Jet Lag and Night Shifts: Working With Your Body Clock Instead of Against It
Your body runs on an internal clock in the hypothalamus, roughly 24 hours long, synchronised each day mainly by light reaching the eyes. Jet lag and shift work are the same problem: your internal clock and your external schedule disagree.
Why direction matters
The internal clock runs slightly longer than 24 hours in most people, which makes it easier to delay than to advance.
Travelling west means your day gets longer. You need to delay your clock, which is the easier direction. Adaptation is roughly one time zone a day, often faster.
Travelling east means your day gets shorter. You need to advance your clock, which is harder. Adaptation is roughly one time zone every one to one and a half days.
This is why flying from Europe to America is easier than the reverse, and it is the single most useful thing to know when planning.
North-south travel across few time zones causes travel fatigue but not true jet lag.
Light is the lever, and timing flips its effect
Light exposure shifts the clock, but the direction depends on when you get it relative to your body’s own low point, which is roughly two hours before your usual wake time.
- Light after your body’s low point advances the clock, making you sleep and wake earlier
- Light before your body’s low point delays the clock, making you sleep and wake later
Getting this backwards actively worsens jet lag, which is why wandering outside at the wrong time on arrival can make things worse rather than better.
Travelling east, to advance:
- Seek bright light in the destination morning
- Avoid light in the destination evening, including screens; sunglasses outdoors in the early evening help
- Shift bedtime earlier by an hour a day for two to three days before departure if possible
Travelling west, to delay:
- Seek bright light in the destination late afternoon and early evening
- Avoid bright morning light initially
- Shift bedtime later by an hour a day for a couple of days before departure
A practical rule of thumb for large eastward shifts of more than about eight zones: the body sometimes adapts more easily by delaying the long way round, so morning light avoidance for the first day or two can help. This is where a dedicated jet lag app that calculates timing for your specific itinerary genuinely earns its place.
Melatonin, used correctly
Melatonin is a timing signal, not a sleeping pill. Dose is less important than timing, and low doses of 0.5 to 3 mg are generally as effective as higher ones with fewer next-day effects.
- Travelling east: take it in the early evening at the destination, several hours before the target bedtime, to advance the clock
- Travelling west: it is less useful; light timing matters more. It may help with mid-night waking
Keep reading
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Taken at the wrong time it shifts the clock in the wrong direction. Check interactions, particularly with anticoagulants, and avoid it in pregnancy without advice.
Practical measures on the day
- Set your watch to destination time when you board and start thinking in that time
- Sleep on the plane only if it is night at your destination
- Stay hydrated; cabin air is very dry
- Limit alcohol, which fragments sleep and dehydrates
- Caffeine is useful for alertness but should stop at least six hours before your target sleep time
- Move around the cabin for circulation
- Eat according to destination mealtimes where you can, since meal timing is a secondary time cue
- On arrival, get outside at the correct time rather than napping all afternoon
- If you must nap, keep it to 20 to 30 minutes and before mid-afternoon
- For trips of two days or less, consider staying on home time rather than attempting to adapt twice
Shift work
Rotating and night shifts put you permanently out of phase, and the health consequences are well documented: increased risk of cardiovascular disease, metabolic syndrome and type 2 diabetes, gastrointestinal problems, mood disorders, and accidents from sleepiness.
Some of this is unavoidable in jobs that must be covered. A great deal can be reduced.
During the night shift:
- Bright light in the workplace during the first part of the shift improves alertness and helps shift the clock
- Dim the light toward the end of the shift
- Caffeine early in the shift, not in the last few hours
- A short nap before the shift, or a 20-minute nap during a break if permitted, measurably improves performance
- Eat a light meal rather than a heavy one at night; digestion is impaired overnight
Travelling home:
- Wear dark sunglasses on the journey home. Morning light tells your brain it is time to be awake, which is precisely what you do not want
- Drowsy driving after a night shift is a serious and underestimated risk; consider public transport, a lift, or a nap before driving
Sleeping during the day:
- Blackout curtains, eye mask, earplugs or white noise
- Phone on silent, and tell the household the rules
- Keep the room cool
- Aim for a consistent sleep period rather than scattered fragments
- Protect a seven to eight hour block
Shift scheduling, where there is any influence:
- Forward rotation, morning to evening to night, is easier than backward rotation
- Avoid quick turnarounds with under 11 hours between shifts
- Limit consecutive night shifts, typically to three or four
- Allow adequate recovery after a run of nights
On days off: full reversion to day schedule after a short run of nights is reasonable; after a long run it may be better to keep a partially shifted schedule rather than flip twice.
When to seek help
- Persistent insomnia despite good sleep practice
- Excessive sleepiness that affects safety, particularly driving
- Falling asleep involuntarily during the day
- Loud snoring with pauses, which suggests sleep apnoea and is worsened by shift work
- Low mood or anxiety that has developed alongside shift work
- Reliance on sleeping tablets or alcohol to sleep
Shift work sleep disorder is a recognised diagnosis with specific treatments, including prescribed wake-promoting agents in some cases.
The short version
Light is the control, and its timing decides whether it helps or harms: morning light to shift earlier, evening light to shift later. Travelling east is harder than west, melatonin is a timing signal rather than a sedative, and the highest-value habit for night workers is wearing dark glasses on the way home so the morning sun does not undo the day’s sleep before it starts.