail for a while.

You can also buy small, portable LED lights with 1,000 lux output like this one to help you phase-shift your clock. LED lights have a higher concentration of blue light than incandescent lights, making them perfect for melatonin suppression.

Other companies have bona fide jet-lag fighting gadgets to help you get the right amount of light.

Retimer offers green-and-blue-light-emitting futuristic glasses, meant to be worn for 60 minutes a day in the morning or evening (depending which direction you’d like to phase shift).

The Human Charger actually emits ~350–400 lux of light into your ear, where additional photoreceptors are found. Because you simply wear The Human Charger like music earbuds, it is very convenient to wear around!


While bright light suppresses the production melatonin, darkness cues our body to begin secreting it.

If you wake up too early in the morning from jet-lag, continue to keep your bedroom dark to help your body understand it is still nighttime.

If you get out of bed, keep the lights dim as you begin your day. If you must look at your phone or computer, make sure the night shift mode is on, so the blue-green light spectrum is reduced. The same is true if you are having trouble getting to sleep at night.

To encourage melatonin production, keep your surroundings dark, wear a sleeping mask, or at least keep light sources at low intensity (especially blue-green light-emitting devices).

8. Artificial melatonin

As we’ve previously discussed, nighttime darkness initiates the release of melatonin, the hormone that the body produces to signal to itself that it’s time for sleep.

The body naturally produces melatonin in the pineal gland, but it can also be synthesized artificially. It is sold over-the-counter as a popular nighttime sleep aid. Multiple studies have shown the efficacy of melatonin supplementation to treat jet-lag.

For example, one 1993 study showed that melatonin (5mg) was most effective when taken at night after flight attendants had landed in their new time zone; it was not statistically advantageous for the flight attendants to begin their melatonin regime in the days leading up to their departure.

Another study determined that the most effective dosage to treat jet lag is between 0.5 and 5 mg of fast-release melatonin taken at bedtime for four days. While the 0.5 mg and 5 mg doses performed similarly in terms of overall efficacy, the 5 mg dose did allow patients to fall asleep faster and get better sleep. Slow-release melatonin was found to be much less effective than the fast-release melatonin.

Artificial melatonin has been found to be most effective when travelling eastward five or more timezones (when you’ll have an earlier bedtime than you’re used to), or when travelling westward with a change of 12 time zones or more. Most reports indicate that 3 to 5 mg of fast-release melatonin taken 2 to 3 hours before bedtime for up to four days will be the most effective method for treating jet lag.

So, during your next long-distance timezone-changing flight, follow these guidelines and try artificial melatonin before bedtime to improve your jet-lag symptoms!

Also note: Studies have shown that despite the fact that melatonin is produced naturally in the body, it is not necessarily “safer” than other prescription sleep aids when used in the long term. Although the proper dosage of melatonin to treat chronic insomnia is thought to be 0.3 milligrams, many supplements sell dosages at ten times that amount. Not only can melatonin overdose lead to hypothermia and continually high melatonin levels (causing a lethargic, hangover-like effect), but also, after a few days of those high dosages, the brain’s melatonin receptors become inundated and the supplement no longer works.

9. Fasting

In the early 1980s, senior research scientist Dr. Charles F. Ehret at the Argonne National Laboratory in Illinois determined that jet lag symptoms can be diminished or even eliminated with intermittent fasting and dieting during the days leading up to a long, time-zone changing trip.

Based on earlier results from metabolic studies to prevent artificial jet lag in mice, Ehret developed the Argonne anti-jet lag diet, which alternates days of “feasting,” eating high protein breakfasts and high carbohydrate dinners, with days of “fasting,” eating only small, low-calorie meals of salads, thin soups, and fruits.

The diet also includes instructions on the appropriate days and times to consume caffeinated and alcoholic beverages. On the day of travel, the traveler fasts until he or she can consume a high protein breakfast at his or her destination. Ehret believed that the diet worked because the days of irregular eating patterns shocked the body out of its normal biological rhythms, and the big breakfast and subsequent meals in the new destination reset the biological rhythms once again.

The Argonne diet (four days of alternating moderate feasting and fasting to prevent jet lag) was tested in 2002 on 186 National Guard personnel deployed across nine time zones. Results showed that jet lag was consistently less frequent for Argonne-dieters in both eastward and westward travelling directions.

In travelling from the United States to South Korea for deployment, Argonne-dieters were found to be 7.5 times less likely to experience jet lag than a control group. On the return trip from South Korea to the United States, Argonne-dieters were found to be 16.2 times less likely to experience jet lag than the control group.

If you are disciplined enough to endure two entire days of fasting (with a day of feasting between), then this Argonne anti-jet lag diet may be worth looking into.

More recently, researchers found a preventive jet-lag treatment with another, slightly easier approach to fasting.

Harvard Medical School Professor Dr. Clifford Saper and his colleagues at Beth Israel Deaconess Medical Center, Boston, discovered that a second neurological “master clock” called the dorsomedial nucleus is affected by changes in food and hunger. Their research suggests that fasting before flights may be able to re-synchronize body rhythms in jet lag much faster than light and dark therapy.

Saber suggests fasting for 12 to 16 hours before landing at your final destination, and then upon arrival, eating a large meal as close to a local mealtime as possible.

This approach is similar to the Argonne anti-jet lag diet, but cuts out the “feasting” and “fasting” days before the day of travel.

In theory, the Harvard anti-jet lag fast works because, when food is scarce, the brain discourages the body from sleeping normally. Fasting effectively suspends the circadian clock, which is then re-activated and re-calibrated upon eating. This other, food-controlled “master clock” most likely evolved because when our prehistoric ancestors were starving, they needed to be able to forage for food, despite their routined sleepiness.

Harvard researchers have yet to run human trials to scientifically determine the fast’s efficacy, but anecdotal evidence looks promising so far.

So, the next time you’re in for a long, timezone-altering flight, try the 12–16 hour anti-jet lag fast for yourself! Just don’t forget jet lag Rule #1: even if you’re fasting, stay HYDRATED.

10. Exercise

Although generally thought to be a weaker zeitgeber than light exposure or eating habits, exercise is another method to help reset your biological clock in a new time zone.

It is inherently difficult to separate daytime exercise with light exposure in scientific trials, and therefore there are no studies about how exercise alone affects jet lag.

One University of Toronto study on hamsters demonstrated that exercise did improve artificial jet lag, reducing the adjustment period from 5.4 days to 1.6 days or 11.6 days to 1.5 days, depending on the night time light levels. The hamster results suggest that, among people who are physically fit, appropriately scheduled exercise may well help fend off jet lag in human subjects as well.

Light exercise in bright sunlight is generally regarded as a good tool for resetting your biological clock, not only because the sunlight sends “it’s daytime” signals to your SCN, but also because muscles have their own circadian functionality where they perform more efficiently in waking hours than sleeping hours. In the first few days in your new time zone, light exercise, rather than grueling workouts, can boost energy levels and avoid causing potential daytime exhaustion. Once you have acclimated to your new timezone, more rigorous workouts can be resumed.

It should also be noted that regular, daily exercise (not just during trips) seems to lessen jet lag symptoms as well. A study at Amherst College demonstrated that aged mice that regularly, voluntarily exercised were less susceptible to the adverse effects of circadian rhythm disruption (like jet lag). This study implies that a lifestyle with regular exercise may generally reduce symptoms of jet lag in humans as well (surprise, surprise).

11. Pzizz!

While Pzizz has not yet completed studies demonstrating its efficacy for treating jet lag, anecdotal evidencehappy customers, and various articles suggest that Pzizz is one of the best apps to put you to sleep in your new time zone.

Pzizz’s app plays you a sleep-optimized mix of music, voiceover, and sound effects that change each night, that will quickly quiet your mind, put you to sleep, keep you asleep, and wake you up feeling refreshed.

We combine the science of psychoacoustics, clinical sleep interventions and personalization through learning algorithms. It’s wild and incredibly effective. So whether you’re trying to fall asleep in the plane or your hotel room, give it a try for your next trip!

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