Phase advancing the human circadian clock with blue-enriched polychromatic light

Abstract

Background: Previous studies have shown that the human circadian system is maximally sensitive to short-wavelength (blue) light. Whether this sensitivity can be utilized to increase the size of phase shifts using light boxes and protocols designed for practical settings is not known. We assessed whether bright polychromatic lamps enriched in the short-wavelength portion of the visible light spectrum could produce larger phase advances than standard bright white lamps.

Methods: Twenty-two healthy young adults received either a bright white or bright blue-enriched 2-h phase advancing light pulse upon awakening on each of four treatment days. On the first treatment day the light pulse began 8h after the dim light melatonin onset (DLMO), on average about 2h before baseline wake time. On each subsequent day, light treatment began 1h earlier than the previous day, and the sleep schedule was also advanced.

Results: Phase advances of the DLMO for the blue-enriched (92+/-78 min, n=12) and white groups (76+/-45 min, n=10) were not significantly different.

Conclusion: Bright blue-enriched polychromatic light is no more effective than standard bright light therapy for phase advancing circadian rhythms at commonly used therapeutic light levels.

Figures

Figure 1

Representative protocol for a subject sleeping 00:00 - 8:00 at baseline. Grey bars indicate circadian phase assessments. Upward and downward arrows within the grey bars depict the DLMO and DLMOff, respectively. Rectangles with L's represent the times of the 2 h light pulses, which began 8 h after the baseline DLMO on the first treatment day, and began one hour earlier on each subsequent treatment day. In the text, day numbers correspond to the rows in this figure, between 12:00 and 12:00.

Figure 2

Spectral power distribution of the 4,100 K white lamps (dotted line) and 17,000 K blue-enriched lamps (solid line). The spectral plots overlap at ~550nm.

Figure 3

Phase advance of DLMO (circles) and DLMOff (squares) for individual subjects receiving bright blue-enriched or bright white light treatment. Lines represent the mean.

Figure 4

Scatterplot showing phase shift versus the start time of light treatment on day 25. Subjects receiving blue-enriched light are represented by filled circles, and subjects receiving white light are represented by open circles. Earlier awakenings this first day of light treatment, and thus all light treatment days, were associated with larger phase advances.

Figure 5

Subjective well-being ratings for the components of the “How Are You Feeling Right Now?” questionnaire (panels A-G) and the Columbia Jet Lag Scale (panel H) when undergoing phase advancing light treatment. All scores are shown as difference from baseline days 1-10. Panels A-G show the average of the four daily ratings. ANOVA results for the main effect of group are shown for each component. There were no significant main effects of group or group interaction effects.