How to Beat Jet Lag:
The Science-Based Guide

What is jet lag?

Jet lag is a temporary sleep disorder caused by rapidly crossing multiple time zones. Your body has an internal 24-hour clock (your circadian rhythm) that governs when you feel sleepy, when you feel alert, when your body temperature peaks, and when hormones like melatonin are released.

But jet lag isn't the only thing that can floor you after a flight. The cabin itself takes a physical toll. Here's how to tell which one is actually hitting you.

When you fly from Sydney to London, your circadian clock still thinks it's Sydney time. Your brain expects to sleep at midnight Sydney time, which is 2 PM in London. The result: insomnia at night, overwhelming fatigue during the day, difficulty concentrating, and disrupted digestion.

How long does jet lag last?

Without intervention, most people experience one day of jet lag symptoms for every time zone crossed. A 5-hour time zone shift? Expect 3-5 days of disrupted sleep, brain fog, and fatigue.

Eastward travel is harder than westward. Flying east (e.g. London to Tokyo) requires you to advance your body clock, going to sleep and waking up earlier than feels natural. Most people find this significantly harder than delaying their rhythm when flying west.

The good news: with the right strategy, you can dramatically cut recovery time. Studies show that proactive pre-flight adjustment, shifting your sleep and light exposure in the days before departure, can reduce jet lag recovery time by up to 50%.

The three tools: light exposure, caffeine timing, and sleep shifting

Your circadian rhythm responds to three primary signals. Knowing how to use each one is the foundation of any effective jet lag strategy.

Light exposure

Light is the most powerful signal for your body clock. When light hits your retina, it sends a direct message to the suprachiasmatic nucleus (your brain's master clock), telling it whether it's day or night.

Crucially, light at the wrong time can shift your clock in the wrong direction, making jet lag worse, not better. This is why getting bright light as soon as you land is sometimes exactly the wrong advice, depending on which direction you travelled.

• Even on cloudy days, outdoor natural light is bright enough to shift your clock.
• Even brief exposures of 15 to 30 minutes during sensitive windows have a meaningful effect.
• Screens and indoor lighting can also affect your clock, particularly in the hours before bed.
• For long-haul flights crossing 8 or more time zones east, morning light at your destination can backfire and push your clock the wrong way. Time light exposure to your biological clock, not the destination clock.

Caffeine timing

Caffeine works by blocking adenosine, the chemical that builds up throughout the day to make you feel sleepy. Used strategically, it can help you push through a stretch of alertness when your body clock would otherwise be winding down.

But here's what most people miss: caffeine has a half-life of around 5 to 6 hours. A 200 mg coffee at 2 PM still leaves roughly 100 mg active by 7 PM (about the caffeine in a strong cup of black tea) and 50 mg by midnight (roughly a cup of green tea), enough to impair sleep quality even if you feel fine.

Sleep schedule shifting

Gradually shifting your bedtime and wake time before your flight is one of the most effective jet lag prevention strategies. Moving your sleep window by just 30-60 minutes per day in the days leading up to departure can significantly ease the transition.

Travelling east? Start going to bed earlier and waking earlier. Travelling west? Delay your schedule. Even two or three days of pre-adjustment can make a noticeable difference.

Steps before your flight to prevent jet lag

The most effective window to start your jet lag plan is 3 to 5 days before departure. The goal is to gradually shift your body clock toward the destination's time zone before you even leave home.

A typical pre-flight plan for an eastward trip might look like this:

1. Day 1 (4 days out): Move bedtime 30 minutes earlier. Get morning light exposure.
2. Day 2 (3 days out): Another 30 minutes earlier. Avoid bright light in the evenings.
3. Day 3 (2 days out): Shift your caffeine cutoff earlier. Keep caffeine 8 hours before your new bedtime. If bedtime moves from 10 PM to 9 PM, stop caffeine by 1 PM.
4. Day 4 (1 day out): Maintain the shifted schedule. Avoid alcohol, which fragments sleep and delays adaptation.

Sleep strategies during the flight

Once on board, the goal is to behave as if you are already in your destination's time zone. If it is nighttime at your destination, sleep, even if it is daytime where you departed.

• Set your watch to the destination time zone immediately after boarding.
• Use an eye mask and earplugs to maximise your sleep quality if it is night at your destination.
• Avoid alcohol. It helps you fall asleep faster but significantly reduces sleep quality and delays circadian adaptation.
• Stay hydrated. Cabin air is extremely dry and dehydration amplifies fatigue.

Recovering after landing: adjusting to local time

The first day at your destination is critical. Resist the urge to nap for long stretches during the day, even if you are exhausted. A short nap (20-30 minutes) is fine, but sleeping for 2+ hours during the day will anchor your clock to home time.

Get outside. Natural daylight is your most powerful tool for resetting your clock once you have arrived. Aim for at least 30 minutes of outdoor light exposure.

How Armchair Jetlag creates your personalised jet lag plan

That is what Armchair Jetlag does. Enter your flight details and you get a day-by-day plan telling you exactly when to seek light, when to avoid it, when to stop caffeine, and when to shift your sleep window.