Work

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

Year: 2011

Type: article

Study designs: Randomized Controlled Trial, Clinical Trial

Abstract: 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.

Source: SLEEP

DOI: 10.1093/sleep/34.5.593

Authors: Karuna Dewan, Susan Benloucif, Kathryn Reid, Lisa F. Wolfe, Phyllis C. Zee

Institutions: Baylor College of Medicine, Northwestern University

Language: English

Topic: Circadian rhythm and melatonin

Subfield: Endocrine and Autonomic Systems

Field: Neuroscience

Domain: Life Sciences

SDG: Good health and well-being

Open Access status: bronze

Funders: National Institute on Aging, National Heart, Lung, and Blood Institute, National Center for Research Resources