Jet Lag
In this condition factsheet:
The Facts on Jet Lag
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.
Causes of Jet Lag
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 of Jet Lag
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.
