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What is Jet Lag? Symptoms, Causes, and Treatments

Jet lag happens when you fly across time zones and your internal body clocks take time to catch up. Here’s what exactly causes it and what to do about it.
Published
2022-07-11
Updated
17 MINS

If you’ve ever struggled to fall asleep after flying to a new destination, despite it being past midnight, or woken up for the day, but it’s 3 a.m. outside, you’ve experienced jet lag. Though you’ve physically flown across time zones, your body clock is still back home and can take days to catch up, leaving you feeling groggy, irritable, and mentally and physically not at your best. 

It’s thought one-third of travelers don’t experience jet lag at all, but for those of us who do, the symptoms can ruin the start of our vacations and leave us feeling off for days when we’re back at work after a trip. It may even put us off international travel altogether. But it’s not just a problem facing tourists. Everyone from politicians to military personnel, competitive athletes to business travelers can experience jet lag and its effects.

While you can’t avoid the symptoms of jet lag altogether, there are things you can do to speed up the adjustment process.

In this blog post, we’ll give you an overview of what jet lag is, what causes it, and a few of the key techniques you can use to recover faster on your next trip. 

What is Jet Lag?

The American Academy of Sleep Medicine says “jet lag disorder (JLD) is a temporary circadian rhythm disorder related to travel across time zones in which there is a misalignment between the timing of the sleep and wake cycles generated by the endogenous circadian clock and that required in the new time zone.”

What exactly does that mean? Let’s look at jet lag in simpler terms.

Jet lag happens when you travel across different time zones fast. The more time zones you fly over, the worse your symptoms are, and you’ll almost always feel jet lag when flying over three time zones or more. Your body clock, also known as your circadian rhythm, is no longer in sync with the outside world and you’re left feeling tired and awake at odd times, and simply not feeling or functioning your best. 

For example, if you get a plane from New York to London, you’re suddenly jumping forward five hours, but your body can’t adapt in the time it takes to fly there, so it’s still running on New York time.

Londoners may be winding down for bed at 11 p.m. but your body thinks it’s only 6 p.m., so it’s nowhere near ready to sleep. And then come morning, you struggle to pull yourself out of bed at 8 a.m. because it’s actually 3 a.m. in your body. 

On the other hand, when you’re back home in New York, you start feeling sleepy at 6 p.m., as it’s actually 11 p.m. for your unadjusted body clocks. But then you may wake up at 3 a.m. and find it impossible to fall back to sleep as it’s now 8 a.m. in London and in your body.

While some researchers say jet lag is only caused from flying east or west, one study found you can actually experience it even if you’re flying north or south. That’s because even though you may not be changing many, or any, time zones, the change in daylight duration can still throw off your body clocks. 

What Are the Symptoms of Jet Lag?

Everyone experiences jet lag differently, and the severity of your symptoms will depend on how far you’ve traveled, your age (older adults feel the effects more), and your chronotype (whether you’re a morning or night person).

The main symptoms of jet lag are: 

  • Sleep problems — including struggling to fall asleep at night, waking up too early and struggling to get back to sleep, and waking up often during the night 
  • Daytime sleepiness 
  • Lowered alertness 
  • Loss of concentration
  • Appetite loss and feeling hungry at odd times 
  • Digestive issues  
  • Low mood and irritability 
  • Poor performance — mentally and physically 

You can learn more about jet lag symptoms here to discover the short and long-term symptoms as well as what exactly is causing them.

What Causes Jet Lag?

Jet lag is caused by two things: 

  • Misaligned circadian rhythms — in other words, your body’s internal clocks don’t match the outside world 
  • Sleep deprivation from traveling

Circadian Misalignment 

As jet lag is a circadian rhythm sleep disorder, it‘s helpful to understand what exactly this rhythm is. 

Your circadian rhythm is your internal body clock that runs on a roughly 24-hour cycle. It’s controlled by a central pacemaker called the suprachiasmatic nucleus (SCN), which is in the hypothalamus region of your brain. This is known as the master clock and it controls your sleep-wake cycle, as well as things like your body temperature and hormone production. It also sends messages to the other clocks in your body. That’s right, there’s more than one. 

In fact, nearly every tissue and organ system in your body is running on a circadian clock. These kinds of clocks are called peripheral clocks and you’ll find them in your immune system, metabolism, and digestive system, for example. 

The timings of our circadian rhythms can change, but they’ve evolved to adapt slowly over the year as the seasons change for example, not rapidly with air travel. So, when you fly across time zones, your inner circadian rhythms are suddenly at odds with the local time — and this is the main reason for jet lag. 

To make things more complicated, your master clock and peripheral clocks adapt to time zone changes at different rates. While it’s hard to know in humans, research with rodents suggests organs like the liver and lungs and muscles can take nearly six times as long as the SCN to adjust to jet lag. 

Sleep Debt

The RISE app works out how much sleep debt you have.

Beyond misaligned circadian rhythms, long flights often cause a lot of sleep deprivation, and this can also contribute to jet lag. 

When you miss out on sleep, you rack up something called sleep debt. ​​Sleep debt is the amount of sleep you owe your body over the last 14 nights. It’s measured against your sleep need, the unique genetically determined amount of sleep you need.

While many of us live with sleep debt back home, it’s all too easy to rack up large amounts of sleep debt when traveling. Maybe you had a 2 a.m. flight then only got a few hours shut-eye while on board.

With high sleep debt, you’ll feel tired, groggy, and irritable. And the situation is only made worse if you have trouble sleeping after you arrive at your new destination, which you likely will if you’re now out of sync with your circadian rhythm. 

To find out if you’ve got high sleep debt, you can turn to the RISE app

How Long Does Jet Lag Last?

You’ll experience jet lag symptoms all the time your circadian rhythms are trying to adapt to your new time zone, so the symptoms are usually short term and they‘ll go away on their own. How long you feel jet lag for depends on the number of time zones you‘ve crossed. 

For most people, it takes almost a day for every time zone you cross to adjust. So, for that New York to London flight we talked about earlier, it may take you five days to recover, as you’re crossing five time zones. 

However, things like your chronotype and age can affect how long it takes you to recover. Plus, your peripheral clocks may take much longer to catch up, so you may feel certain symptoms for longer than others. (Remember, research shows peripheral organs may take six times as long as the SCN to adjust). 

What’s more, it takes longer to adjust after traveling east than it does west. That’s because the average circadian rhythm is actually slightly longer than 24 hours (under experimental conditions, it’s 24.2 hours to be exact), so we’re naturally inclined to stay up later and delay our clocks more than advance them. 

Even more bad news? When your circadian rhythms are caught up to the external world, you may still feel the effects of high sleep debt if you haven’t paid this back, meaning you could still feel groggy and just not your best.  

We cover how long jet lag lasts in more detail here. And keep reading to find out the good news (that you can speed up the recovery process). 

How Can You Recover from Jet Lag?

You may not be able to avoid jet lag all together, but there are some things you can do before, during, and after your flight to speed up your adjustment to your new schedule. 

We dive deeper into how to get over jet lag here, but here are a few interventions to get you started. 

Be Strategic About Light 

Light exposure is the most powerful zeitgeber, which is German for “time-giver” and means an external cue that can reset your circadian rhythm. Your SCN responds directly to the light-dark cycle, so being strategic about light exposure can help it adjust faster. 

Timing your light exposure is also one of the easiest things you can do to help you get over jet lag as you don’t need any special equipment or to take any medication. In fact, one study says: “One of the simplest jet lag strategies is to promote and restrict exposure to natural sunlight at specific times.” 

You just need to get the timing of your light exposure right depending on your direction of travel. 

The study recommends, if you’re flying west, getting light exposure in the early evening and first half of the night according to your old time zone. You should avoid light in the second half of the night and earling morning. And if you’re flying east, do the opposite. 

However, the study does note it’s hard to follow these recommendations as you’re traveling through brightly lit airports and planes. This means more studies need to be done to determine the exact timing of light exposure. 

For example, award-winning science journalist Linda Geddes recommends a slightly different approach in her book Chasing the Sun

When flying east: 

  • Get light exposure between 6 a.m. and 6 p.m. (especially at 9 a.m.) in the time zone you’re leaving. This will advance your body clock, bringing the timing of your bedtime and wake time earlier.
  • Avoid light outside of these times (especially at 3 a.m.) by wearing sunglasses or sleeping if it’s nighttime in your new time zone. 

When flying west:   

  • Get light exposure between 6 p.m. and 6 a.m. (especially at 3 a.m.) in the time zone you’re leaving. This will delay your body clock, pushing the timing of your bedtime and wake time back.
  • Avoid light outside of these times (especially at 9 a.m.) by wearing sunglasses or sleeping if it’s nighttime in your new time zone.

Natural light is best for making these shifts, but you can turn to a light box if that’s not possible. 

Take Melatonin Supplements 

Melatonin supplements are an artificial version of the natural hormone your brain makes to get your body ready for sleep. By taking a supplement, you can trick your body into thinking it’s time to wind down for bed. You can learn more about what melatonin does here. 

There are several studies showing how melatonin can be used to shift your circadian rhythm forward or backward, but, just like with light, you need to get the timing right. 

More research still needs to be done to find the ideal dose and timings, but here’s what one study recommends after analyzing several trials:  

For eastbound flights up to 9 hours long: 

  • Prepare before the flight: Take 5 mg of melatonin, wake up earlier, and get bright light exposure.
  • Day of the flight: take 5 mg of melatonin at 6 p.m.
  • After the flight: take 5 mg at bedtime until adapted, and get 30 minutes of outdoor exercise to help speed up the process. 

For westbound flights up to 9 hours long: 

  • Prepare before the flight: Take 1 mg of melatonin after waking up and gradually start waking up later. 
  • Day of the flight: 1 mg after waking up 
  • After the flight: Stay up until your new target bedtime and get natural light exposure. Take 1 mg after waking up. 

For flights in either direction that are 10 to 14 hours long: 

  • Prepare before the flight: Stay up later and get light exposure. Take 1 mg after waking up.
  • Day of the flight: 1 mg after waking up.
  • After the flight: 30 mins of outdoor exercise in the morning and afternoon. Take 5 mg at bedtime.

Heads up: While it may be tempting to reach for an over-the-counter sleep aid to help you fall asleep, they come with side effects, long-term health risks, and they don’t work to change the timing of your circadian rhythm.

Reduce Sleep Debt and Sync Up with Your Circadian Rhythm Before Flying

The RISE app predicts your circadian rhythm each day.

You can also make sure you’re going into jet lag with the best foundation. By making an effort to pay down your sleep debt and get in ideal circadian alignment before your flight, you can make sure your jet lag symptoms are as reduced as they can be.

If you’re going to start adjusting to your new time zone a few days before your trip, however, you should aim to be in sync with your circadian rhythm up until this point. 

Keep an eye on your sleep debt with RISE in the lead up to your trip. We recommend keeping it below five hours to feel and perform your best. 

 If you’ve got high sleep debt, you can pay it back by: 

  • Taking naps: Check RISE for the best time to do this so you don’t disturb your sleep that night. 
  • Going to bed a little earlier
  • Sleeping in a little later: Keep this to an hour or two so you don’t disrupt your circadian rhythm. 
  • Maintain excellent sleep hygiene: This is the set of behaviors you can do throughout the day to help you fall asleep faster and wake up less often during the night, therefore getting more sleep overall. 

You should also keep an eye on your sleep debt after you’ve arrived in your new location. Wherever possible, keep it low to avoid symptoms of sleep deprivation as well as jet lag. 

Beyond sleep debt, consider your circadian rhythm. You can either make sure you’re as aligned with your circadian rhythm as you can be before setting off or aligned before you begin adjusting to your new time zone, if you’re doing this a few days before your trip. 

The RISE app predicts your circadian rhythm each day based on things like how long you slept for last night and your inferred light exposure. You can then see when your body naturally wants to be awake and when it wants to head to bed. Stay as closely aligned to this in the lead up to your trip or adjustment period as you can. 

Bonus tip: Keeping your sleep debt low and staying in circadian alignment can help you feel your best each day, even when you’re not traveling.  

Why Do I Feel Like I Have Jet Lag Without Traveling?

If you’re feeling tired during the day, wired at night, and generally not performing your best, you may have jet lag. But what if you haven’t left your time zone? Then you may have a different kind of jet lag called social jet lag. Social jet lag happens when our internal body clocks are at odds with the outside world

How does this happen without long-distance travel? Social jetlag can be caused by: 

  • Irregular sleep patterns: Perhaps you stay up later at the weekends than you do during the week and indulge in a weekend lay in.  
  • Shift work: You’ll have social jet lag if your shifts are constantly changing, too. 
  • Not being aligned with your chronotype: If you’re a night owl living like a morning person, especially if you revert back to your night owl ways every so often, you’ll feel the effects of social jet lag. 

If you have social jet lag, you’re not alone: 87% of adults have social jetlag and go to bed at least two hours later on weekends. 

You can overcome social jetlag by: 

  • Keeping a consistent sleep schedule: As tempting as a Saturday lay in feels, try to wake up at the same time each day, even on weekends. 
  • Getting natural light in the early morning: Get at least 10 minutes of sunlight as soon as possible after waking up to reset your circadian rhythm for the day. This will help you feel sleepy come bedtime to help with that consistent sleep schedule. 
  • Improving your sleep hygiene: RISE can guide you through 20+ sleep hygiene habits that will help you keep your sleep-wake times in sync with your circadian rhythm. These habits include avoiding caffeine too close to bedtime, putting on blue-light blocking glasses 90 minutes before bed to stop artificial light keeping you up, and wearing an eye mask and earplugs to bed to stop light and noise disrupting your sleep. 

Many of us, depending on where you live, experience a sudden shift in the clocks twice a year for daylight saving time, and this too can leave us feeling out of sorts as we adjust. You can learn how best to adjust to daylight saving time here.

You may also feel the symptoms of jetlag without traveling if you’ve got high sleep debt. Sleep deprivation messes with everything from your hunger hormones to your ability to focus to your mood. Plus, of course, you’re left feeling tired and groggy during the day. 

Follow our tips above (like taking well-timed naps) to help you pay back sleep debt, and keep track of it with RISE to keep it low in the future, so you can always feel your best. 

Speak to a healthcare professional if you’re constantly feeling jet lagged to rule out underlying conditions. 

Sleep Easy at Home and Away 

Jet lag happens when your internal circadian rhythms are out of sync with the outside world after long-haul travel. It may take a few days — depending on how far you’ve traveled — to catch up. And while there isn’t a cure, things like well-timed light exposure and melatonin supplements can help speed up your adjustment to the new time zone. 

The RISE app can help, whether you’re overcoming jet lag, battling social jet lag, or looking to optimize your energy levels at home. You can use the app to track your sleep debt, to keep it low, and predict your circadian rhythm, to stay in sync with it. Plus, RISE can remind you when to do 20+ sleep hygiene habits to help you meet your sleep need each night and feel your best each day. 

Learn more about how circadian alignment drives daily energy and how to support it:

Summary FAQs

How does jet lag feel?

The main symptoms of jet lag are daytime tiredness, trouble sleeping at night, trouble concentrating and staying alert, digestive issues, and impaired mood and performance. Learn more about jet lag symptoms here. 

What is jet lag in simple words?

Jet lag happens when you travel across time zones and your internal body clocks are no longer in sync with the outside world. If you fly from New York to London, it may be midnight in London, but your body is still on New York time, so it thinks it’s only 7 p.m. and you’ll have trouble falling asleep.

What is jet lag and why does it occur?

You’ll feel jet lag when you travel across time zones and your internal body clocks are no longer in sync with the local time. Your body clocks evolved to adjust slowly, not in one long haul flight, so you experience daytime tiredness, trouble sleeping, and subpar performance while you adjust. 

How do you cure jet lag?

You can’t necessarily cure jet lag, but you can reduce how long it takes to adjust. Be strategic with your light exposure, consider taking melatonin supplements, and keep sleep debt low to speed up recovery.

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