Jet Lag

The term "jet lag" is used to describe the symptoms that result from a difference between the internal clock and the external environment when a traveller crosses several time zones rapidly. Physiologic rhythms that are innately synchronized with the day-night cycle have to be reset to match the new time zone. Although incompletely understood, these rhythms include diurnal variation in body temperature and cortisol secretion. The major known mediator of the internal clock is melatonin, which is secreted by the pineal gland and induces sleepiness. Daylight suppresses melatonin secretion; meals and other factors also influence secretion.

Symptoms of jet lag are temporary and include excessive daytime sleepiness, nighttime insomnia, decreased performance, headache, general malaise, and gastrointestinal symptoms. Individual responses to crossing time zones and ability to adapt to the new time zone vary. Increasing age, crossing more time zones, or travelling eastward generally increase the time required for adaptation. Eastward travel is associated with difficulty in falling asleep at the new bedtime and difficulty arising in the morning, while westward travel is associated with early evening sleepiness and predawn awakening.

A variety of nonpharmacologic therapies have been used to attenuate the symptoms of jet lag. In principle, efforts to adjust light exposure, activity, and meal times to the new schedule as soon as possible after arrival promote more rapid resetting of the internal clock. Outside daylight, even on cloudy days, is more intense than interior lighting. Light masks and light boxes are available for purchase and at some hotels. Persons travelling eastward should seek bright light in the morning, while those travelling westward should seek bright light in the afternoon. In general, the more time spent outdoors in the first several days following travel, the faster the adjustment to the new time zone. The Argonne diet, which alternates high- and low-calorie days before departure, is often cited but has not been formally studied. The main benefit of this diet may be the inclusion of high-protein breakfasts, which increase levels of tyrosine and thus epinephrine and dopamine, promoting alertness, and high-carbohydrate dinners, which increase serotonin and melatonin, promoting evening sleepiness.

Over-the-counter and prescription medications have been used to promote sleep on long trips or at the new bedtime after arrival. Melatonin is available in the United States as an herbal supplement, although it is regulated in Canada and prohibited in some European countries. Since it is not under FDA regulation, rigorous studies of safety or standardization of doses are not available. However, melatonin seems to be safe and well tolerated, and doses of 0.5-5 mg promoted sleep and decreased jet lag in travellers crossing five or more time zones. Five-mg doses promoted more rapid sleep than lower doses; doses >5 mg had no additional benefit. Slow-release forms were not effective. Melatonin should be taken at the target bedtime, beginning 3-4 days before departure if possible. Zolpidem, a prescription nonaddictive sedative, has been shown to promote sleep in a small group of travellers; its effect on the internal clock is not known. Benzodiazepines may have a direct effect on neurons mediating the internal clock, as well as a hypnotic effect. Short-acting drugs in this class, such as temazepam, should be used to minimize oversedation the next day.

Agents that promote alertness, such as caffeine, and prescription medications, such as amphetamines and pemoline, may interfere with normal sleep and often have adverse effects and potential for dependence. One small study suggests that NADH (nicotinamide adenine dinucleotide), available as a nutritional supplement, may improve performance on the first post-arrival day; more data regarding its efficacy and safety are needed.

• Reid KJ, Chang AM, Zee PC. Circadian rhythm sleep disorders. Med Clin North Am. 2004;88:631-51.
• Herxheimer A. Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev. 2002;4:463-6.
• Jamieson AO, Zammit GK, Rosenberg RS, et al. Zolpidem reduces the sleep disturbance of jet lag. Sleep Med. 2001;2:423-30.
• Virre ES, Kay GG. Assessing the efficacy of pharmaceuticals and nutraceuticals as countermeasures for jet lag. Proceedings of the 7th Conference of the International Society of Travel Medicine; 2001 May 27-31; Innsbruck, Austria.

- Tamara Fisk

Medic8® Health Information for International Travel