Jet lag, medically referred to as desynchronosis, is a physiological condition which results from alterations to the body's circadian rhythms resulting from rapid long-distance transmeridian (east–west or west–east) travel on a jet airplane. It is classified as one of the circadian rhythm sleep disorders.

The condition of jet lag may last several days until one is fully adjusted to the new time zone, and a recovery rate of one day per time zone crossed is a suggested guideline. The issue of jet lag is especially pronounced for airline pilots, crew, and frequent travelers. Airlines have regulations aimed at combating pilot fatigue caused by jet lag.

Cause [link]

Jet lag is a chronobiological-related problem^[1], similar to issues often induced by shift work. 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 trans-meridian (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 [link]

The symptoms of jet lag can be quite varied, depending on the amount of time zone alteration, time of day and individual differences. They may include the following:^[2]

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

Jet lag has been measured with simple analogue scales but a study has shown that these are relatively blunt for assessing all the problems associated with jet lag. The Liverpool Jet lag Questionnaire was developed to measure all the symptoms of jet lag at several times of day, and this dedicated measurement tool has been used to assess jet lag in athletes.Waterhous et al., 2002

Management [link]

It is possible to minimize the effects of jet lag by following some basic steps before, during, and after the flight. Full details of these steps can be found in two reviews published in the Lancet^[3]. There is also a position statement from the European College of Sports Science for management of jet lag in athletes^[4].

Before the flight [link]

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.

One tactic is to attempt to partially adapt to the destination time zone in advance. This includes starting the daily routine one hour before or after one normally does during the week before departure. The use of a light box might help speed up the body's body clock adjustment significantly.^[5]

During the flight [link]

One option to counteract jet lag is to break the trip into smaller segments if it is too long and stay overnight at an intermediate destination. Additionally, it may be advisable to adjust sleeping hours on the plane to match the destination time.

Upon arrival [link]

A helpful way to minimize jet lag is to adapt to the local time and eat accordingly. Also, exposure to sunlight during the day is helpful.^[6]

Direction of travel [link]

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.^[7]

It may also be that flights to the east are more likely to require people to stay awake more than one full night 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. 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.

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 [link]

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.^{[citation needed]}

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.^{[citation needed]}

Melatonin [link]

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.^[8]

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 0.3–0.5 mg, to be taken the first day of traveling. Administration of higher doses can cause sleepiness, lethargy, confusion, and decreased mental sharpness.^[6]

A position statement on the use of melatonin for alleviating jet lag in athletes was published in the British Journal of Sports Medicine^[9]. Melatonin is not recommended for people with the symptoms of severe mental illness, severe allergies, autoimmune diseases, immune system cancers, or pregnant women.^[10]

Light therapy [link]

The body requires approximately one day per time zone to adjust its circadian rhythm.^{[citation needed]} A manufacturer of light-therapy lamps claims that using light therapy can speed this process up to one hour per time zone when used at the correct time, combined with avoiding light during specific periods.^[11]

The presence of low-level light at night accelerates recovery rates in both east- and west-travelling hamsters of all ages by 50%; this is thought to be related to simulation of moonlight.^{[12] [13]}

Fasting [link]

A 2008 animal study^[14] suggested that lack of food helps to override the light-controlled circadian body clock. One of its authors suggested in a statement^[15] that "a period of fasting with no food at all for about 16 hours is enough to engage this new clock. [...] The neat thing about this second clock is that it can override the main clock [...] and you should just flip into that new time zone in one day". One approach to implement this would be to eat nothing on the plane and fast until it is breakfast time at the destination.

Viagra [link]

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.^[16] However, this use has not been tested in humans and is considered an off-label use by the drug's manufacturers.

See also [link]

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

References [link]

External links [link]

• British Airways Jet Lag calculator
• Body Clock Jet Lag calculator