CLINICAL REVIEWManaging jet lag: Some of the problems and possible new solutions
Introduction
In the last few years at least 15 reviews have addressed this subject or the broader subject of circadian rhythm sleep disorders.1, 2, 3, 4, *5, 6, 7, 8, 9, *10, 11, *12, 13, 14, *15 Rather than repeating this exercise the present review, after an introduction and summary, will consider problems of effective treatment and potential future means of managing jet lag.
Jet lag has never been completely defined, although anyone who has suffered from this problem has no difficulty in identifying their personal symptoms. It is formally described as circadian desynchrony, or a mismatch between the timing of the internal circadian (circa 24 h) clock(s) and the external environment. After an abrupt shift in time cues such as after time zone change the circadian system adapts slowly to realign with the new schedule, approximately one day for each hour of time zone change, faster westwards, with different components of the system adapting at different rates (internal desynchrony).5
The perceived manifestations are variable from one individual to another, with number of time zones crossed, with direction and timing of flights and probably with seasons. However, the major complaints are poor sleep, daytime fatigue and poor performance.*15, 16 Travelling eastwards, short sleep and long sleep latency are common, travelling westward short sleep and early wake up are manifest. Poor alertness and fatigue during daytime are attributed partly to sleep deprivation and partly to the concomitant presence of night time rhythm physiology – the nadir of the core body temperature, alertness, performance, metabolism and the peak of melatonin secretion. In this Olympic year of 2008 with many athletes travelling over large numbers of time zones to Beijing, the question of physical performance has been addressed in some detail.3, *5, 8 One of the earliest descriptions of the effects of jet lag on physical performance concerned American baseball players who performed significantly worse when playing away over an eastward time zone transition.17
There are possible long term consequences of frequent desynchrony as evidenced by epidemiological and animal studies.18, 19, 20, *21 These include cognitive deficits, gastrointestinal problems, increased risk of cancer, infertility and heart disease. However, not all reports are consistent. Adapting to phase shift becomes harder as we grow older for uncertain reasons.22, 23
Section snippets
Circadian timing system
We are a diurnal species: human physiology and behaviour are normally aligned with the 24 h day such that we are alert and active during the daylight hours and asleep during the dark phase of the day. Evidently social and work constraints can impose other behavioural arrangements: shift work is the primary example and many of the problems of jet lag are common to shift work. However, for most people jet lag symptoms resolve in time as the circadian system adapts to the new time cues, whereas
Resetting human circadian rhythms
Because human tau is not exactly 24 h the circadian system has to be reset daily or at least frequently in order to maintain 24 h clock time. For a tau of, e.g., 24.5 h the timing must be advanced by 0.5 h per day and for a tau of 23.5 h it must be delayed by 0.5 h per day. The factors which synchronise/entrain or reset the clock are known as zeitgebers (time-givers or time cues). The most important by far is the alternation of light and darkness. Blind people with no perception of light frequently
Individual variability when adapting to phase shift/time zone change
The faster the circadian system adapts to the new time zone the shorter the symptomatic period. Thus hastening adaptation is a primary goal. If it were possible to predict the precise times of exposure to specific zeitgebers such as light and/or melatonin for an individual subject and journey, and if compliance were complete, we should be close to resolving the problem. The use of all available time cues theoretically will have the greatest efficacy. Light exposure during biological night will
Current strategies to manage jet lag
Whether to aid adaptation or not depends on the length of time to be spent in the destination time zone. For short stop-overs (e.g., business trips for a day or 2) there is little point in provoking adaptation as subjects will not be completely adapted whatever the approach and will be at least partly out of synchrony when returning home. Advice is to obtain sleep and alertness by whatever means and to schedule important meetings at times of maximum alertness in the departure time zone. Naps,
Potential new treatments
Endogenous melatonin is thought to facilitate and reinforce sleep and other aspects of night-time physiology, when it is appropriately timed. Exogenous melatonin provides a biological signal for dawn and dusk, to change the timing of the ‘internal clock’, and promotes sleepiness or sleep during biological day.86 In most countries its availability is restricted and only recently, for example, has one particular formulation (Circadin) been approved for prescription use in Europe (//www.emea.europa.eu/humandocs/Humans/EPAR/circadin/circadin.htm
Use and avoidance of short wavelength light
Since light exposure and avoidance of such are the main environmental factors governing adaptation to time zone change, it is of considerable importance that the spectral quality of light strongly influences the circadian response. In the absence of rods and cones, i.e., normal vision, the circadian system can nevertheless respond to light. This observation, made originally in rodless, coneless mice89 has led to the discovery of a novel circadian photoreception pathway which employs light
Predicting tolerance to jet lag (and shift work)
Possibly the most important discovery in recent years regarding the problems of circadian desynchrony relates these problems to a polymorphism in the clock gene PER3. In 2000 Archer et al,35 reported that a variable-number tandem-repeat polymorphism in the coding region of the circadian clock gene PERIOD3 (PER3, 5/5, 4/5, 5/5) associated with diurnal preference and delayed sleep phase syndrome, with the long variant (5/5) being associated with extreme morningness and the short variant (4/4)
Conclusions
Jet lag is a problem for most time zone travellers, affecting sleep, performance and with possible long-term health consequences. It is due to the misalignment of the internal circadian clock(s) with external time cues. For short stopovers (1–2 days) it is advisable not to try and adapt but to schedule critical activities to daytime in the departure time zone and maintain alertness and sleep by short-term measures such as judicious naps, caffeine and short acting hypnotics. For intermediate
Acknowledgements
This review was written during the tenure of an unrestricted research grant from Philips Lighting, and with support from Stockgrand Ltd., University of Surrey. I am particularly grateful to Dr. Benita Middleton for her collaboration and support.
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2023, Applied ErgonomicsCitation Excerpt :One key problem faced by long-haul aircrew is jet lag, a condition associated with disrupted sleep, fatigue, daytime sleepiness, impaired mood, gastro-intestinal function and cognitive performance (Atkinson, 2013). The main cause of jet lag symptoms is circadian desynchrony, a mismatch between the internal timing of the circadian clock, e.g. melatonin peak time, and the light/dark cycle in the new time zone following transmeridian travel (Arendt et al., 2000, 2009; Waterhouse et al., 2007). As well as external desynchrony, internal rhythms have also been shown to uncouple, for example when the individual's sleep/wake cycle is out of phase with the melatonin rhythm (Roach et al., 2002).
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