If the duration of time to be spent at the travel destination is sufficiently long, strategic avoidance and exposure to light can facilitate re-entrainment and avoid an antidromic process (19). Burgess and Eastman have devised “jet lag plans” that allow one to determine whether a phase delay or phase advance is most desirable, depending on the number of time zones crossed (22,23). The first step in this process is to create a grid with concurrent listing of home and destination times. In the example depicted in Figure 13.2, the individual is traveling seven time zones east, which will require a phase advance. On day 0, a rectangle is drawn around the times representative of home-based sleep hours. A symbol (inverted triangle) is subsequently added to represent the MCBT, which serves as an inflection point to determine whether light exposure will delay or advance circadian rhythms (before or after the MCBT, respectively, see Fig. 13.3). The precise placement is based on known relationships between the MCBT and habitual wake time, resulting in positioning either 2 or 3 hours prior to sleep offset, depending upon whether one typically sleeps 7 or fewer hours or more than 7 hours, respectively (22,24). At the bottom of the grid, a rectangle is drawn to represent the desired sleep schedule at the traveler’s destination, with inclusion of an MCBT symbol with the same relationship to the wake time described above. The distance between the home and destination-based MCBT symbols is representative of the required degree of circadian realignment. Generally speaking, shifts earlier in time are required for eastward flights (as in Fig. 13.2), and shifts later in time are required for westward flights. Advances of 8 hours or more are more readily accomplished by phase delays, however, as shown in Figure 13.4 (22,25).

If advances are required, the MCBT symbol is drawn on day 1 in the same location as day 0. For each subsequent day, the symbol is moved 1 hour earlier, based upon approximations of maximal phase advances (11,23), until a clock time within 1 hour of the desired destination MCBT time is reached and/or satisfactory sleep and daytime functioning is achieved (see Fig. 13.2) (22). If delays are required, the MCBT symbol is drawn 2 hours later on day 1 than on day 0 (reflecting the greater ease at which delays are achieved) (11,23), with subsequent daily shifts in 2-hour increments, again until a clock time within 1 hour of the desired destination MCBT time is reached and/or satisfactory sleep and daytime functioning is achieved (Fig. 13.4) In instances of a desired phase advance, 3 hours of dark are required prior to the MCBT and 3 hours of light are required immediately after the MCBT (depicted as “D” and “L”, respectively, on Figs. 13.2 and 13.4), as predicted by the light phase response curve (PRC) (see Fig. 13.3). If attempting to delay circadian rhythms, the opposite light/dark patterns are sought, as depicted in Figure 13.4. As flight/layover patterns will likely not allow for strict adherence to these measures, they represent idealized scenarios for which one should strive.

Requirements for darkness can be accomplished with sleep, protective eyewear, or by remaining in a dark room. Light requirements can be met with outdoor exposure, with a commercial light box, or with a separate apparatus (e.g., goggles or visors), many of which are sufficiently portable so as to be suitable for travel. Light boxes are considered more effective in achieving phase shifts than alternative devices, however, and widely available blue-light equipment may confer greater benefit than previously realized (22,26,27).

Guidelines regarding preflight circadian advances have also been developed in anticipation of eastward travel (12,18,28). The goal of such an intervention is to reduce the risk of antidromic re-entrainment and to hasten circadian adaptation and dissipation of jet lag symptoms upon arrival at the travel destination. In this 3-day protocol, the sleep/wake schedule is advanced by 1 hour each day, and subjects are exposed to intermittent bright light for 3.5 hours upon awakening (mean intensity ∽5000 lux¹), administered as four 30-minute pulses, separated by 30 minutes in ordinary room light. Light administered in this fashion was found to be as effective as continuous bright light in a previous study (18), which has important practical implications. A synergistic response can be achieved by using concomitant melatonin (at a recommended chronobiotic dose of 0.5 mg), starting at 5 hours prior to habitual (home-based) bedtime (timed to achieve phase advances; see Fig. 13.3), with 1-hour incrementally earlier administration times, for resultant circadian advances of approximately 1-hour daily (compared with placebo) (25,28). Importantly, standardized assessments have revealed that this is not met with production of jet lag prior to departure, and can align the MCBT such that light exposure will properly facilitate completion of re-entrainment upon arrival to the travel destination (12,25). The same processes can be performed in preparation for a return flight, either predeparture or upon arrival. No pretravel guidelines have been published in anticipation of circadian delays (westward flights), and would be much more difficult to accomplish for those with inflexible work hours.

Caffeine is presumably the first-line “medication” utilized to combat jet-lag induced sleepiness, but only two controlled field studies are available to assess its efficacy. Both studies utilized slow-release preparations at a dosage of 300 mg. In the first, following an eastward flight traversing seven time zones, subjects took the pill at 08:00 destination time for a period of 5 days (41). Urine and saliva samples were tested serially to determine the degree of circadian re-entrainment. Although alertness and other jet lag symptoms were curiously not assessed, circadian rhythms (as determined by salivary cortisol levels) were re-entrained at a more rapid rate than placebo, and to a degree comparable to that achieved by exogenous melatonin. In a follow-up study by the same group, those receiving
caffeine demonstrated an objective decrease in sleepiness compared with the melatonin and placebo group (assessed by multiple sleep latency tests), but intergroup subjective differences were not identified (42). Furthermore, those receiving caffeine demonstrated a significant increase in both objective and subjective nocturnal sleep complaints.