Effects of cognitive behavior therapy for insomnia with adjunctive bright light therapy on sleep variability in youths with insomnia and eveningness: secondary analysis of a randomized controlled trial

Yue Pan, Forrest Tin Wai Cheung, Ngan Yin Chan, Joey Wing Yan Chan, Jihui Zhang, Albet Martin Li, Colin A. Espie, Michael Gradisar, Yun Kwok Wing, Shirley Xin Li

Abstract

Introduction: Insomnia is a common sleep complaint among youth, negatively impacting their physical and mental health. Youths with insomnia and evening chronotype, i.e., a circadian preference for later bedtime and rise time, tend to have more irregular sleep patterns, characterized by greater night-to-night sleep variability. Cognitive behavioral therapy for insomnia (CBT-I) and bright light therapy (BLT), a circadian-focused intervention, have been shown to improve sleep but their effects on reducing sleep variability in youths remained unclear. The present study aimed to explore the effects of CBT-I with adjunctive BLT on sleep variability in youths with insomnia and eveningness.

Materials and methods: This was a secondary analysis of a randomized controlled trial (Ref No. NCT04256915). Youths aged 12-24 years with insomnia disorder and eveningness were recruited and randomized to one of the three arms: 1) six weeks of CBT-I with adjunctive BLT (CBTI+BLT); 2) six weeks of CBT-I with placebo BLT (CBTI-BLT); 3) waitlist control (WL). All participants completed a 7-day sleep diary with actigraphy monitoring and self-reported questionnaires at pre-treatment and post-treatment, with additional follow-ups at one-month and six-month for the two treatment groups. Subjective and objective sleep variabilities were calculated using root mean squared successive differences from the sleep diary and actigraphy data.

Results: A total of 159 participants (mean age: 20.10 s.d. 2.20 years, 55% female) were randomized into three arms (CBTI+BLT: n = 54, CBTI-BLT: n = 53, WL: n = 52). A significant Time (pre-treatment vs. post-treatment) x Group (CBTI+BLT vs CBTI-BLT vs WL) interaction was observed for self-reported variability in sleep onset latency (SOL) (p = .035). CBTI-BLT resulted in a significantly greater reduction in self-reported SOL variability at post-treatment compared to WL (d = -0.71, p = .010). However, there were no significant differences in sleep variability parameters between CBTI+BLT and WL. In addition, no significant group x time interactions were found for sleep variability parameters at one- and six-month follow-ups between CBTI+BLT and CBTI-BLT. Within-group analyses indicated that reductions in SOL variability in the CBTI-BLT group were maintained at one-month (d = -0.74, p = .027) and six-month (d = -0.71, p = .020) follow-ups compared to baseline. Neither the improvement of depressive symptoms nor the change of circadian preference significantly mediated the effects of CBT-I on reduction of sleep variability.

Conclusions: The findings indicate that CBT-I significantly reduced variability in sleep onset latency, with effects maintained at one-month and six-month follow-ups. Future research should investigate the specific mechanisms underlying the effects of CBT-I on sleep variability.

Acknowledgments: This work was partly supported by the General Research Fund from the Hong Kong Research Grants Council awarded to SXL (Ref. 17608918) and the Seed Fund for Basic Research from the University Research Committee awarded to SXL.

Recommended citation: Pan, Y., Cheung, F. T. W., Chan, N. Y., Chan, J. W. Y., Zhang, J., Li, A. M., Espie, C. A., Gradisar, M., Wing, Y.-K., & Li, S. X. (2026). Effects of cognitive behavior therapy for insomnia with adjunctive bright light therapy on sleep variability in youths with insomnia and eveningness: secondary analysis of a randomized controlled trial. Sleep Medicine, 138, 107302. https://doi.org/10.1016/j.sleep.2025.107302