Does travel-related circadian misalignment disrupt cortisol, melatonin, core body temperature, and sleep continuity?

Travel-related circadian misalignment, commonly experienced as jet lag, occurs when rapid transit across time zones desynchronizes the central circadian pacemaker from local environmental cues. This mismatch profoundly disrupts the coordinated physiological rhythms that govern the sleep-wake cycle.

Endocrine and thermal disruption

• Melatonin suppression: Misalignment causes severe phase shifts in dim-light melatonin onset (DLMO) and reduces nocturnal melatonin secretion amplitude by up to 50%.
• Cortisol dysregulation: The diurnal cortisol rhythm—normally characterized by a morning peak and nocturnal trough—becomes flattened, distorted, or completely inverted.
• Core body temperature (CBT) shifts: The 24-hour CBT rhythm becomes decoupled from the target bedtime, delaying the temperature minimum (nadir) and flattening the overall temperature curve.

Mechanistic drivers of sleep fragmentation

• Loss of sleep-promoting cues: When melatonin levels remain low and CBT remains elevated during attempted local sleep, the body fails to initiate and consolidate sleep.
• Inappropriate wake promotion: Inappropriately timed, elevated cortisol levels near the desired bedtime promote alertness and fragment sleep.
• Sleep architecture degradation: This internal desynchrony leads to a substantial ~20% reduction in sleep efficiency, characterized by increased wake after sleep onset (WASO) and a reduction in restorative slow-wave and REM sleep.

Bottom line

• Travel-induced circadian misalignment directly disrupts the synchronized rhythms of cortisol, melatonin, and core body temperature. This multi-system desynchrony is the primary driver of sleep fragmentation, reducing overall sleep efficiency by approximately 20% and impairing sleep continuity.