Preflight adjustment to eastward travel: 3 days of advancing sleep with and without morning bright light

Abstract

Jet lag is caused by a misalignment between circadian rhythms and local destination time. As humans typically take longer to re-entrain after a phase advance than a phase delay, eastward travel is often more difficult than westward travel. Previous strategies to reduce jet lag have focused on shaping the perceived light-dark cycle after arrival, in order to facilitate a phase shift in the appropriate direction. Here we tested treatments that travelers could use to phase advance their circadian rhythms prior to eastward flight. Thus, travelers would arrive with their circadian rhythms already partially re-entrained to local time. We determined how far the circadian rhythms phase advanced, and the associated side effects related to sleep and mood. Twenty-eight healthy young subjects participated in 1 of 3 different treatments, which all phase advanced each subject's habitual sleep schedule by 1 h/day for 3 days. The 3 treatments differed in morning light exposure for the 1st 3.5 h after waking on each of the 3 days: continuous bright light (> 3000 lux), intermittent bright light (> 3000 lux, 0.5 h on, 0.5 off, etc.), or ordinary dim indoor light (< 60 lux). A phase assessment in dim light (< 10 lux) was conducted before and after the treatments to determine the endogenous salivary dim light melatonin onset (DLMO). The mean DLMO phase advances in the dim, intermittent, and continuous light groups were 0.6, 1.5, and 2.1 h, respectively. The intermittent and continuous light groups advanced significantly more than the dim light group (p < 0.01) but were not significantly different from each other. The side effects as assessed with actigraphy and logs were small. A 2-h phase advance may seem small compared to a 6- to 9-h time zone change, as occurs with eastward travel from the USA to Europe. However, a small phase advance will not only reduce the degree of re-entrainment required after arrival, but may also increase postflight exposure to phase-advancing light relative to phase-delaying light, thereby reducing the risk of antidromic re-entrainment. More days of preflight treatment could be used to produce even larger phase advances and potentially eliminate jet lag.

Figure 1

A diagram of the study protocol, for a 2300 to 0600 sleeper. This was the most common sleep schedule in the study. During the phase assessment sessions, saliva was sampled every 30 min in dim light (< 10 lux) for later determination of melatonin levels. On days 11–13, subjects received the phase-advancing treatment, their wake time was advanced by 1 h each morning, and they received continuous, intermittent, or dim light in the morning. The end of the treatment on each day is indicated by the brackets. The shaded area represents time within which subjects were permitted to nap; for this schedule, it was from 1130 to 1730.

Figure 2

Mean salivary melatonin profiles for the dim (n = 9), intermittent (n = 11), and continuous light groups (n = 8). Error bars represent SEs. In each graph; the mean melatonin profile during the baseline phase assessment is represented by the lighter line; the bold line represents the mean melatonin profile during the final phase assessment. Horizontal lines indicate the average DLMO threshold for each group. The mean melatonin profiles were constructed referencing each individual subject’s data to the time of their DLMO in the baseline phase assessment.

Figure 3

Total sleep time and sleep onset latency, from sleep logs and from wrist actigraphy during baseline (days 2–6) and during the phase-advancing treatment (days 11–13). Values are means ± SEs.