Jet lag, also known as time zone change syndrome or desynchronosis, occurs when people travel rapidly across time zones or when their sleep is disrupted, for example, because of shift work.

It is a physiological condition that results from a disruption in the body’s circadian rhythms, also known as the body clock. It is seen as a circadian rhythm disorder.

Symptoms tend to be more severe when traveling eastward compared with westward.

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Air travel can cause jet lag, especially long-haul flights going from west to east.

Jet lag can occur when sleep-wake patterns are disturbed. A person may feel drowsy, tired, irritable, lethargic, and slightly disoriented.

It can result from traveling across time zones or from doing shift work.

The more time zones a person crosses in a short period, the more severe the symptoms are likely to be.

Jet lag is related to a disruption in activity and a lack of synchronization in the brain cells of two parts of the brain.

The older a person is, the more severe their symptoms will normally be, and the longer it will take for their body clock to get back into sync.

Children usually have milder symptoms, and they recover faster.

To understand jet lag, we need to know about circadian rhythms.

What are circadian rhythms?

Circadian rhythms, or the body clock, are 24-hour cycles in the biochemical, physiological, and behavioral processes of our bodies. They regulate daily activities, such as sleep, waking, eating, and body temperature regulation.

The body clock and the brain

Jet lag appears to involve a disruption in two separate but linked groups of neurons in the brain. These neurons are part of a structure called the suprachiasmatic nucleus (SCN). The SCN is located below the hypothalamus at the base of the brain.

One of these groups of neurons is associated with deep sleep and the effects of physical fatigue. The other group controls the dream state of rapid eye movement (REM) sleep.

The group of neurons involved in REM sleep finds it harder to adjust to the new cycle, and the two groups become out of sync.

What puts the body clock out of synch?

The body clock is driven by an internal time-keeping system, but it is affected by external environmental factors, such as the light-dark cycle of night and day.

When the body clock gets out of synch and needs to be reset, jet lag results.

Traveling across different time zones and going through daylight and darkness cycles that are different from the rhythms we are used to can cause our body clock to get out of synch. Other causes include shift work and some sleeping disorders.

Jet lag affects patterns of sleeping and waking and of eating and working.

Hormone regulation is key to body clock synchronization. When jet lag happens, hormone levels get out of sync with the environment. Body temperature also varies according to the body clock.

Jet lag will continue until all these factors can respond properly to the new environment.

Why is it harder to travel from west to east?

When travelling eastward, symptoms feel more severe, because our bodies have less time to recover. Travelling westward adds hours to our days whereas travelling eastward reduces them. This means that our bodies have less time to adjust and synch up with a circadian rhthym when flying east.

Traveling from north to south or south to north can cause additional problems, as the seasons are different.

However, for jet lag to occur, there must be an east-west or west-east movement. Flying directly south from Chicago to Santiago in Chile may cause discomfort, but it will not lead to jet lag.

In addition, jet lag does not usually occur after crossing just one or two time zones. The more time zones one crosses, the worse the symptoms may be.

Alcohol and caffeine

The World Health Organization (WHO) points out that drinking alcohol or caffeine during or before the flight may worsen symptoms. For one thing, these can both add to dehydration. The air inside an airplane cabin is drier than natural air at ground level, and this too can worsen symptoms.

Drinking alcohol increases the need to urinate, which can disrupt sleep. Also, while alcohol often induces sleep, the quality of sleep will be lower. In addition, the hangover effect of alcohol can worsen the effects of jet lag and travel fatigue.

Caffeine can also disrupt sleep patterns. It is best to drink water while flying.

Other factors that can worsen symptoms include stress and spending a long time sitting uncomfortably.

People who can stretch out or lie down and sleep during a flight are less likely to experience jet lag.

Altitude sickness, oxygen, and dehydration

There may be a link between environmental levels of oxygen and jet lag.

The pressure in an airplane’s cabin is lower than the pressure at sea level. This means that the amount of oxygen reaching the brain may be reduced when people are flying.

This can lead to lethargy and a higher risk of more severe jet lag symptoms. Researchers have suggested that oxygen modulation therapy could be used to reduce the effects of jet lag.

Researchers have found that people traveling on commercial flights face changes in air pressure that can lead to lower levels of oxygen saturation. This can result in discomfort after 3 to 9 hours, and symptoms that resemble those of altitude sickness.

Symptoms of jet lag vary.

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Sleep problems are a common effect of jet lag.

They include:

  • sleep disturbances, insomnia, lethargy, and fatigue
  • a heavy, aching head
  • irritability, confusion, and difficulty focusing
  • mild depression
  • loss of appetite
  • a dizzy, unsettled feeling
  • gastrointestinal disturbances, such as diarrhea or constipation

Factors that affect which symptoms occur and how severely include the number of time zones crossed and the individual’s age and state of health.

A range of actions can be taken to help reduce symptoms.

There is currently no treatment for jet lag, but some lifestyle adjustments can help minimize the symptoms.

Physical fitness and health: People who keep physically fit, rest properly, and eat a well-balanced diet appear to have fewer and less severe symptoms than someone who is less fit.

Controlling underlying medical conditions: Existing medical conditions, such as lung disease, heart disease, or diabetes, can make symptoms worse. Ask your doctor for advice before making a long-haul trip.

Other tips include:

  • choosing flights that arrive in the early evening local time, so that you can aim to sleep around 10.00 p.m.
  • preparing for a long flight eastward, by getting up and going to bed early for several days before, and for a westward flight, get up and go to bed later
  • changing your watch to the destination time zone as soon as you board the plane
  • keeping active during the flight by doing exercises, stretching, and walking along the aisle
  • using an eye mask and ear plugs and aim for strategic napping. Try to sleep when it is night-time at your destination, and sleep for 20 minutes at a time at other times, to reduce sleepiness
  • drinking plenty of water during the flight, and avoiding alcohol and caffeine, to minimize dehydration

On arrival:

  • Avoid heavy meals or strenuous exercise.
  • Spend time outdoors preferably in sunlight.
  • Sleep at a “normal” time for the destination time zone.

The sooner a person can adapt to the local timetable, the sooner the body clock will adapt to the new environment.

People who travel regularly for work should make sure they get regular exercise.

Light adjustment and melatonin

One study has indicated that wearing sunglasses during part of a long-haul flight may help the body adjust to the new time zone by altering their light patterns.

Researchers investigating the role of melatonin and other hormones in the function of the body clock have suggested that one day, drug therapies may be available for people who experience difficulties due to shift work or jet lag.

Some people already take melatonin as a dietary supplement to help with jet lag, but there is not yet sufficient evidence to confirm its effectiveness.

People who know they are prone to severe jet lag might consider breaking a long journey en route, or traveling overland, if possible.