Jet lag

This article is about the syndrome. For other uses, see Jet lag (disambiguation).

Jet lag
Classification and external resources
ICD-10	G47.2
ICD-9	307.45, 780.50 327.35
MeSH	D021081

Jet lag, medically referred to as "desynchronosis," is a physiological condition which is a consequence of alterations to circadian rhythms; it is classified as one of the circadian rhythm sleep disorders. Jet lag results from rapid long-distance transmeridian (east-west or west-east) travel, as on a jet plane.

The condition of jet lag may last many days, and recovery rates of 1 day per eastward time zone or 1 day per 1.5 westward time zones are mentioned as fair guidelines.

Cause

When traveling across a number of time zones, the body clock will be out of synchronization with the destination time, as it experiences daylight and darkness contrary to the rhythms to which it has grown accustomed: the body's natural pattern is upset, as the rhythms that dictate times for eating, sleeping, hormone regulation and body temperature variations no longer correspond to the environment nor to each other in some cases. To the degree that the body cannot immediately realign these rhythms, it is jet lagged.

The speed at which the body adjusts to the new schedule depends on the individual; some people may require several days to adjust to a new time zone, while others experience little disruption. Crossing one or two time zones does not typically cause jet lag.

The condition is not linked to the length of flight, but to the transmeridian (west-east) distance traveled. A ten-hour flight from Europe to southern Africa does not cause jet lag, as travel is primarily north-south. A five hour flight from the east to the west coast of the United States may well result in jet lag.

Crossing the International Date Line does not contribute to jet lag, as the guide for calculating jet lag is the number of time zones crossed, and the maximum possible disruption is plus or minus 12 hours. If the time difference between two locations is greater than 12 hours, subtract that number from 24. Note, for example, that the time zone GMT+14 will be at the same time of day as GMT-10, though the former is one day ahead of the latter.

Symptoms

The symptoms of jet lag can be quite varied, depending on the amount of time zone alteration. They may include the following:

• Headaches
• Fatigue, irregular sleep patterns, insomnia
• Disorientation, grogginess, irritability
• Mild depression
• constipation or diarrhea

Other symptoms which some may attribute to jet lag, such as nausea, ear aches and swollen feet, may be caused by the mode of travel rather than the time zone change.

Management

It is possible to minimize the effects of jet lag by following some basic steps before, during, and after the flight.

Before the flight

People are advised to get plenty of rest, exercise and follow a healthy diet. When the person is in good shape, it is easier to cope after landing.

Also, it is recommended to visit the doctor to plan a coping strategy for medical conditions that require monitoring, including when to take medications or any other necessary detail.

Another advice is to adapt to the destination time zone in advance. This includes starting the daily routine one hour before or after one normally does from three to four weeks before departure.

During the flight

To avoid dehydration, passengers are discouraged from taking alcoholic beverages and caffeine. Caffeine not only causes dehydration but also disrupts sleeping schedules. On the contrary, the recommendation is to drink plenty of water to help counteract the effects of the dry atmosphere inside the plane.

Passengers are encouraged to exercise their legs while sitting and move around the plane when the seat belt sign is switched off, every hour or two. One option to counteract jet lag is to break the trip into smaller segments if it is too long and stay overnight in some city. And, finally, to adjust sleeping hours on the plane to match the destination time.

Upon arrival

A helpful way to minimize jet lag is to adapt to the local time and eat accordingly, following the meals that correspond. Also, exposure to sunlight during the day is helpful.

Direction of travel

There seems to be some evidence that for most people, traveling west to east is more disruptive. This may be because most people have a circadian period which is a bit longer than 24 hours, making it easier to stay up later than to get up earlier.

It may also be that flights to the east are more likely to require people to stay awake more than one full night in order to adjust to the local time zone. For example, comparing a typical schedule for a traveller flying to the west vs a traveller flying to the east:

• Westbound from London to Los Angeles, VIA BA0279, Jan 29, 2008. Time zone difference 8 hours.

Westbound	Biological clock London local time	Los Angeles local time
Departure	JAN 29 – 10:05	JAN 29 – 02:05
Arrival	JAN 29 – 21:10	JAN 29 – 13:10
Bedtime	JAN 30 – 06:00	JAN 29 – 22:00

• Eastbound from Los Angeles to London, VIA BA0278, Jan 29, 2008.

Eastbound	Biological clock Los Angeles local time	London local time
Departure	JAN 29 – 15:50	JAN 29 – 23:50
Arrival	JAN 30 – 02:00	JAN 30 – 10:00
Bedtime	JAN 30 – 14:00	JAN 30 – 22:00

The first scenario is equivalent to staying up all night and going to bed at 6 a.m. the next day—8 hours later than usual. But the second scenario (eastward) is equivalent to staying up all night and going to bed at 2 p.m. the next day—14 hours after the time one would otherwise have gone to bed. Some sleep onboard may help the situation somewhat.

The Red-eye flight is another eastward scenario, for example flights departing the west coast of the US at midnight (PST/PDT) and arriving on the east coast early in the morning (EST/EDT). Relative to the shorter flight time and the time zones advanced, the body gets less than optimal rest to begin a day of activity.

Remedies

Since the experience of jet lag varies among individuals, it is difficult to assess the efficacy of any single remedy. Gradual adjustment over the course of several days of the onset of sleep while maintaining its regular length of 7–8 hours can reduce fatigue and prevent depression. When the goal is to catch-up with local time (vs. fallback to), this can be aided by avoiding afternoon naps and eating an early and carbohydrates-rich, low-protein dinner.

The presence of low-level light at night also accelerates recovery rate in both east- and west-travelling hamsters of all ages by 50%; this is thought to be related to simulation of moonlight.

Most chemical and herbal remedies, including the hormone melatonin, have not been tested nor approved by official agencies such as the United States Food and Drug Administration. Few studies have tested the use of melatonin for jet lag and have given mixed results, likely because the timing of administration needs to be precise and individualized.

Melatonin

Melatonin is present in the bloodstream naturally in differing amounts according to the time of day. It is produced by the pineal gland in darkness; secretion stops when there is light to the eyes. It plays a key role in the circadian rhythm which regulates various significant body functions.

A 2005 study showed that melatonin was effective in helping people fall asleep at doses of 0.3 milligrams (mg). Then, to treat the jet lag, the recommended dose of melatonin is of 0.3 to 0.5 mg., to be taken the first day of traveling. Administration of higher doses can cause sleepiness, lethargy, confusion, and decreased mental sharpness.

Melatonin is not recommended for people with the symptoms of severe mental illness, severe allergies, autoimmune diseases, or immune system cancers. Neither is it recommended for pregnant women.

Viagra

A recent study in hamsters showed that sildenafil citrate (known commercially as Viagra) aided in a 50% faster recovery from shifts comparable to eastward travel experienced by humans and was effective starting at low doses. However, this use has not been tested in humans and is considered an off-label use by the drug's manufacturers.

See also

• Chronobiology
• Light therapy
• Red-eye flight, an overnight east-bound flight with insufficient time to get fully rested.

References

zh:时差问题