CDC Yellow Book 2024Travel by Air, Land & Sea
Jet lag results from a mismatch between a person’s circadian (24-hour) rhythms and the time of day in the new time zone. When establishing risk of jet lag, first determine how many time zones a traveler will cross and what the discrepancy will be between time of day at home and at the destination at arrival. During the first few days after a flight to a new time zone, a person’s circadian rhythms are still anchored to the time of day at their initial departure location. Rhythms then adjust gradually to the new time zone.
A useful web-based tool for world time zone travel information is available. For travelers crossing ≤3 time zones, especially if they are on a long-haul flight, symptoms (e.g., tiredness) are likely due to fatigue rather than jet lag, and symptoms should abate 1–3 days post-flight.
Many people flying >3 time zones for a vacation accept the risk for jet lag as a transient and mild inconvenience, but people traveling on business or to compete in athletic events might desire advice on prophylactic measures and treatments. If a traveler spends ≤2 days in the new time zone, they might prefer to anchor their sleep–wake schedule to the time of day at home as much as possible. Consider recommending short-acting hypnotics or alertness-enhancing drugs (e.g., caffeine) for such travelers to minimize total burden of jet lag during short round trips.
Jet lag symptoms can be difficult to define because of variation among people and because the same person can experience different symptoms after each flight. Jet-lagged travelers typically experience ≥1 of the following symptoms after flying across >3 time zones: gastrointestinal disturbances, decreased interest in food or enjoyment of meals; negative feelings (e.g., anxiety, depression, fatigue, headache, inability to concentrate, irritability); poor performance of physical and mental tasks during the new daytime; and classically, poor sleep, including (but not limited to) difficulty initiating sleep at the usual time of night (after eastward flights), early awakening (after westward flights), and fractionated sleep (after flights in either direction).
Symptoms are difficult to distinguish from the general fatigue resulting from international travel itself, as well as from other travel factors (e.g., hypoxia in the aircraft cabin). Validated multi-symptom measurement tools (e.g., Liverpool Jet Lag Index) can help distinguish between jet lag and fatigue. When travelers cross only 1–2 time zones, though, symptoms of and treatment for jet lag are not readily distinguishable from those for general travel fatigue.
In addition to jet lag symptoms, crossing multiple time zones can affect the timing of regular medication used for chronic conditions and illnesses. This can particularly affect patients taking medications with short half-lives that require >1 dose each day. Consider the destination and traveling time when evaluating travelers who take long-term medications, and recommend strategies to keep them on their dosing schedule.
Prevention & Treatment
Travelers use many approaches—before, during, and after flying—to reduce jet lag symptoms. In one survey, 460 long-haul travelers indicated that seat selection and booking a direct flight were primary strategies to reduce jet lag. Nearly all study participants used ≥1 behavioral strategy during their flight, including consuming or avoiding alcohol and caffeine (81%), altering food intake (68%), using light exposure (53%), periodic walking down the aisle of the plane (35%), and taking medication (15%), including melatonin (8%). Only 1 respondent used a jet lag application on a mobile device. Fewer people used all these strategies before take-off and after arrival.
After arrival, light and social contacts influence the timing of internal circadian rhythms. A traveler staying in the time zone for >2 days should quickly try to adjust to the local sleep–wake schedule as much as possible.
Diet & Physical Activity
Most dietary interventions or functional foods have not been proven to reduce jet lag symptoms in randomized controlled trials and real flight conditions (see Sec. 2, Ch. 14, Complementary & Integrative Health Approaches to Travel Wellness). Most trials are in simulated flight conditions and have a high risk of bias, including studies looking at the effectiveness of Centella asiatica, elderberry, echinacea, pinokinase, and diets containing various levels of fiber, fluids, or macronutrients. In one study, long-haul flight crew who adopted more regular mealtimes showed a small improvement in their general subjective rating of jet lag, but not the separate symptoms of alertness or jet lag, on their days off work.
Because gastrointestinal disturbance is a common jet lag symptom, travelers might better tolerate smaller meals than larger ones before and during the flight; this strategy has not been investigated in a formal trial, however. Travelers might find caffeine and physical activity can help ameliorate daytime sleepiness at the destination, but little evidence exists to indicate that these interventions reduce overall feelings of jet lag. Any purported treatments based on use of acupressure, aromatherapy, or homeopathy have no scientific basis.
Prescription medications (e.g., temazepam, zolpidem, zopiclone) can reduce sleep loss during and after travel but do not necessarily help resynchronize circadian rhythms or improve overall jet lag symptoms. If indicated, prescribe the lowest effective dose of a short- to medium-acting compound for the initial few days of travel, bearing in mind these drugs do have adverse effects. In 2019, the US Food and Drug Administration (FDA) issued a warning about rare but serious adverse events (i.e., injuries caused by sleepwalking) occurring after patients took some sleep medications; adverse events were more commonly reported with eszopiclone, zaleplon, and zolpidem.
Caution travelers about taking hypnotics during a flight because the resulting immobility could increase the risk for deep vein thrombosis. Travelers should not use alcohol as a sleep aid, because it disrupts sleep and can provoke obstructive sleep apnea.
Exposure to bright light can advance or delay human circadian rhythms depending on when it is received in relation to a person’s body clock time. Consequently, some researchers have proposed schedules for good and bad times for light exposure after arrival in a new time zone.
The best circadian time for light exposure might be at a time that is dark after crossing multiple time zones, raising the question of whether a light box is helpful. One small randomized controlled trial on supplementary bright light for reducing jet lag did not find clinically relevant effects of supplementary light on jet lag symptoms after a flight across 5 time zones going west.
Melatonin & Melatonin-Receptor Analogs
Probably the most well-known treatment for jet lag, melatonin, is secreted at night by the pineal gland. Melatonin delays circadian rhythms when taken during the rising phase of body temperature (usually the morning) and advances rhythms when ingested during the falling phase of body temperature (usually the evening). These effects are opposite to those of bright light.
The instructions on most products advise travelers to take melatonin before nocturnal sleep in the new time zone, irrespective of the number of time zones crossed or direction of travel. Studies published in the mid-1980s indicated a substantial benefit of taking melatonin just before sleep to reduce overall feelings of jet lag after flights. Subsequent larger studies did not replicate these earlier findings, however, and more research on melatonin’s use in jet lag is needed.
Melatonin is a very popular sleep aid for jet lag in the United States, and no serious side effects have been linked to its use, although long-term studies have not been conducted. The American Academy of Sleep Medicine and the US National Center for Complementary and Integrative Health suggest that melatonin could be used to reduce symptoms of jet lag, although they caution that melatonin might not be safe when combined with some other medications. In addition, melatonin is considered a dietary supplement in the United States and is not regulated by the FDA. Therefore, the advertised concentration of melatonin has not been confirmed for most products on the market, and the presence of contaminants cannot be ruled out (see Sec. 2, Ch. 14, Complementary & Integrative Health Approaches to Travel Wellness).
A recent UK Drug and Therapeutics Bulletin stated that melatonin might increase the frequency of seizures in people with epilepsy. In addition, because it can potentially induce proinflammatory cytokine production, melatonin should not be taken by those with autoimmune diseases. Due to the potential for these problems, and the limited evidence from randomized controlled trials for any benefits, melatonin is not recommended in the United Kingdom.
Ramelteon, a melatonin-receptor agonist, is an FDA-approved treatment for insomnia. One milligram taken just before bedtime can decrease sleep onset latency after eastward travel across 5 time zones. Higher doses do not seem to lead to further improvements, and the effect of this medication on other symptoms of jet lag and the timing of circadian rhythms is unclear. In a well-designed multicenter trial involving simulated jet lag conditions, tasimelteon (a dual melatonin-receptor agonist) improved jet lag symptoms, including nighttime insomnia and daytime functioning; real-world evidence is needed to support or refute its use in the amelioration of jet lag.
Several mobile device applications (apps) can provide tailored advice to manage jet lag symptoms. Depending on how many time zones the traveler has passed through. Timeshifter provides advice on when to use caffeine, light, melatonin, and sleep. Another app offering tailored advice was tested for use over several months of frequent flying. Participants reported reduced fatigue compared with the comparator group and improved aspects of health-related behavior (e.g., physical activity, snacking, and sleep quality) but not other measures of sleep (e.g., duration, latency, use of sleep-related medication). Although this and other apps are based on information from published laboratory-based experiments, they lack randomized controlled trials on their effectiveness for reducing jet lag symptoms after actual long-haul flights.
Multiple therapies to decrease jet lag symptoms can be combined into treatment packages. Marginal gains from multiple treatments could aggregate. In one small trial, a treatment package involving light exposure and sleep hygiene advice improved sleep quality and physical performance after an eastward flight across 8 time zones. The American Sleep Association offers general sleep hygiene advice.
In general, no cure is available for jet lag. Instead, focus counseling on factors known from laboratory simulations to alter circadian timing. Until more randomized controlled trials of treatments prescribed before, during, or after transmeridian flights are published, focus on providing robust, evidence-based advice.
The following authors contributed to the previous version of this chapter: Greg Atkinson, Ronnie Henry, Alan M. Batterham, Andrew Thompson
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