Jet Lag explained: how to tackle jet lag if you're jetting off this summer

Air Canada aeroplane.. flights across the Atlantic are prone to causing jet lag

As millions of people prepare to travel during the summer holidays, many will experience the familiar frustration of arriving somewhere exciting, only to feel exhausted, wide awake at 3am, or unable to concentrate during the day.

You can travel across the world in less than a day, but your internal rhythms will get left behind. Your brain knows you have landed somewhere new, but your body may still think it is bedtime, breakfast time, or the middle of the night. The result is a temporary mismatch between your internal rhythms and the outside world.

Understanding what is happening inside your body gives you a much better chance of adapting quickly and enjoying your trip.

What is jet lag?

Every cell and system in your body is programmed to follow a roughly 24-hour cycle known as a circadian rhythm. These internal rhythms help coordinate:

• when you feel alert or sleepy

• when hormones are released

• when your body temperature rises and falls

• when your digestive system is most active

• how your immune system functions

• how your brain processes information

Your circadian rhythms are controlled by a “master clock” in the brain, located in an area called the suprachiasmatic nucleus. This clock receives information from the outside world, especially light, to keep your internal timing aligned with the 24-hour day.

When all your internal rhythms are aligned with each other and the local light-dark cycle of the sun, everything works efficiently, and you sleep at night and feel alert during the day. When you rapidly travel across three or more time zones, some parts of your body adapt more quickly than others. The resulting 'circadian de-synchrony' results in the symptoms of jet lag.

How can jet lag affect you?

When most people think of jet lag they think about feeling sleepy during the day, or not being able to sleep at night. In fact, jetlag disrupts more than 1,000 genes in the body  and virtually every system in the body can be affected. 

The symptoms may include:

• Difficulty falling asleep, or staying asleep

• Lack of energy

• Feeling generally unwell, headaches, dizziness

• Irritability, and a worsening of existing mood problems

• Stomach and GI upsets, changes in appetite, nausea, constipation, irritable bowel symptoms

• Cognitive problems, including poor concentration and memory lapses 

• Parasomnias, such as sleep walking, sleep talking and sleep paralysis

• In rare cases, severe jet lag has also been linked to seizures 

How long does jet lag last?

As a rule of thumb, it takes about 24 hours for your internal rhythms to adjust for every hour of time zone that you have crossed. However, there is a lot of individual variation. You will find it easier to adjust if you start your journey well rested, whereas pre-existing fatigue and stress can interfere with the rate of recovery. 

Why is flying east harder than flying west?

You may have heard the phrase: “West is best, east is a beast.” 

Most humans naturally have an internal circadian rhythm that is slightly longer than 24 hours when left in complete darkness, often around 24 hours and 15 minutes. This means our bodies are naturally a little better at extending the day than shortening it. Flying west does exactly that.

For example:

If you fly from London to New York, your day becomes longer. Your body needs to delay sleep and stay awake for longer. That is generally easier than asking your body to suddenly fall asleep earlier.

Flying east requires the opposite. If you fly from New York to London, your day becomes shorter.

Your body needs to advance its internal clock and behave more like an early bird.

That is why many people struggle more with eastward travel.

The most powerful tool for beating jet lag: light

Light is the strongest signal your body has for your internal clocks.

Light enters the eye and sends signals to the brain’s master clock, helping sync your circadian rhythms with your environment.

Bright light promotes alertness and helps shift your body clock.

However, timing matters. The same light exposure can shift your body clock in different directions depending on when you receive it. This is why simply saying “get lots of sunlight” is incomplete advice. The best timing depends on whether you are trying to set your internal clock earlier or later.

If you are flying east: become more of a morning person

Flying east means you need to advance your body clock. Your goal is to shift your clocks onto an earlier timezone.

Before travelling:

• Try going to bed slightly earlier for a few days before departure.

• Wake slightly earlier if possible.

• Seek bright light in the morning.

After arrival:

• Get outside in natural light early in the day.

• Eat meals according to local time.

• Avoid bright light late in the evening if you are struggling to fall asleep.

If you are flying west: become more of a night owl

Flying west means you need to delay your body clock.

Before travelling:

• Gradually move bedtime and wake time later if possible.

• Allow yourself to sleep slightly later.

After arrival:

• Evening light exposure can help delay your internal clock.

• Avoid going to bed too early simply because you are tired.

• Aim to stay awake until a reasonable local bedtime.

For frequent travellers or those crossing many time zones, apps such as Timeshifter can create personalised schedules based on your itinerary and desired adjustment.

How to prepare before your flight?

1. Protect your sleep before travelling

A common mistake is beginning a holiday with a sleep deficit. Late-night packing, early flights and travel stress can mean your body is already struggling before you leave.

Where possible:

• pack in advance

• create a checklist of everything you need to remember

• avoid unnecessary last-minute stress

• prioritise sleep in the days before departure

Think of sleep as preparation, not something you catch up on afterwards.

2. Choose your flight time strategically

A 7am flight might sound convenient but it could mean waking at 4am, travelling while sleep deprived, and arriving already depleted.

If you have flexibility:

• consider flights that allow you to arrive in the afternoon or evening

• avoid compressing your sleep unnecessarily

• give yourself time to adjust before important commitments

  
  

Should you change to destination time during the flight?

Generally, yes. Changing your watch when you board can help your brain start adapting.

Try to align:

• sleep

• meals

• caffeine timing

with your destination schedule where practical.

However, do not panic if you cannot sleep exactly when you “should”. You cannot force sleep. Travel is stimulating, unfamiliar and often stressful. If you cannot sleep, resting quietly with your eyes closed still provides some recovery.

How can you sleep well on a plane?

Sleeping upright in a noisy, bright environment is difficult because humans are designed to sleep lying down in a familiar, safe, comfortable place.

A few simple strategies can help:

Create darkness

Bring:

• an eye mask

• sunglasses to wear before your departure

• comfortable clothing that blocks light

Darkness is a powerful cue for your brain that it is time to sleep.

Reduce noise

Consider:

• ear plugs

• noise-cancelling headphones

• calming music or familiar audio

  
  

Make yourself comfortable

A window seat can help because you can lean against the side of the plane without being disturbed. Layers are useful because cabin temperatures can fluctuate. A comfortable hoodie can double as a way of blocking light and creating a familiar sense of comfort.

Be careful with alcohol

Alcohol may make you feel sleepy, but it reduces sleep quality and can leave you feeling more dehydrated. It is not a sleep aid.

Should you nap after arriving to help jet lag symptoms?

Sometimes. The goal is to avoid a long daytime sleep that makes it harder for your body clock to adjust. Short naps of around 20 minutes are less likely to cause sleep inertia, the groggy feeling after waking.

Why do you feel tired after travelling, even without jet lag?

You can feel exhausted after travelling even if you have not crossed time zones. This is because travel itself is demanding. Factors include:

• early starts

• airport stress

• uncertainty

• dehydration

• sitting still for long periods

• unfamiliar environments

• disrupted eating patterns

There is also something called the first night effect. When you sleep somewhere unfamiliar, your brain can remain slightly more alert, almost as if it is monitoring the environment for safety. This often means sleep is lighter during the first night away. It is a normal protective response.

• To make it easier to sleep in a new environment, try to repeat the same wind down routine that you use at home. A warm bath or shower, reading a familiar book, or meditation can help to detach from the excitement of the day, and get the mind and body ready for sleep. 

• Take a few things which are familiar from home to reduce the first night effect - favourite pyjamas, a book, photos, or even a pillow.