Clinical trials with light therapy (LT) for delayed sleep phase disorder (DSPD) are sparse and little is known about factors that are favorable for improvements. In this study, LT with scheduled rise times was conducted at home for 14 days by 44 participants with DSPD aged 16–26 years. Primary outcomes were sleep onset and sleep offset. Potential predictors were demographic characteristics, chronotype, dim light melatonin onset, the number of days the LT lamp was used, the daily duration of LT, daytime sleepiness, anxiety, depression, worry, and rumination. Significant advances were observed in sleep onset and sleep offset from baseline to the end of treatment. The number of days of LT predicted earlier sleep onset and sleep offset.
During puberty, there is a known delay in sleep–wake preference and circadian rhythm (Carskadon, Acebo, & Jenni, 2004Carskadon, M. A., Acebo, C., & Jenni, O. G. (2004). Regulation of adolescent sleep: Implications for behavior. Annals of the New York Academy of Sciences, 1021, 276–291.; Carskadon, Vieira, & Acebo, 1993 Carskadon, M. A., Vieira, C., & Acebo, C. (1993). Association between puberty and delayed phase preference. Sleep, 16, 258–262.). If this delay becomes persistent and causes a functional impairment, the person has developed delayed sleep phase disorder (DSPD). DSPD is most common among adolescents and young adults, and the prevalence is about 1–10% in this group (American Academy of Sleep Medicine, 2014 American Academy of Sleep Medicine. (2014). International classification of sleep disorders. Diagnostic and coding manual (3d ed.). Westchester, IL: Author.; Lovato, Gradisar, Short, Dohnt, & Micic, 2013 Lovato, N., Gradisar, M., Short, M., Dohnt, H., & Micic, G. (2013). Delayed sleep phase disorder in an Australian school-based sample of adolescents. Journal of Clinical Sleep Medicine, 9, 939–944.; Weitzman et al., 1981 Weitzman, E. D., Czeisler, C. A., Coleman, R. M., Spielman, A. J., Zimmerman, J. C., Dement, W.,… Pollak, C. P. (1981). Delayed sleep phase syndrome. A chronobiological disorder with sleep-onset insomnia. Archives of General Psychiatry, 38, 737–746.). This disorder often includes difficulties initiating sleep, fatigue, daytime sleepiness, concentration difficulties, irritability, depressive symptoms, and anxiety. Social consequences often related to DSPD are truancy, late arrival to school or work, substance abuse, and poor academic performance (Barion & Zee, 2007 Barion, A., & Zee, P. C. (2007). A clinical approach to circadian rhythm sleep disorders. Sleep Medicine, 8, 566–577.; Dagan, Stein, Steinbock, Yovel, & Hallis, 1998 Dagan, Y., Stein, D., Steinbock, M., Yovel, I., & Hallis, D. (1998). Frequency of delayed sleep phase syndrome among hospitalized adolescent psychiatric patients. Journal of Psychosomatic Research, 45, 15–20.; Dewald, Meijer, Oort, Kerkhof, & Bogels, 2010 Dewald, J. F., Meijer, A. M., Oort, F. J., Kerkhof, G. A., & Bogels, S. M. (2010). The influence of sleep quality, sleep duration and sleepiness on school performance in children and adolescents: A meta-analytic review. Sleep Medicine Reviews, 14, 179–189.; Lovato et al., 2013 Lovato, N., Gradisar, M., Short, M., Dohnt, H., & Micic, G. (2013). Delayed sleep phase disorder in an Australian school-based sample of adolescents. Journal of Clinical Sleep Medicine, 9, 939–944.; Ohta, Iwata, Kayukawa, & Okada, 1992 Ohta, T., Iwata, T., Kayukawa, Y., & Okada, T. (1992). Daily activity and persistent sleep-wake schedule disorders. Progress in Neuropsychopharmacology and Biological Psychiatry, 16, 529–537.; Saxvig, Pallesen, Wilhelmsen-Langeland, Molde, & Bjorvatn, 2012 Saxvig, I. W., Pallesen, S., Wilhelmsen-Langeland, A., Molde, H., & Bjorvatn, B. (2012). Prevalence and correlates of delayed sleep phase in high school students. Sleep Med, 13(2), 193–199.; Sivertsen, Harvey, Pallesen, & Hysing, 2015 Sivertsen, B., Harvey, A. G., Pallesen, S., & Hysing, M. (2015). Mental health problems in adolescents with delayed sleep phase: Results from a large population-based study in Norway. Journal of Sleep Research, 24, 11–18.; Sivertsen et al., 2013 Sivertsen, B., Pallesen, S., Stormark, K. M., Boe, T., Lundervold., A. E., & Hysing, M. (2013). Delayed sleep phase syndrome in adolescents: Prevalence and correlates in a large population based study. BMC Public Health, 13, 1663.; Sivertsen, Glozier, Harvey, & Hysing, 2015 Sivertsen, B., Glozier, N., Harvey, A. G., & Hysing, M. (2015). Academic performance in adolescents with delayed sleep phase. Sleep Medicine, 16, 1084–1090.; Thorpy, Korman, Spielman, & Glovinsky, 1988 Thorpy, M. J., Korman, E., Spielman, A. J., & Glovinsky, P. B. (1988). Delayed sleep phase syndrome in adolescents. Journal of Adolescent Health Care, 9, 22–27.).
Despite the distress and dysfunction caused by DSPD, motivation to start treatment and compliance to treatment are often problematic among persons with DSPD (Barion & Zee, 2007Barion, A., & Zee, P. C. (2007). A clinical approach to circadian rhythm sleep disorders. Sleep Medicine, 8, 566–577.). Bright light exposure in the morning is one of the recommended treatments for DSPD (Morgenthaler et al., 2007 Morgenthaler, T. I., Lee-Chiong, T., Alessi, C., Friedman, L., Aurora, R. N., Boehlecke, B.,… Zac, R. (2007). Standards of Practice Committee of the American Academy of Sleep Medicine: Practice parameters for the clinical evaluation and treatment of circadian rhythm sleep disorders [American Academy of Sleep Medicine report]. Sleep, 30, 1445–1459.). To date, there are no evidence-based guidelines for the duration of each LT session, the duration of the total treatment, the intensity of the lamp, or the exact timing in the morning of LT. In clinical practice, LT with bright white light for 30–45 min every morning is often recommended for patients with DSPD (Bjorvatn & Pallesen, 2009 Bjorvatn, B., & Pallesen, S. (2009). A practical approach to circadian rhythm sleep disorders. Sleep Medicine Reviews, 13, 47–60.). For optimal effect, LT in the morning should be combined with dim light in the evening (Hoban & Sulzman, 1985 Hoban, T. M., & Sulzman, F. M. (1985). Light effects on circadian timing system of a diurnal primate, the squirrel monkey. American Journal of Physiology, 249(2), R274–R280.; Rosenthal et al., 1990 Rosenthal, N. E., Joseph-Vanderpool, J. R., Levendosky, A. A., Johnston, S. H., Allen, R., Kelly, K. A.,… Starz, K. E. (1990). Phase-shifting effects of bright morning light as treatment for delayed sleep phase syndrome. Sleep, 13, 354–361.). LT is a safe treatment with only a few side effects that are generally mild and short-lived (Kogan & Guilford, 1998 Kogan, A. O., & Guilford, P. M. (1998). Side effects of short-term 10,000-lux light therapy. American Journal of Psychiatry, 155, 293–294.).
Most studies on the phase-advancing effects of LT on the circadian rhythm have been conducted in healthy subjects under strict laboratory conditions and focused on internal phase markers. These studies demonstrate that the circadian rhythm is affected by light through a phase-response curve. Light before the temperature nadir delays the circadian rhythm, and light after the temperature nadir advances the circadian rhythm (Boivin, Duffy, Kronauer, & Czeisler, 1996Boivin, D. B., Duffy, J. F., Kronauer, R. E., & Czeisler, C. A. (1996). Dose-response relationships for resetting of human circadian clock by light. Nature, 379(6565), 540–542.; Dewan, Benloucif, Reid, Wolfe, & Zee, 2011 Dewan, K., Benloucif, S., Reid, K., Wolfe, L. F., & Zee, P. C. (2011). Light-induced changes of the circadian clock of humans: Increasing duration is more effective than increasing light intensity. Sleep, 34, 593–599.; Khalsa, Jewett, Cajochen, & Czeisler, 2003 Khalsa, S. B., Jewett, M. E., Cajochen, C., & Czeisler, C. A. (2003). A phase response curve to single bright light pulses in human subjects. Journal of Physiology, 549(3), 945–952.; Minors, Waterhouse, & Wirz-Justice, 1991 Minors, D. S., Waterhouse, J. M., & Wirz-Justice, A. (1991). A human phase-response curve to light. Neuroscience Letter, 133, 36–40.; Revell, Molina, & Eastman, 2012 Revell, V. L., Molina, T. A., & Eastman, C. I. (2012). Human phase respose curve to intermittent blue light using a commercially available device. Journal of Physiology, 590(19), 4859–4868.). Bright light (10,000 lux) in a self-administered format has, in a randomized controlled trial, been shown to advance temperature nadir and decreases daytime sleepiness for persons with DSPD (Rosenthal et al., 1990 Rosenthal, N. E., Joseph-Vanderpool, J. R., Levendosky, A. A., Johnston, S. H., Allen, R., Kelly, K. A.,… Starz, K. E. (1990). Phase-shifting effects of bright morning light as treatment for delayed sleep phase syndrome. Sleep, 13, 354–361.). However, a recent study demonstrated that gradually advanced wake-up times combined with bright light (10,000 lux) did not have significantly better effect than gradually advanced wake-up times combined with orange light (400 lux) on sleep diary data and dim light melatonin onset (DLMO) in DSPD (Saxvig et al., 2014 Saxvig, I. W., Wilhelmsen-Langeland, A., Pallesen, S., Vedaa, O., Nordhus, I. H., & Bjorvatn, B. (2014). A randomized controlled trial with bright light and melatonin for delayed sleep phase disorder: Effects on subjective and objective sleep. Chronobiology International, 31, 72–86.).
The aim of the present study was to investigate the effect of self-administered LT with scheduled rise times on the sleep-wake rhythm and daytime functioning. In this study, we also wanted to examine possible predictors of the outcome. To our knowledge, predictors of the effect of scheduled LT in patients with DSPD have so far not been investigated. Daytime sleepiness, anxiety, and depression were investigated as predictors since they are common symptoms in DSPD. Worry and rumination were investigated as possible predictors as they are common clinical features in persons with sleep difficulties (Carney, Harris, Falco, & Edinger, 2013Carney, C. E., Harris, A. L., Falco, A., & Edinger, J. D. (2013). The relation between insomnia symptoms, mood, and rumination about insomnia symptoms. Journal of Clinical Sleep Medicine, 9, 567–575.; Carney, Harris, Moss, & Edinger, 2010 Carney, C. E., Harris, A. L., Moss, T. G., & Edinger, J. D., (2010). Distinguishing rumination from worry in clinical insomnia. Behavioral Research Therapy, 48, 540–546.). Since little is known about how LT should be administered at home, the number of days the LT lamp was used and the daily duration of LT were investigated as possible predictors. Time of DLMO and chronotype preference was investigated as possible predictors since they are measures of the delay in diurnal rhythm. Understanding predicting factors can be important to identify persons with DSPD that might need extra support during LT, and to isolate factors during LT that can improve the treatment response.
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