Virtual Medical Centre

Jet Lag

• What is jet lag?
• What causes jet lag?
• Who gets jet lag?
• Symptoms of jet lag

What is jet lag?

Jet lag, also known as circadian dysynchronism or flight dysrhythmia, is a temporary condition that arises as a result of rapid air travel across multiple time zones. It is characterised by symptoms such as disturbed sleep patterns, fatigue, insomnia and irritability, which develop because of the body’s inability to adapt to the new time zone.

Causes of jet lag

Jet lag occurs when there is a disturbance in the synchronisation that exists between the body’s internal clock (circadian rhythm) and the external environmental rhythms. The internal body clock has a natural 24 hour routine that works in sync with environmental cues (also known as zeitgebers, or ‘time givers’) such as daylight to control the sleep-wake cycle. It also influences body temperature, blood pressure, bowel habits, and levels of hormones and glucose in the blood. When travelling across time zones, the natural rhythms of the body that are synchronised with the day-night cycles of the environment cannot adjust instantly. As a result, the brain may trigger activities that the body may not be prepared for, leading to the symptoms of jet lag.

Melatonin is a hormone produced by the pineal gland in the hypothalamus of the brain. Melatonin plays a key role in jet lag and in mediating body rhythms. The internal body clock is a localised group of cells, located in the hypothalamus, which have receptors to melatonin. Melatonin is released in response to darkness and promotes sleep. Daylight inhibits melatonin secretion, thereby encouraging daytime activity.

Not everyone experiences jet lag and individual experiences can vary widely. Additionally, the intensity of jet lag experienced varies with the number of time zones crossed and the direction of travel. Most people feel the effects of jet lag after crossing at least three time zones.

The direction of travel also influences the severity of jet lag experienced. Travellers flying east experience the most problems and require the longest time to adapt, compared to those flying west. It is easier for the body to readjust when travelling west because of the gain in time, rather than travelling east, when time is lost. Travelling eastward can result in difficulties falling asleep and rising in the morning, while westward travel is associated with early evening sleepiness and premature awakening. Flying north or south usually does not cause jet lag, as you are flying within the same time zone.

Who gets jet lag?

Almost anyone can experience some or all of the symptoms of jet lag. The intensity can vary from person to person. There are some people who experience minimal disruption to their natural patterns, whereas others take several days to readjust. Those aged over 50 are most vulnerable. 

The symptoms of jet lag are worse when more time zones are crossed. There are some factors which can make jet lag worse, such as dehydration, lack of sleep, drinking alcohol and stress.

Symptoms of jet lag

The symptoms of jet lag are temporary and may last several days. Readjustment usually takes about one day per time zone crossed.

Symptoms include:

• Insomnia
• Fatigue
• Nausea
• Headache
• Irritablity
• Poor concentration
• Clumsiness
• Decreased alertness in the daytime
• Difficulty with memory
• General weakness
• Dizziness
• Difficulty sleeping and maintaining sleep at night
• Gastrointestinal disturbances (e.g. diarrhoea, constipation, indigestion, loss of appetite)
• Deterioration of performance in physical and mental tasks

Although jet lag is temporary, it can cause some long term consequences for frequent travellers (e.g. flight crew). Irregular menstrual cycles are frequently reported by women.

Jet lag can be disruptive for business travellers and holiday-makers. It can also affect performance and jeopardise training in athletes. A causal link has been made between jet lag and accidents. This is especially important for pilots, who may be prone to making errors as a result of reduced mental and physical performance.