• jet lag syndrome emerged with the rise of long haul air travel - symptoms include disturbed sleep, loss of concentration, increased fatigue, and increased irritability during the new daytime, and yet difficulties in initiating and maintaining sleep at night
  
  
• long flights are also often uncomfortable and tiring (travel fatigue), and the dry cabin air contributes to dehydration
  • travel fatigue can be distinguished from those of jet lag by comparing flights across time zones, for example from Europe to Asia, with flights of similar length along the same meridian, say to southern Africa, which cause travel fatigue but no jet lag (1)
    
    
• jet lag is caused by the desynchronisation between various body rhythms and environmental rhythms
  • symptoms are usually temporary and resolves when the endogenous circadian rhythm resynchronizes with the physical environment
  • severity of the symptoms may vary according to the number of time zones crossed and the direction of travel e.g. - people who take eastward flights have more sleep disturbances than people who travel towards the west (2)
  • the cycle of sleep and activity is the rhythm most noticeably affected, with the associated changes in physical and mental functioning - rhythms are regulated by the interaction between internal and external factors:
  • an example of interaction between internal and external factors:
    • "body clock" which controls secretion of melatonin by the pineal gland, an important internal factor, and light
      • melatonin is synthesized at night under normal environmental conditions
        • the endogenous rhythm of secretion is generated by the suprachiasmatic nuclei and entrained by the light/dark cycle
        • light is able to both suppress or synchronize melatonin production according to the light schedule
        • melatonin can be considered as the output (the hand) of the endogenous clock
        • exogenous melatonin is able to influence the endogenous secretion of the hormone according to a phase response curve
  • with a rapid change of time zone, it takes several days for the external factors to shift the phase of the body clock from the time zone just left to the new zone - if this adaptive shift is speeded up then jet lag can be alleviated or prevented
    

Treatment:

• non-drug measures in management of jet lag
  • these aim to maximise the external environmental cues that push the circadian phase towards the rhythm of light and dark at the destination - these changes may be worth trying to start this before departure
  • the most important cue is light
    • regardless of the course of travel, people should try to stay awake during the daytime at the destination (2)
    • after a westward flight - changes in behaviour would be to stay awake while it is daylight at the destination and to try to sleep when it gets dark
    • after an eastward flight - changes in behaviour would be to be awake but avoid bright light in the morning, and to be outdoors as much as possible in the afternoon
    • these changes in behaviour will lead to an adjustment in the body clock and turn on the body's own melatonin secretion at the right time
  • other cues can reinforce this change in the body clock e.g. eating modestly at the times that correspond to one's usual mealtimes, taking comfortable exercise, and seeing favourite sights at times when bright light is advised (1)
  • it is unclear whether alcohol or caffeine affect adaptation although it seems more likely that they hinder rather than to help adaptation (1)
  • when the stay at the destination is short (i.e., two days or less) travellers may be advised to keep a home-based sleep hours rather than adopting to the destination sleep hours to minimise sleepiness and jet lag symptoms (3)
    
    
• melatonin and drug measures e.g. a short acting hypnotic
  • melatonin taken at bedtime both shifts the phase and has a hypnotic effect
  • a hypnotic treats one symptom by providing sleep- however does not shift the circadian phase
  • adverse effects with melatonin have been reported rarely but have not been looked for systematically. Reports of adverse events possibly related to use of melatonin imply that two categories of people should avoid it until more is known: anyone taking warfarin or another oral anticoagulant, and people with epilepsy (2)
    • a Cochrane review concluded (2) that 2-5 mg melatonin taken at bedtime after arrival is effective and may be worth repeating for the next two to four days, together with the non-drug measures already mentioned - however people who have not had jet lag on a previous trip may well never need it
    • however a more recent review (4) came to different conclusion and stated that there was "no evidence that melatonin is effective in treating secondary sleep disorders or sleep disorders accompanying sleep restriction, such as jet lag and shiftwork disorder. There is evidence that melatonin is safe with short term use"
  • melatonin is a simple substance, but no official standards of purity exist (1) It's effect on daytime symptoms of jet lag have not been well establiblished (7)
  • patients should be warned about alcohol intake and the risk of interaction with hypnotics (7)

Reference

• 1. BMJ 2003 Feb 8;326(7384):296-7
• 2. Barion A, Zee PC. A clinical approach to circardian rhythm sleep disorders. Sleep Med. 2007;8(6):566-577
• 3. Morgenthaler TI et al. Practice Parameters for the Clinical Evaluation and Treatment of Circadian Rhythm Sleep Disorders - An American Academy of Sleep Medicine Report. Sleep. 2007;30(11):1445-1459
• 4. Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Library 2002; disk issue 4:CD001520.
• 5. Restor Neurol Neurosci 1998;12(2,3):151-157
• 6. Buscemi N et al. Efficacy and safety of exogenous melatonin for secondary sleep disorders and sleep disorders accompanying sleep restriction: meta-analysis. BMJ. 2006 Feb 18;332(7538):385-93
• 7. Sack RL et al. Circadian Rhythm Sleep Disorders: Part I, Basic Principles, Shift Work and Jet Lag Disorders - An American Academy of Sleep Medicine Review. Sleep 2007;30(11)