What is Jet Lag?

Mark Dobson
Jun 9
3 min read

Jet lag is a temporary sleep disorder that arises when an individual's circadian rhythm becomes desynchronised from the local time at their destination after traversing multiple time zones. Crossing three or more time zones may substantially disrupt circadian alignment, causing jet lag if prompt adaptation to the new time schedule is not achieved. [1-2].

What are jet lag symptoms?

severe fatigue
insomnia
daytime sleepiness
poor concentration

Does direction of travel affect jet lag?

Research indicates that jet lag is typically worse when travelling east rather than west. Westward journeys effectively extend your circadian rhythm, as time zones move backwards (for instance, 18:00 in London is 13:00 in New York), which tends to make recovery from jet lag quicker than after eastward journeys. This is because our bodies naturally find it easier to adjust to longer days than to shorter ones, making adaptation to westward travel simpler. [1]

What factors influence Jet Lag?

The severity and duration of jet lag symptoms can vary among individuals and are influenced by several factors, including:

Number of time zones crossed
Direction of travel (eastward or westward)
Individual susceptibility (such as age, stress, gastrointestinal disorders and mental health conditions)
Presence of pre-existing sleep disorders
Presence of pre-existing medical conditions [3]

What can help?

Resetting the Internal Clock

After reaching your destination, your body clock may be out of sync with the local time. Adapting to the new time zone can be challenging since bodily processes adjust at different speeds (your circadian rhythm usually needs 1 to 1.5 days per time zone crossed to adjust). Resetting your internal clock helps lessen jet lag and eases your transition. [4]

For short travel stays (of three days or less):

Continue sleeping and eating at your usual times to keep your body’s rhythm steady when traveling briefly. Sticking to your regular schedule can help prevent fatigue and confusion, making time zone adjustment unnecessary for short trips.

For longer travel stays:

Get plenty of sleep before your trip to minimise 'sleep debt' and reduce jet lag. If you usually lose sleep due to pre-travel tasks, aim for extra rest in the days leading up to your departure.
To help your body adjust before travel, gradually change your bedtime to match your destination’s schedule. Shift sleep and wake times by an hour each day—earlier for eastbound trips, later for westbound ones.
Set your watch to your destination’s time when you board the flight and adjust your routine—such as eating and sleeping—to match. This helps your body adapt faster and can reduce jet lag. [5]

Jet lag or chronic insomnia?

If you are struggling with chronic insomnia consider some sleep therapy. Cognitive Behavioural Therapy for Insomnia (CBT-I) is widely recognised as the "gold standard" first-line treatment for chronic insomnia, as recommended by leading medical bodies such as the American College of Physicians . This structured, non-pharmacological therapy works by targeting and changing problematic behaviours and thoughts related to sleep. Notably, CBT-I has demonstrated a 70–80% success rate in improving sleep, according to clinical studies published by the American College of Physicians, which lends strong credibility to its effectiveness.