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Sleep Med. 2011 Sep;12(8):805-7. doi: 10.1016/j.sleep.2011.02.005. Epub 2011 Aug 19.

Effectiveness of evening phototherapy for insomnia is reduced by bright daytime light exposure.

Author information

1
Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA 94305, United States. jzeitzer@stanford.edu

Abstract

OBJECTIVE:

To examine the effect of ambulatory daytime light exposure on phase delays and on the advances produced by timed exposure to bright evening or morning light.

METHODS:

As a subset of a larger study, 32 older (63.0 ± 6.43 years) adults with primary insomnia were randomized to an at-home, single-blind, 12-week, parallel-group study entailing daily exposure to 45 min of scheduled evening or morning bright (∼4000 lux) light. Light exposure patterns during the baseline and the last week of treatment were monitored using actigraphs with built-in illuminance detectors. Circadian phase was determined through analysis of in-laboratory collected plasma melatonin.

RESULTS:

Less daytime light exposure during the last week of treatment was significantly associated with larger phase delays in response to evening light (r's>0.78). Less daytime light exposure during the last week of treatment was also associated with a significant delay in wake time (r's>-0.75). There were no such relationships between light exposure history and phase advances in response to morning light.

CONCLUSIONS:

Greater light exposure during the daytime may decrease the ability of evening light, but not morning light, exposure to engender meaningful changes of circadian phase.

PMID:
21855408
PMCID:
PMC3176957
DOI:
10.1016/j.sleep.2011.02.005
[Indexed for MEDLINE]
Free PMC Article

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