Jet lag

What causes jet lag?

Jet lag is a group of symptoms caused by disruption to the natural rhythms of the body, called circadian rhythm, by moving quickly across the world's time zones. It results from a temporary mismatch between the body's internal clock and the destination sleep/wake schedule.

This can either make it hard to fall asleep, or make you sleepy when you're trying to stay awake. It can also cause dizziness, indigestion, nausea, constipation, altered appetite and mild anxiety.

Before the advent of fast air travel, long journeys were slow enough for us to adjust gradually to different time zones as we travelled. Jet lag occurs when we travel so fast that we 'gain' or 'lose' extra hours more quickly than our body's capacity to adjust allows.

You don't need to travel to get jet lag. Shift work or a series of late nights can have the same effect. This also puts your melatonin and cortisol clocks out of synch with the daylight hours that you need to work to.

If you are travelling over only one or two, or possibly three, time zones, jet lag is not usually a problem. It usually affects people travelling across more than three time zones. So if the time at your destination is more than three hours different to that at the start of your journey, you are likely to experience jet lag. The more the time difference, the greater the problem jet lag is likely to be.

Jet lag only affects people travelling quickly. If you are travelling more slowly, by boat or car, your body clock will be able to adjust gradually.

What are the symptoms of jet lag?

The most common symptoms of jet lag are related to sleep. You may have difficulty getting to sleep at bedtime and struggle to wake up in the morning, or you may be tired long before bedtime and wake up while it is still night and too early to get up.

The effect of this difficulty with sleeping is feeling tired and not being able to function as well as usual. Common symptoms include:

• Tiredness, which can be severe.

• Sleepiness.

• Disturbed and wakeful nights.

• Feeling light-headed or 'spaced out.'

• Feeling jittery, anxious or shaky.

• Having a fine tremor.

• Poor concentration and memory.

• Being less co-ordinated than usual.

• Irritability.

• Low mood and weepiness.

• Homesickness.

• Not wanting to join in normal activities.

• Poorer performance in sports than usual (particularly a problem for athletes).

• Constipation.

• Poor appetite.

• Nausea and indigestion.

Other aspects of travel, such as cabin pressure, can also have an effect on your digestion. Changes in cabin pressure can cause both lack of fluid in the body (dehydration) and bloating, which may contribute to your symptoms.

Complications

Some of the symptoms of jet lag (such as poor concentration, or feeling 'spaced out') may cause problems performing complex (potentially dangerous) tasks, such as driving or operating machinery. You should not drive if you feel you are not functioning normally.

When to see a doctor about jet lag

If you are not recovering from jet lag and your symptoms are causing problems (such as sleep disturbance, disrupted appetite or altered mood - anxiety and depression), you should see your doctor. They can assess your symptoms and suggest how to manage them.

Who gets jet lag?

Risk factors

People who travel frequently, particularly airline pilots and crew, are most likely to have problems with jet lag. Most people who fly very long distances will be affected, particularly if they fly coach class and can't easily manage to sleep on the flight even when they are sleepy.

Jet lag can be a problem for athletes competing in different parts of the world, as it is likely to affect physical performance. It is also a concern for business travellers as it may cloud their thinking for several days.

Do some people get worse jet lag than others?

People vary in their ability to adjust to travel across time zones. Whilst people will take on average one day to correct for each hour, once they have crossed more than three time zones, some people take longer than this.

There is a small subgroup of people whose adjustment is very slow to begin, so that their circadian clock does not initially shift. You may know if you are one of these people, as you may experience worse jet lag than others. If this is the case then consider starting the jet lag preparations detailed here 4-5 days prior to travel, rather than only 2-3 days beforehand.

How long does jet lag last?

The circadian 'clock' is capable of adjusting by 1-2 hours each day without too much difficulty, so that we can accommodate variety in bedtime and getting up times - but adjusting to more than three hours or more can take time - roughly a day for each hour's adjustment. Three hours is borderline - some people will notice it, others will not.

Why does travelling east cause worse jet lag than travelling west?

The principle behind jet lag is that we need a similar amount of quality sleep, in one stretch. It's not easy to make ourselves sleep for extra hours when we travel, so we mainly need to move the sleep time, increasing or reducing our awake time.

Travelling to the west is easier as the brain finds it easier to move its clock back (by delaying release of melatonin and cortisol and sleeping later), than to move it forward (releasing it earlier).

Travelling to the east is harder, because you have to try to go to sleep when you are not tired, and without your body having produced the melatonin that usually helps this happen.

How can I prevent jet lag?

It is possible to avoid jet lag but it needs commitment and advance planning. The main key to these strategies is getting enough quality sleep in the few days before your trip, whilst trying to move your sleep period forwards or backwards.

If you try these strategies for 2-3 days before travel (4-5 days if you are a slow adjuster) then you can 'advance adjust' your circadian rhythm and reduce or even eliminate jet lag.

How do I reduce jet lag when travelling west?

If you are travelling west then you will gain time, so the principle of preventing jet lag is to prepare in advance by convincing your body it is earlier than it is, whilst continuing to get the right amount of quality sleep.

• You won't be able to sleep for longer than usual, so you need to move your sleep period to later.

• Try to stay in bright light in the evening, so that you delay release of melatonin until the new bedtime, and avoid bright lights in the morning, so your brain will think the sun hasn't risen yet.

• Exercising at night will increase your body temperature, which will also shift your clock backwards. Staying up and sleeping in late will help even more.

How do I reduce jet lag when travelling east?

If you are travelling east, then you will lose time, so the principle of preventing jet lag is to convince your body it is later than it is, whilst continuing to get enough quality sleep.

You won't be able to sleep for longer than usual, and your challenge is to move your sleep period backwards and convince your body it is later than it really is. Long-haul flights east from the UK usually dim the lights early to assist you with this.

• Avoid light as much as possible in the evening.

• Go to sleep early, and get plenty of bright light when you wake up.

• It also helps to exercise soon after rising, to increase your body temperature.

• It is possible that taking melatonin may help (see below).

What should I do to ward off jet lag once I reach my destination?

Once you get to your destination use light to assist your body's adjustment to the new time zone - plenty of light (and exercise) in the morning and during the day, and darkness at night.

• Avoid power napping when you're trying to adjust your clock.

• Don't think about the old time zone at all - reset your watch and eat, stay well-hydrated, exercise and sleep in the new zone.

• Avoid alcohol until you feel you have fully adjusted.

How do I get over jet lag when I arrive?

The most effective treatments for jet lag rely on shifting the circadian clock to the new time zone as fast as possible.

If you don't have time to prepare and experience jet lag, it will gradually subside on its own after a few days, as your body clock adapts to the new time zone. There are a number of strategies to help you get over it more quickly:

Ensure good-quality sleep in the darkness

• After arrival at your destination, try to change your schedule to the new time zone as quickly as possible.

• Avoid going to sleep until it is a reasonable bedtime for the new time zone. Then turn all the lights out, and use ear plugs if others have not settled to sleep.

• Set alarms to stop you oversleeping in the morning. When you get up, turn the lights on.

• Avoid caffeine, nicotine and alcohol in the six hours before you plan to sleep as they may interfere with your sleep cycle.

• Prior to going to bed, try to relax. Avoid large meals, heavy exercise and exciting books or films before sleeping.

• Shortwave or 'blue' light is thought to be most important in stopping melatonin being released. Therefore, glasses which block out blue light may help you release melatonin earlier than usual. It may therefore be helpful to wear them for a couple of hours before bed, although more research is needed. This would only be helpful if you are trying to bring forward the time you go to sleep - for example, after travelling east.

Ensure wakefulness when it's daylight

• Warm up in the morning with light exercise and a hot shower.

• If you normally exercise at night, consider switching your routine and exercising in the morning.

• Caffeine-containing drinks such as coffee may help keep you awake until it is a reasonable time to go to sleep.

• Expose yourself to outside natural light as much as possible. This will help your internal clock adjust.

• If you are only in the new time zone for two to three days it may be easier to stay on your original timings. Eat and go to sleep at times that would be normal for you, even if they aren't the right times for the place you are now in. This may not be practical for everybody, as it depends on what you want or need to do while you are away.

• Some people use light boxes or commercial light devices to increase their light exposure. This may be helpful.

Do commercial light devices help with jet lag?

Various commercial light boxes and light devices are marketed for jet lag - many of them are also marketed for seasonal affective disorder (SAD).

• Large boxes are easier to sit in front of, and usually more tolerable.

• Small light boxes and worn devices are more portable.

• Light boxes that can produce blue light, and which use LEDs, may be more effective because the circadian system is most sensitive to blue light.

Several online calculators, apps and devices are available to tell the traveller how and when to use the light, when to seek darkness and to seek normal daylight in the days after travelling.

Do jet lag calculators help with jet lag?

Jet lag calculators are online tools that give you an 'adjustment programme' to try to prepare for international travel. The idea is that you put your travel details into the calculator and it tells you how to adjust your sleeping patterns prior to, and during, travel.

Many of them are based around the use of light devices, some of which are marketed by the makers of the app or calculator.

Some calculators may be based on expecting a faster adjustment than the one hour per day recovery which most researchers agree is typical for most of us. This means that the timetables offered over several days are not always helpful - they may, in other words, give you too much light too soon. Using the light devices before travel, to prepare for the new time zone, is thought to help reduce this problem.

Do coloured spectacles help with jet lag?

The idea of wearing coloured specs on the plane relates to the fact that melatonin production is reduced by the presence of blue light. Coloured specs - they usually look red - filter out the blue light. The idea is that these are worn for a couple of hours before you want to sleep, particularly when travelling east, to try to stimulate your natural melatonin production in order to start to shift your circadian rhythm.

Do sleeping tablets help with jet lag?

There are currently no treatments specifically licensed for jet lag. This is partly because adjusting the sleep-wake cycle is complicated, and affected by travel itself.

We all adjust differently, and the time at which medicines need to be taken in order to make things better rather than worse, differs between individuals and journeys.

Sleeping tablets are often considered by those trying to get back into a sleeping pattern. However, most doctors will advise against this. Sleeping tablets do not treat jet lag; they only mask it because they don't reset your circadian rhythm, they just sedate you.

They are highly addictive and can affect your ability to fall asleep by yourself even after only a couple of days of use. You also may be more irritable, and perform less well, when you wake.

What is the circadian rhythm?

We all have an internal clock, managing our body through day and night. Many of the systems in our bodies are affected by it, including appetite and energy levels, and sleepiness. The normal cycle, of sleeping at night and being alert and active in daytime, is called the circadian rhythm.

All living beings, even plants, have an internal clock. The rhythm is a response to the cycle of daylight and darkness.

There are two main components to our internal clock. These are melatonin (produced by a gland in our brain called the pineal gland) and cortisol, (produced by the adrenal gland, on top of the kidney).

Both affect arousal (alertness), sleepiness, mood, energy level, and body temperature, and both are mainly regulated by an area of the brain called the hypothalamus, a kind of central control zone located at the base of the brain, behind your eyes.

What is melatonin?

Melatonin is one of the main hormones involved in helping you sleep. Melatonin production occurs mainly when it is dark. Bright artificial light, blue light and natural light, can reduce melatonin levels.

Higher melatonin levels are associated with better sleep quality, reduction in depression, and better cognitive performance (this means performance in tasks like attention, reaction time, visual memory and mental maths).

The brain releases melatonin an hour or two before you normally sleep. At the same time body temperature begins to fall, reaching its lowest temperature in the early hours of the morning.

What is cortisol?

An hour or two before expected waking, your body releases cortisol, and then adrenaline (epinephrine). These hormones increase arousal and wakefulness. If levels are high they can make you anxious or uneasy.

Once you have crossed more than three time zones it typically takes the cortisol production pattern one full day to adjust for every time zone crossed. It takes four days to adjust to a four-hour change (even though a two-hour or even a three-hour change can usually be managed without jet lag).

Does taking melatonin help with jet lag?

Melatonin is often suggested and discussed as a remedy for jet lag. It is not a licensed treatment, although it is a tablet form of the natural melatonin hormone which your brain produces. You might imagine, from reading this leaflet, that melatonin would help jet lag. However, the truth is more complicated.

• A wide body of research suggests that melatonin pills do effectively shift the circadian clock and can be a useful tool for reducing jet lag, particularly when travelling east.

• Melatonin is available from health food shops as a dietary supplement.

• However, it is also not yet known what dose should be used, or exactly when melatonin should be taken.

• Some evidence suggests that melatonin can prevent jet lag if taken as part of the advance preparation for jet lag detailed above.

• One possible downside of taking melatonin is that adjusting to a new time zone means adjusting your OWN circadian clock, which means producing your OWN melatonin. Until you do that you won't have adjusted, so even though taking large doses of melatonin can make you sleepy, it's not adjusting your body, and it may actually interfere with your body's own efforts to adjust, simply delaying the jet lag without preventing it.

How do I prevent jet lag in my baby or toddler?

At the best of times, it can be difficult to get your baby or toddler to sleep at the right time, and when you are travelling and everything is strange, worrying, tense or exciting then trying to get them to sleep when you want them to can be an impossible task.

Should I sedate my baby or toddler to avoid jet lag?

Some people try to sedate their children with antihistamine-type sedatives. Unfortunately, this is not a great solution. Only a really high dose of a sedative will make a child sleep when they don't want to - a higher dose than you would want to give for travel.

Lower doses risk making them irritable and drowsy without being sleepy, potentially making them tired and fractious. Worse than this, once the medication wears off they tend to suffer from a 'rebound' agitation which may make them irritable, upset and shaky.

Do what your baby does

The preparations above for jet lag only work if you are free to do them. If you are working around a baby or toddler when you are travelling you will need to try to rest when they rest, and accept the need to be awake when they are awake.

You can help yourself by preparing, as much as you can, before you travel, using others to help you get the sleep you need to try to adjust in advance to the new time zone.

How do I treat jet lag in my baby or toddler?

Helping your baby adjust to a new time zone

When you reach your destination and your child is wide awake, give them breakfast. Their jet lag is telling them it is time for breakfast and you won't be able to convince them otherwise.

Accept that you can't sleep and, if you are tired, just try to be as restful as possible. Read favourite books, give them a warm bath, try not to overstimulate them, but to relax them. Eventually they will need to sleep, but they may hold out longer than you thought possible.

After an interval of 2-3 hours, if they are calm, fed and happy, try a bedtime routine again - pyjamas, quiet and darkness may all signal to your baby or toddler than it's time to sleep. If they sleep then sleep yourself, and try to make sure nobody disturbs them until they've slept it off.

See also the separate leaflet called Travelling to Remote Locations for further advice on travelling with young children.

Dr Mary Lowth is an author or the original author of this leaflet.