Reentrainment of the circadian pacemaker during jet lag: East-west asymmetry and the effects of north-south travel

Oct 9, 2017Journal of theoretical biology

Resetting the body clock after jet lag: Differences between east-west and north-south travel

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Abstract

Reentrainment time for travel between any two points on the globe can be calculated using mathematical and computational analysis.

Jet lag symptoms, including sleep problems and indigestion, may arise from disruptions in circadian rhythms due to rapid travel across time zones.
The east-west asymmetry of jet lag severity is linked to the traveler's circadian clock period and the length of the day, rather than just the typical assumption about the 24-hour cycle.
The behavior of the entrainment map's unstable fixed point may influence whether reentrainment occurs through phase advances or phase delays.
North-south travel can induce jet lag due to changes in daylength, even when crossing no time zones.
Proposed techniques could help travelers minimize jet lag when visiting multiple destinations with varying time zones and latitudes.

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The normal alignment of circadian rhythms with the 24-h light-dark cycle is disrupted after rapid travel between home and destination time zones, leading to sleep problems, indigestion, and other symptoms collectively known as jet lag. Using mathematical and computational analysis, we study the process of reentrainment to the light-dark cycle of the destination time zone in a model of the human circadian pacemaker. We calculate the reentrainment time for travel between any two points on the globe at any time of the day and year. We construct one-dimensional entrainment maps to explain several properties of jet lag, such as why most people experience worse jet lag after traveling east than west. We show that this east-west asymmetry depends on the endogenous period of the traveler's circadian clock as well as daylength. Thus the critical factor is not simply whether the endogenous period is greater than or less than 24 h as is commonly assumed. We show that the unstable fixed point of an entrainment map determines whether a traveler reentrains through phase advances or phase delays, providing an understanding of the threshold that separates orthodromic and antidromic modes of reentrainment. Contrary to the conventional wisdom that jet lag only occurs after east-west travel across multiple time zones, we predict that the change in daylength encountered during north-south travel can cause jet lag even when no time zones are crossed. Our techniques could be used to provide advice to travelers on how to minimize jet lag on trips involving multiple destinations and a combination of transmeridian and translatitudinal travel.

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Reentrainment of the circadian pacemaker during jet lag: East-west asymmetry and the effects of north-south travel

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