Timing Light Treatment for Eastward and Westward Travel Preparation

Abstract

Jet lag degrades performance and operational readiness of recently deployed military personnel and other travelers. The objective of the studies reported here was to determine, using a narrow bandwidth light tower (500 nm), the optimum timing of light treatment to hasten adaptive circadian phase advance and delay. Three counterbalanced treatment order, repeated measures studies were conducted to compare melatonin suppression and phase shift across multiple light treatment timings. In Experiment 1, 14 normal healthy volunteers (8 men/6 women) aged 34.9+/-8.2 yrs (mean+/-SD) underwent light treatment at the following times: A) 06:00 to 07:00 h, B) 05:30 to 07:30 h, and C) 09:00 to 10:00 h (active control). In Experiment 2, 13 normal healthy subjects (7 men/6 women) aged 35.6+/-6.9 yrs, underwent light treatment at each of the following times: A) 06:00 to 07:00 h, B) 07:00 to 08:00 h, C) 08:00 to 09:00 h, and a no-light control session (D) from 07:00 to 08:00 h. In Experiment 3, 10 normal healthy subjects (6 men/4 women) aged 37.0+/-7.7 yrs underwent light treatment at the following times: A) 02:00 to 03:00 h, B) 02:30 to 03:30 h, and C) 03:00 to 04:00 h, with a no-light control (D) from 02:30 to 03:30 h. Dim light melatonin onset (DLMO) was established by two methods: when salivary melatonin levels exceeded a 1.0 pg/ml threshold, and when salivary melatonin levels exceeded three times the 0.9 pg/ml sensitivity of the radioimmunoasssy. Using the 1.0 pg/ml DLMO, significant phase advances were found in Experiment 1 for conditions A (p < .028) and B (p < 0.004). Experiment 2 showed significant phase advances in conditions A (p < 0.018) and B (p < 0.003) but not C (p < 0.23), relative to condition D. In Experiment 3, only condition B (p < 0.035) provided a significant phase delay relative to condition D. Similar but generally smaller phase shifts were found with the 2.7 pg/ml DLMO method. This threshold was used to analyze phase shifts against circadian time of the start of light treatment for all three experiments. The best fit curve applied to these data (R(2) = 0.94) provided a partial phase-response curve with maximum advance at approximately 9-11 h and maximum delay at approximately 5-6 h following DLMO. These data suggest largest phase advances will result when light treatment is started between 06:00 and 08:00 h, and greatest phase delays will result from light treatment started between 02:00 to 03:00 h in entrained subjects with a regular sleep wake cycle (23:00 to 07:00 h).

Circadian Variation of Melatonin, Light Exposure, and Diurnal Preference in Day and Night Shift Workers of Both Sexes

“…In experimental studies, light-at-night suppresses melatonin in a dose-response manner; however, even low intensities of light exposure (100 lux) are able to both suppress and phase shift the human melatonin rhythm (8). Not only intensity, but also timing of light exposure is important for the direction of the aMT6s phase shift, as described by the phase-response curve (45,46). We not only examined the phase shifting abilities of light exposures occurring during the night shift, but also tested the time period immediately after the shift and up to initiation of sleep and results were similar when morning light was taken into account.…”

Shift Work, Chronotype, and Melatonin Patterns among Female Hospital Employees on Day and Night Shifts

“…Furthermore, even though individual light exposure measures were not included in this study, our previous studies in these hospitals have shown that night lighting is quite dim at 40 to 50 lux (43,50), which is much lower than experimental conditions. Because intensity and timing of light exposures can impact melatonin patterns (51)(52)(53), individual light assessment should be incorporated in future studies. Finally, the modeling of time-series data by cosinor analysis did not take into account serial correlation of observations within participants, which may violate the assumption of homoscedasticity of error terms.…”

Phase advance with separate and combined melatonin and light treatment

“…The 3 mg SR melatonin was ingested at times based on established melatonin PRCs for optimum phase advance Lewy et al 1998;Revell and Eastman 2005). When morning light treatment was administered without melatonin the previous afternoon, its timing was based on established light PRCs (Khalsa et al 2003;Paul et al 2009;Revell and Eastman 2005). When morning light treatment was given after melatonin treatment the previous afternoon, we anticipated up to an hour advance of circadian phase due to the afternoon melatonin treatment.…”

“…Both exogenous melatonin and light treatment can shift circadian rhythms forward or backward according to phaseresponse curves (PRC) which define the optimum treatment times for phase advance and phase delay (Lewy et al 1998;Paul et al 2009;Revell and Eastman 2005).…”