Advanced sleep schedules affect circadian gene expression in young adults with delayed sleep schedules

Background: Human circadian rhythms are regulated by the interplay between circadian genes and environmental stimuli. The influence of altered sleep-wake schedules or light on human circadian gene expression patterns is not well characterized. Methods: Twenty-one young adults were asked to keep to their usual sleep schedules and two blood samples were drawn at the end of the first week from each subject based on estimated time of dim light melatonin onset (DLMO); the first sample was obtained one and a half hours before the estimated DLMO and the second three hours later, at one and a half hours after the estimated DLMO. During the second week, participants were randomized into two groups, one that received a one hour blue-light (lambda(max) = 470 nm) exposure in the morning and one that received a comparable morning dim-light exposure. Two blood samples were obtained at the same clock times as the previous week at the end of the second week. Results: We measured the expression of 10 circadian genes in response to sleep-wake schedule advancement and morning blue-light stimulation in the peripheral blood of 21 participants during a two-week field study. We found that nine of the 10 circadian genes showed significant expression changes from the first to the second week for participants in both the blue-light and dim-light groups, likely reflecting significant advances in circadian phase. Conclusions: This wholesale change in circadian gene expression may reflect considerable advances in circadian phase (i.e., advance in DLMO) from the first to the second week resulting from the advanced, daily personal light exposures. (c) 2013 Elsevier B.V. All rights reserved.