The body clock adjusts at roughly one hour per day when moving westward, meaning a Tokyo to Paris arrival (8-hour difference westbound) typically takes around eight days for full circadian realignment. Sleep researcher Charles Czeisler at Harvard Medical School has shown that bright light exposure in the destination morning hours (typically between early morning and mid-morning local) advances the body clock substantially faster than the natural drift rate.
Light Exposure and Melatonin Timing
Light boxes outputting 10,000 lux at close range for around 30 minutes mimic daylight exposure in dim winter conditions in northern Europe. Apps including Timeshifter and Entrain calculate personalised light schedules from departure and arrival timestamps. Melatonin at 0.5-1 mg taken roughly 30 minutes before destination bedtime accelerates the phase shift; higher doses in the 3-5 mg range can paradoxically harm sleep architecture per recent meta-analyses in Sleep Medicine Reviews.
Pre-Flight Adjustment Strategies
Westbound travellers benefit from delaying bedtime by one hour for two nights pre-departure on a Tokyo-London routing, easing the morning arrival into the lighter London morning. Caffeine intake should be confined to before noon local destination time on the arrival day. Alcohol and large meals impair the adjustment by suppressing REM sleep and irregularising melatonin secretion.
Arrival Day Recovery Protocol
Arrival in London from a Tokyo overnight rotation calls for around 20-minute outdoor exposure within the first 90 minutes, a light high-protein breakfast and avoidance of caffeine after early afternoon. A short nap before mid-afternoon recovers sleep debt without compromising the evening sleep window. Exercise at low intensity for around 30 minutes on arrival day advances core body temperature decline, supporting the new sleep timing. Full alignment typically clears by the fifth day for an 8-hour westbound shift.