SLEEP - Light-Induced Changes of the Circadian Clock of Humans: Increasing Duration is More Effective than Increasing Light Intensity

VOLUME 34, ISSUE 05

LIGHT-INDUCED CHANGES IN THE CIRCADIAN CLOCK OF HUMANS
Light-Induced Changes of the Circadian Clock of Humans: Increasing Duration is More Effective than Increasing Light Intensity

Karuna Dewan, MD¹; Susan Benloucif, PhD²; Kathryn Reid, PhD²; Lisa F. Wolfe, MD³; Phyllis C. Zee, MD, PhD²

¹Department of Otolaryngology Head and Neck Surgery, The Baylor College of Medicine, Houston, TX; ²Department of Neurology, Chicago, IL; ³Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, IL

Table of Contents

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Study Objectives:

To evaluate the effect of increasing the intensity and/or duration of exposure on light-induced changes in the timing of the circadian clock of humans.

Design:

Multifactorial randomized controlled trial, between and within subject design

Setting:

General Clinical Research Center (GCRC) of an academic medical center

Participants:

56 healthy young subjects (20-40 years of age)

Interventions:

Research subjects were admitted for 2 independent stays of 4 nights/3 days for treatment with bright or dim-light (randomized order) at a time known to induce phase delays in circadian timing. The intensity and duration of the bright light were determined by random assignment to one of 9 treatment conditions (duration of 1, 2, or 3 hours at 2000, 4000, or 8000 lux).

Measurements and Results:

Treatment-induced changes in the dim light melatonin onset (DLMO) and dim light melatonin offset (DLMOff) were measured from blood samples collected every 20-30 min throughout baseline and post-treatment nights. Comparison by multi-factor analysis of variance (ANOVA) of light-induced changes in the time of the circadian melatonin rhythm for the 9 conditions revealed that changing the duration of the light exposure from 1 to 3 h increased the magnitude of light-induced delays. In contrast, increasing from moderate (2,000 lux) to high (8,000 lux) intensity light did not alter the magnitude of phase delays of the circadian melatonin rhythm.

Conclusions:

Results from the present study suggest that for phototherapy of circadian rhythm sleep disorders in humans, a longer period of moderate intensity light may be more effective than a shorter exposure period of high intensity light.

Citation:

Dewan K; Benloucif S; Reid K; Wolfe LF; Zee PC. Light-induced changes of the circadian clock of humans: increasing duration is more effective than increasing light intensity. SLEEP 2011;34(5):593-599.