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Sharkey, K. M., Carskadon, M. A., Figueiro, M. G., Zhu, Y., & Rea, M. S. (2011). Effects of an advanced sleep schedule and morning short wavelength light exposure on circadian phase in young adults with late sleep schedules. Sleep Med, 12(7), 685–692.
Abstract: OBJECTIVE: We examined the effects of an advanced sleep/wake schedule and morning short wavelength (blue) light in 25 adults (mean age+/-SD=21.8+/-3 years; 13 women) with late sleep schedules and subclinical features of delayed sleep phase disorder (DSPD). METHODS: After a baseline week, participants kept individualized, fixed, advanced 7.5-h sleep schedules for 6days. Participants were randomly assigned to groups to receive “blue” (470nm, approximately 225lux, n=12) or “dim” (<1lux, n=13) light for 1h after waking each day. Head-worn “Daysimeters” measured light exposure; actigraphs and sleep diaries confirmed schedule compliance. Salivary dim light melatonin onset (DLMO), self-reported sleep, and mood were examined with 2x2 ANOVA. RESULTS: After 6days, both groups showed significant circadian phase advances, but morning blue light was not associated with larger phase shifts than dim-light exposure. The average DLMO advances (mean+/-SD) were 1.5+/-1.1h in the dim light group and 1.4+/-0.7h in the blue light group. CONCLUSIONS: Adherence to a fixed advanced sleep/wake schedule resulted in significant circadian phase shifts in young adults with subclinical DSPD with or without morning blue light exposure. Light/dark exposures associated with fixed early sleep schedules are sufficient to advance circadian phase in young adults.