Abstract

Sleep disturbances are an all-too-familiar symptom of jet lag and a prime source of complaints for transmeridian travelers and flight crews alike. They are the result of a temporary loss of synchrony between an abruptly shifted sleep period, timed in accordance with the new local day-night cycle, and a gradually reentraining circadian system. Scheduled exposure to bright light can, in principle, alleviate the symptoms of jet lag by accelerating circadian reentrainment to new time zones. Laboratory simulations, in which sleep time is advanced by 6 to 8 h and the subjects exposed to bright light for 3 to 4 h during late subjective night on 2 to 4 successive days, have not all been successful. The few field studies conducted to date have had encouraging results, but their applicability to the population at large remains uncertain due to very limited sample sizes. Unresolved issues include optimal times for light exposure on the first as well as on subsequent treatment days, whether a given, fixed, light exposure time is likely to benefit a majority of travelers or whether Light treatment should be scheduled instead according to some individual circadian phase marker, and if so, can such a phase marker be found that is both practical and reliable.