Chapter 8 Travel by Air, Land & Sea
RISK FOR TRAVELERS
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, clinicians should first determine how many time zones the traveler will cross and what the discrepancy will be between time of day at home and at the destination. During the first few days after a flight to a new time zone, a person’s circadian rhythms are still “anchored” to time of day at home. Rhythms then adjust gradually to the new time zone. A useful web-based tool for world time zone travel information can be found at www.timeanddate.com/worldclock/converter.html. If ≤3 time zones are being crossed, any symptoms such as tiredness are likely due to travel fatigue rather than significant jet lag, and will soon abate.
Many people traveling >3 time zones away for a vacation accept the risk of jet lag as a transient and mild inconvenience, while other people who are traveling on business or to compete in athletic events desire clear advice on prophylactic measures and treatments. If ≤2 days are spent in the new time zone, some people may prefer to anchor their sleep-wake schedule to time of day at home as much as is practical. Thereby, the total “burden” of jet lag resulting from the short round trip is minimized.
The symptomatology of jet lag can often be difficult to define because of variation between people, but also because the same person can experience different symptoms after each flight. Jet-lagged travelers typically experience ≥1 of the following symptoms after a flight across >3 time zones:
- Poor sleep, including 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)
- Poor performance in physical and mental tasks during the new daytime
- Negative feelings such as fatigue, headache, irritability, anxiety, inability to concentrate, and depression
- Gastrointestinal disturbances and decreased interest in, and enjoyment of, meals
- Symptoms are difficult to distinguish from the general fatigue resulting from international travel itself, as well as from other travel factors such as the hypoxia in the aircraft cabin.
Since light and social contacts influence the timing of internal circadian rhythms, a traveler who is staying in the time zone for >2 days should try to follow the local people’s sleep-wake habits as much as possible and as quickly as possible. This approach can be supplemented with the following information on specific treatments.
Exposure to bright light can advance or delay human circadian rhythms depending on when it is received relative to a person’s body clock time. Consequently, schedules have been formulated for proposed “good” and “bad” times for exposure to light after arrival in a new time zone (www.caa.co.uk/Passengers/Before-you-fly/Am-I-fit-to-fly/Health-information-for-passengers/Jet-lag/).
After flights that cross a large number of time zones, the proposed best circadian time for exposure to light immediately after the flight may actually be when it is still dark in the new time zone, which raises the question of whether exposure to supplementary light from a “light box” is helpful. Unfortunately, to date, only 1 small randomized controlled trial on supplementary bright light for reducing jet lag has been conducted. No clinically relevant effects of supplementary light on jet lag symptoms were detected after a flight across 5 time zones going west.
Diet and Physical Activity
Most dietary interventions have not been found to reduce jet lag symptoms. In a recent study, long-haul flight crews showed a small improvement in their general subjective rating of jet lag, but not the separate symptoms of jet lag or alertness, on their days off work when they adopted more regular meal times. Because gastrointestinal disturbance is a common symptom, smaller meals before and during the flight might be better tolerated than larger meals. Caffeine and physical activity may be used strategically at the destination to ameliorate any daytime sleepiness, but little evidence indicates that these interventions reduce overall feelings of jet lag. Any purported treatments that are underpinned by homeopathy, aromatherapy, and acupressure have no scientific basis.
Prescription medications like temazepam, zolpidem, or zopiclone may reduce sleep loss during and after travel but do not necessarily help resynchronize circadian rhythms or improve overall jet lag symptoms. If indicated, the lowest effective dose of a short-to medium-acting compound should be prescribed for the initial few days, bearing in mind the adverse effects of these drugs.
Taking hypnotics during a flight should be considered with caution because the resulting immobility could increase the risk of deep vein thrombosis. Alcohol should not be used by travelers as a sleep aid, because it disrupts sleep and can provoke obstructive sleep apnea.
Melatonin and Melatonin-Receptor Analogs
Melatonin is secreted at night by the pineal gland and is probably the most well-known treatment for jet lag. 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 melatonin products advise travelers to take it before nocturnal sleep in the new time zone, irrespective of number of time zones crossed or direction of travel. Studies published in the mid-1980s indicated a substantial benefit of melatonin (just before sleep) for reducing overall feelings of jet lag after flights. However, subsequent larger studies did not replicate the earlier findings.
Melatonin is considered a dietary supplement in the United States and is not regulated by the Food and Drug Administration. Therefore, the advertised concentration of melatonin has not been confirmed for most melatonin products on the market, and the presence of contaminants in the product cannot be ruled out.
Ramelteon, a melatonin-receptor agonist, is an FDA-approved treatment for insomnia. A dose of 1 mg 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 effects of the medication on other symptoms of jet lag and the timing of circadian rhythms are not as clear.
Multiple therapies to decrease jet lag symptoms may be combined into treatment packages. Although marginal gains from multiple treatments may aggregate, evidence from robust randomized controlled trials is lacking for most of these treatment packages. One treatment package offering tailored advice via a mobile application was piloted to be used over several months of frequent flying. Participants reported reduced fatigue compared with the comparator group and improved aspects of health-related behavior such as physical activity, snacking, and sleep quality but not other measures of sleep (latency, duration, use of sleep-related medication).
In conclusion, there is still no “cure” for jet lag. Counseling should focus on the factors that are known, from laboratory simulations, to alter circadian timing. Nevertheless, more randomized controlled trials of treatments prescribed before, during, or after transmeridian flights are needed before the clinician can provide robust, evidence-based advice.
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