The Facts

Jet lag occurs when there's a mismatch between the time of a person's internal clock and the events affecting that person as a result of rapid travel between different time zones.

Jet lag can make travellers fatigued when they want to be alert, or can keep them from getting a good night's sleep, depending on whether they have travelled "forward" (eastbound) or "backward" (westbound) in time.


You don't experience jet lag from flying between the north and south. It is brought on only by flying a long distance (at least two time zones) going east or west. One may feel unwell getting off a plane from Toronto to Miami, but that's not jet lag - it is the fatigue that comes naturally with travel.

We all have an internal timekeeping system (the circadian clock) that's centred in the hypothalamus, a part of the lower brain. The hypothalamus receives signals from the eyes, telling it whether it's light or dark. According to this information, the hypothalamus tells the nearby pineal gland to secrete or stop secreting a hormone (called melatonin) that governs wakefulness and sleepiness. Melatonin is secreted when it's dark. The more melatonin in your system, the sleepier you are. Research has shown that turning on the lights at night can immediately stop melatonin production.

When we fly across time zones, we enter a world in which everything is happening at the wrong time. The hypothalamus will pick up the new light cues and reset the clock, but it usually takes a day or two. This interval is known as jet lag.

Jet lag is worse when travelling east than when travelling west. Research studies with people who are blind and people who have been isolated from daylight shows that the natural day of the body clock is actually a bit longer than our day by the clock, averaging about 25 hours. This is why so many people find it easier to stay up late than to go to bed early. It is also why eastward travel causes more trouble for the body clock.

The body can readjust by about 90 minutes a day going backwards; that is, one can easily go to bed 90 minutes later each night for a few days. The body can only adjust about 60 minutes forward a day. Therefore it takes about 2 days to adjust to 3 hours of westward travel, but 3 days to adjust to 3 hours of eastward travel.

Symptoms and Complications

The primary symptom of jet lag involves the feeling that everything is happening at the wrong time. Meals and bedtime come too early or too late, depending on whether one has gone east or west. With minor shifts of 2 hours or less, travellers probably won't even notice the effect. They start to adjust as soon as they land, but it takes a day or two, sometimes longer, depending on the distance travelled and number of time zones being crossed.

The most common physical symptoms of jet lag include:

  • apathy
  • daytime sleepiness
  • difficulty concentrating
  • fatigue
  • impaired judgment
  • insomnia
  • irritability
  • restless sleep (sometimes with frequent awakenings)
  • upset stomach
  • diarrhea or constipation

Symptoms such as stuffy nose, aching muscles, swollen ankles, headache, and nausea are usually due to flying and not to jet lag. These symptoms usually disappear soon after landing, which is when jet lag is just beginning.

Jet lag is usually a minor nuisance, but it is associated with some risks. Women who fly a great deal, especially flight attendants, often find that their menstrual cycle is disrupted. The symptoms of peptic ulcer disease can also be made worse by jet lag. This is because the stomach releases acid when the brain thinks it's mealtime. If there's nothing in the stomach, the acid is more corrosive.

People who take insulin for diabetes should talk to their doctor about slowly changing their insulin schedule before travelling across several time zones. Carrying a glucose monitoring device (to measure the amount of sugar in the blood) and using it frequently is especially important under these circumstances.

Treatment and Prevention

You're best off adjusting to the new time as soon as possible. If your schedule permits, it may be useful to begin the time shift even before departure. For 2 or 3 days before departure, go to bed a little earlier or later each night. Go to bed a little earlier if you're travelling east, and go to bed later if you're travelling west.

Some people take melatonin* supplements for jet lag. Recommendations on how to take melatonin vary. In general, melatonin may be taken at an appropriate dose (between 0.1 mg and 10 mg) at bedtime for a few nights starting the day you arrive. If you are traveling eastbound, you may begin to take melatonin at bedtime for a few days before departure. Ask your health care provider when you should start taking melatonin, at what dose, and for how long.

There are studies showing that melatonin can help minimize jet lag, but none prove it is safe to take for long periods of time. Some experts worry that routinely taking this hormone in pill form may reduce the ability of the pineal gland to produce your own internal supply of melatonin. People who travel a great deal and use melatonin frequently are running unknown risks. In most instances, jet lag isn't serious enough to justify this type of risk. Talk to your doctor if you have concerns about melatonin.

If you choose to try melatonin, ensure that the product you buy has a natural health product (NHP) number. This will ensure that the product meets Health Canada's standards of safety and quality.

Recent studies show that changing one's exposure to outdoor light may improve jet lag considerably. This is because sunlight affects the stimuli (zeitgabers) to the eye, which then affects pineal gland. You can also buy light boxes that can be used when outdoor light is not available. It's a good idea to talk to a health care professional about whether light boxes are right for you and how to use them most effectively.

For eastbound travel crossing more than six time zones, exposure to afternoon light (whether or not the sun is shining) is helpful. For travel crossing less than six time zones, morning sunlight is useful. The opposite is recommended for westbound travel.

Some business travellers use a very short-acting sedative medication to sleep on aircraft, thus reducing the risk of jet lag. Ask your doctor whether this is a good option for you.

Other suggestions to reduce the impact of jet lag while travelling include:

  • drinking plenty of water
  • eating small meals frequently and choosing lighter foods like fruit and vegetables
  • ensuring you get enough sleep before you leave - a sleep deficit or "debt" will make jet lag worse
  • limiting or avoiding alcohol and caffeinated drinks
  • trying to nap whenever you feel sleepy
  • wearing loose, comfortable clothing
  • walking around the airplane cabin whenever possible


*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.

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