Chronobiology & Circadian Rhythms ★★☆ Moderate

✈️ Jet Lag — Circadian Disruption & Recovery

Model circadian clock desynchrony after long-haul flights. Adjust time zones crossed, direction of travel, and light-exposure strategy to minimise recovery days using a two-oscillator phase model.

Phase gap: 0.0 h Recovery: 0 days Advance rate: 1.0 h/day Direction: — Day: 0
5 tz
0.40
OFF

How to read the chart

Blue sine = body clock (internal circadian oscillator, ~24.2 h period). Orange sine = local light zeitgeber (environmental 24 h signal). The shaded region shows the phase gap (desynchrony). As the body clock re-entrains, the gap closes. Green band = sleep window (22:00–06:00 local). Melatonin boost (slider > 0) adds ~1.5 h/day to the advance rate, mimicking exogenous melatonin 5 h before target sleep.

The Physics

Phase shift dφ/dt = ω₀ + K·sin(φ_light − φ_clock), where K is coupling strength and ω₀ is intrinsic period (~24.2 h). Eastward travel requires phase advance (harder); westward requires phase delay. Melatonin administered 5h before target sleep accelerates re-entrainment by ~1.5 h/day. Recovery days ≈ |Δtz| / advance_rate.

About Jet Lag Simulator

Jet lag is a temporary circadian rhythm disorder caused by rapid travel across multiple time zones, misaligning the body's internal biological clock with local environmental time cues. The circadian clock — a roughly 24-hour oscillation generated by feedback loops of clock genes (CLOCK, BMAL1, PER, CRY) in the suprachiasmatic nucleus (SCN) of the hypothalamus — governs sleep-wake cycles, hormone secretion, body temperature, and metabolism.

When crossing time zones, external cues (light-dark cycles, meal times, social interactions) shift immediately to local time, but the internal clock adapts gradually at approximately 1–2 hours per day. Eastward travel is generally harder than westward because it requires phase advances (going to bed earlier), which the circadian clock accommodates more slowly than phase delays. Symptoms include daytime sleepiness, difficulty sleeping at night, impaired concentration, gastrointestinal disturbances, and malaise.

Recovery strategies are modelled mathematically using the Van der Pol oscillator or two-process model of sleep regulation. Practical interventions include strategic light exposure (the most powerful zeitgeber or time-cue), melatonin supplementation to accelerate clock shifting, timing of meals and exercise, and sleep scheduling. Algorithms such as Timeshifter (co-developed by circadian biologists) generate personalised protocols based on the destination, flight times, and individual chronotype.

Frequently Asked Questions

Why does jet lag feel worse when flying east than west?

The human circadian clock has a natural period slightly longer than 24 hours (around 24.2 h), meaning it more naturally delays (runs late) than advances. Westward travel aligns with this tendency (phase delays), while eastward travel requires phase advances against the clock's natural drift, making adaptation slower and symptoms more severe.

What is melatonin and how does it help with jet lag?

Melatonin is a hormone secreted by the pineal gland in darkness that signals the body to prepare for sleep. Taking low-dose melatonin (0.5–3 mg) at the target destination's bedtime helps shift the circadian clock toward the new time zone. Timing is critical — taken at the wrong time, melatonin can shift the clock in the wrong direction and worsen jet lag.

Why is light exposure the most effective jet lag treatment?

Light is the primary zeitgeber (time-giver) that entrains the circadian clock. The SCN contains intrinsically photosensitive retinal ganglion cells (ipRGCs) containing melanopsin, which relay bright light signals directly. Appropriately timed bright light — especially blue-enriched morning light in the new time zone — powerfully advances or delays the clock, accelerating re-entrainment by 1–2 extra hours per day compared to natural adaptation.

How do airlines and pilots manage chronic jet lag?

Frequent travellers and aircrew face chronic circadian disruption that impairs health, cognitive performance, and mood. Airlines follow regulatory fatigue risk management systems (FRMS) based on biomathematical models. Pilots use pre-flight sleep banking, light avoidance goggles, and strategic napping. Flight crew unions and aviation regulators continue to update duty time limitations based on circadian biology research.

Can jet lag be predicted and simulated mathematically?

Yes. The Hannay–Forger–Booth model and the Jewett–Kronauer model mathematically simulate circadian phase using coupled oscillators responding to light input. These models predict internal circadian phase shift over time following any travel itinerary and light-exposure schedule. Apps like Timeshifter implement these models to generate personalised jet lag minimisation protocols.

About this simulation

This simulator models jet lag as two coupled phase oscillators — your body clock, period near 24.2 hours, and the local light zeitgeber, locked to a 24-hour day. The gap between them, dφ/dt = ω₀ + K·sin(φlight − φclock), closes over days as K pulls the clock into step, with optional melatonin as an extra nudge.

🔬 What it shows

An indigo body-clock curve and an orange light curve, both sine waves plotted against days since departure. The shaded region between them is the phase gap in hours; a green band marks the 22:00–06:00 sleep window, and live stats report the gap, estimated recovery days, and advance rate.

🎮 How to use

Set Time zones crossed (1–15) and pick Direction — Westward (delay) or Eastward (advance). Coupling strength K (0.1–1.0) sets re-entrainment speed, and Melatonin boost (0–1) adds up to 1.5 extra hours/day. Try the London→New York, London→Tokyo, New York→Sydney or Short Haul presets, or Pause/Reset.

💡 Did you know?

Because the circadian clock naturally runs about 12 minutes longer than 24 hours, it delays more easily than it advances — the real reason eastbound flights (like London to Tokyo) usually cause worse jet lag than westbound ones of the same size.

Frequently asked questions

Why does the Direction setting change recovery so much?

Westward travel needs a phase delay, given a base rate of about 1.5 hours/day matching the clock's natural drift. Eastward needs a phase advance against that drift, modelled at only about 1.0 hour/day — roughly a third slower, matching real jet lag studies.

What exactly does Coupling strength K control?

K scales the sin(φ_light − φ_clock) term — how strongly light pulls the body clock toward local time. Higher K gives faster, more forceful re-entrainment; low K lets the clock drift near its own 24.2-hour pace.

How does the Melatonin boost slider work?

Sliding it above OFF adds up to 1.5 hours/day to the advance rate, roughly modelling melatonin taken near target bedtime. The bonus applies more fully eastward than westward, reflecting how melatonin mainly helps the harder advance direction.

Why do the presets use such different tz and K values?

London→New York (5 tz, K 0.4, westward) is a comparatively easy delay. London→Tokyo (9 tz, K 0.35, eastward, melatonin on) needs more help. New York→Sydney (15 tz, K 0.3, eastward, high melatonin) is the most extreme case, needing the longest recovery.

How is the Recovery day count actually calculated?

The simulator divides time zones crossed by the current advance rate: recovery days ≈ |Δtz| / advance rate. Since that rate depends on direction and melatonin, identical time-zone counts can need very different numbers of days.