Light exposure is the strongest external signal for shifting your body clock.
Travel intelligence / Essential guide
Jet lag,
understood properly.
A practical guide to the timing signals that help your body adapt across time zones, with clear distinctions between circadian adjustment and general travel recovery.
The essentials
What matters most.
The correct timing depends on travel direction and your current circadian phase.
Starting one to three days before departure can make the transition easier.
Sleep, meals and caffeine support the plan, but they do not replace timed light.
01 / The condition
What is jet lag?
Jet lag, medically known as desynchronosis, occurs when rapid travel leaves your internal circadian rhythm out of step with local time. Your body is still responding to the light and dark cycle of your origin while your destination is operating to a different schedule.
Common effects include daytime fatigue, difficulty sleeping at local night-time, reduced concentration, changes in appetite and digestive disruption. General travel fatigue may improve after rest, but circadian misalignment resolves as the body clock gradually adjusts to local timing cues.
02 / The primary signal
The role of light.
Light is the strongest environmental cue for the circadian system. Exposure at the correct time can move the body clock in the required direction. Exposure at the wrong time can work against the adjustment you are trying to make.
03 / Before departure
Strategic pre-adjustment.
For larger time-zone changes, begin shifting sleep and wake times one to three days before departure. Even a partial adjustment can reduce the difference your body has to absorb after arrival.
Move earlier.
Bring bedtime, wake time and morning light forward gradually where your normal routine allows.
Move later.
Delay bedtime, wake time and useful light exposure gradually rather than forcing an abrupt change.
04 / Additional support
The role of melatonin.
Melatonin is a hormone associated with biological night. In some circumstances, carefully timed supplementation may support sleep timing and circadian adjustment. Taking it at an unsuitable time can be counterproductive, and availability varies by country.
05 / In transit
Use the journey deliberately.
The goal is not to follow every instruction perfectly. It is to make the highest-value timing decisions consistently enough to support the destination schedule.
01
Move onto destination time
Use destination time for sleep, meals and key decisions as early as is practical during the journey.
02
Use caffeine deliberately
Use it when destination-time alertness is useful, then stop early enough to protect the planned sleep window.
03
Treat hydration as travel support
Regular water intake can reduce travel fatigue and headaches, even though hydration itself does not reset the body clock.
Turn guidance into timing
Build a plan around your route and travel times.
Get a personalised schedule for light, sleep, meals and caffeine before departure and through your first days at the destination.