Light-induced changes of the circadian clock of humans: increasing duration is more effective than increasing light intensity.

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.

• Authors: Karuna Dewan, Susan Benloucif, Kathryn Reid, Lisa F Wolfe, Phyllis C Zee
• Journal: Sleep (Sleep) Vol. 34 Issue 5 Pg. 593-9 (May 01 2011) ISSN: 1550-9109 [Electronic] United States
• PMID: 21532952 (Publication Type: Journal Article, Randomized Controlled Trial, Research Support, N.I.H., Extramural)

Chemical References

• Melatonin

Topics

• Adult
• Body Temperature (radiation effects)
• Circadian Rhythm (radiation effects)
• Dose-Response Relationship, Radiation
• Female
• Humans
• Light
• Male
• Melatonin (blood)
• Phototherapy (methods)
• Time Factors
• Young Adult