What Is Jet Lag?

Countless travelers experience the discomfort of time zone changes after air travel. It’s a common phenomenon known as jet lag, and it’s one of the least enjoyable things about traveling.

Jet lag is an unpleasant, temporary sleep disorder associated with long-distance east-west travel. The body’s circadian rhythm often experiences difficulty adjusting to a new time zone after travel. This adjustment leads to a number of side effects.

Generally speaking, the greater the number of time zones you cross the more severe the jet lag will be. So if you travel across three time zones, you’ll experience less discomfort than if you travel across 12.

Follow along as we discuss what jet lag is, why it happens, and how to avoid it.

Jet Lag Causes

Jet lag is primarily caused by the body having difficulty adjusting to a new local time. Light and dark play a crucial role in the body’s patterns of self-regulation. However, there are other causes that can contribute to the effects of jet lag.

The Sleep/Wake Cycle

As previously mentioned, light patterns regulate the release of melatonin in the brain. Melatonin plays a large role in establishing feelings of wakefulness and sleepiness. For most people, darkness triggers a release in melatonin while bright light drastically reduces the amount of melatonin in the brain. As melatonin is released, core body temperature drops. When melatonin is not present, body temperature rises and leads to greater alertness.

Traveling to different time zones means a person will experience bright light at different times of day. These light patterns confuse the body. If you travel to a place twelve time zones (12 hours) away from you, the night/day cycle would be exactly the opposite of where you were before. Thus, your body could confuse early evening with the dawn, for example. This can leave you feeling wide awake while others are going to sleep or vice versa.

Generally speaking, the longer the flight, the more severe jet lag will be. This appears to be especially true while flying east. Flying east effectively shortens the day for the traveler, which the body has a harder time adapting to. The natural body clock is slightly longer than 24 hours, which means it’s easier to lengthen it than to shorten it.

The Air in an Airplane

Another common but less frequently cited cause of jet lag may simply be dehydration. The air inside an airplane is considerably drier than the air at ground level. Since you lose water with every breath, you lose more while on a long flight than you would if you weren’t flying. Dehydration can lead to headaches, impaired cognitive function, and an overall feeling of discomfort.

Similarly, the air in an airplane is at a lower pressure than it would be at sea level. Specifically, an aircraft at a typical cruising altitude of 36,000-40,000 feet has the equivalent air pressure of land at 6-8000 feet. This pressure difference leads to less oxygen reaching the brain, which can cause mild hypoxia — or lack of oxygen. Mild hypoxia can lead to changes in mood.

Changes in pressure over the ascent and descent of a flight cause gases to expand and contract, including those inside your body. A person suffering from abdominal cramps or a sinus or ear infection would be keenly aware of this situation. These expansions and contractions can lead to discomfort, which is usually mild but can be severe depending on the extent of the illness.

Jet Lag Symptoms

Upsetting the internal clock, or body clock, can lead to a number of unpleasant symptoms all too familiar to travelers. The symptoms of jet lag can include sleep problems, impaired mental function, headaches, gastrointestinal discomfort, and more.

Sleep Problems

Perhaps the most common symptom of jet lag is disturbed sleep. The body’s circadian clock is naturally tied to the time zone you’ve been in. Patterns of light exposure regulate the release of the hormone melatonin from the pineal gland in the brain.

Melatonin is one of the brain chemicals responsible for regulating the body’s sleep/wake cycle. Experiencing light at times the body isn’t used to can essentially confuse the body into thinking it’s a different time of day than it really is.

This leads to the sleep disturbances jet lag is known for. These disturbances can appear as excessive sleepiness, sleep deprivation, insomnia, or an otherwise imbalanced sleep schedule.

Impaired Mental Function

Many sufferers of jet lag report impaired mental function as a result. This can be tied to the aforementioned sleep problems. Healthy sleep patterns and a regular sleep/wake cycle help keep a person’s brain sharp. On the other hand, disrupted sleep can lead to “brain fog” due to the imbalanced release of sleep hormones as well as a lack of sleep.

Gastrointestinal Problems

Because digestion is closely tied to the body’s biological clock, a disturbance to that clock can lead to digestive issues. Disturbed sleep patterns can lead to constipation, diarrhea, or general digestive discomfort.

How to Avoid Jet Lag

Jet lag can be unpleasant, but fortunately there are steps you can take to reduce its effects. These steps can take place before, during, and after the flight.

Before the Flight

If you’re taking a long flight and you have time to prepare for it, you can help your body adjust to the destination time zone before you even take off.

For example, if you’re flying from the United States to Europe, you can begin waking up and going to bed slightly earlier every day for several days in a row. You can also adjust your meal times to be slightly earlier to help train your body. This will help you be pre-adjusted to normal sleep times when you arrive, making insomnia and daytime sleepiness less severe.

During the Flight

Losing sleep or sleep quality during long flights is common. This loss can be simply due to environmental factors: light, noise, and uncomfortable seating can make sleeping difficult.

Simply using earplugs and wearing an eye mask can increase the quality of the sleep you do get aboard an airplane. Rather than being disturbed by environmental factors, these can at least help you get good rest to stave off the worst effects of travel fatigue.

Because airplanes have drier air than most people are used to, it’s a good idea to drink plenty of water to remain hydrated throughout the flight.

After the Flight

There are a few steps you can take after a flight to help yourself acclimate to your new time zone. Ideally, these will help make your jet lag experience as short-term as possible.

Time Your Light Exposure

Research suggests that timing when you’re exposed to bright light can help you adjust more quickly to your new time zone. The time when you want to see bright light depends on which direction you travel. If you’re traveling westward, try to get bright light in the evening. Conversely, try to get bright light in the morning if you’re traveling eastward.

You should only need to do this for a few days in order for your body to adjust. As a rule of thumb, the body needs around one day to process each time zone crossed, though this appears to diminish with the number of zones crossed. Crossing twelve time zones would not necessarily have double the effect of crossing six.

If you can’t avoid bright light at the times you don’t want it, sunglasses can help cut down on the amount of light that reaches your eyes. As simple as that sounds, it can play an important role in helping you adjust.

Frequently Asked Questions

Can You Get Jet Lag from a 3-Hour Flight?

Absolutely, though it likely won’t be as severe as it would by crossing more time zones. However, the effects can be acute nonetheless.

Imagine a business traveler is going from California to New York. This business traveler needs to be awake at 7 a.m. in New York for a meeting. However, to the traveler’s body, 7 a.m. feels like 4 a.m. — a time when that person would normally be asleep. Similarly, they would also have to go to bed 3 hours earlier than they normally would, and may struggle to sleep. This can lead to sleep deprivation and is a classic example of jet lag.

Can Jet Lag Last Longer Than a Week?

Yes, it can. The length of jet lag depends largely on the number of time zones crossed and the direction traveled. Generally, traveling eastward leads to greater jet lag than traveling west.

A person’s age can also play a role in jet lag recovery. Older adults tend to need more time to recover from jet lag than younger people. Similarly, people in good physical shape tend to adjust more quickly to time zone changes than others.

By the end of a week, most symptoms of jet lag should have disappeared. In extreme cases, it may take up to two weeks.

Are Jet Lag and Shift Work Disorder Similar?

Yes, they are similar, especially when it comes to disturbed sleep. When a person has to work a schedule of constantly changing shifts that overlap with their naturally established sleep times, the results can be profound. A person can experience insomnia, excessive sleepiness, difficulty focusing or maintaining mental clarity, and mood changes. Shift work disorder and jet lag overlap in many ways.

Can Light Therapy Help With Jet Lag?

In the event you can’t control the times at which you get light — for example if you’re in a cloudy place or a place that’s dark in the winter — light therapy can be useful. Light therapy relies on lights that mimic natural sunlight. These lights are usually used to treat Seasonal Affective Disorder but they are also valuable tools for combating jet lag.

Those traveling westwards — from the US to China, for example — could use a bright light two hours before their normal bedtime while delaying their actual bedtime by two hours. This can incur a circadian shift that will be beneficial upon landing, since the person will already be more adjusted.

Those traveling eastward would need to do the opposite. Using light therapy for 2-3 hours in the morning while pushing bedtime one hour earlier can help acclimate to the change eastward.

Can Diet Play a Role in Combating Jet Lag?

There isn’t much evidence suggesting a healthy diet can reduce jet lag. However, high-protein foods are associated with wakefulness and high-carbohydrate foods are associated with sleepiness. You may try adding each to your diet at appropriate times to help you set your circadian rhythm on track.

Can Exercise Help Jet Lag?

Getting exercise, especially in the morning, can help reduce the effects of jet lag. Exercise raises the body’s core temperature, which leads to greater alertness and mental clarity. Exercising in the morning leads to a natural drop in body temperature at night.

Exercise hasn’t been shown to adjust the body’s circadian rhythm. However, getting quality exercise improves overall sleep quality. Since poor sleep quality is one of the main signifiers of jet lag, improving the quality will help reduce the effects of jet lag.


To sum up, jet lag is the result of traveling across multiple time zones. The further you travel, the more intense the jet lag is likely to be.

Jet lag leads to unpleasant sleep, cognitive, and health-related symptoms. These are short-term and generally disappear within a week. You can take some steps before, during, and after the flight to help prevent and alleviate the effects of jet lag.

Preparing yourself for a different time zone, timing light exposure, and remaining hydrated are some of the simplest things you can do to minimize jet lag. Making sure you get quality sleep on the flight can help as well.

Long-distance airplane travel is more common than ever, so jet lag is affecting more people than ever before. This trend seems unlikely to abate. However, given the convenience and accessibility of modern air travel, jet lag seems like a small price to pay to be able to reach the world’s most far-flung destinations.

This article is for informational purposes and should not replace advice from your doctor or other medical professional.

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