Light Exposure Among Adolescents With Delayed Sleep Phase Disorder: A Prospective Cohort Study

Abstract

The objective of this study was to compare light exposure and sleep parameters between adolescents with delayed sleep phase disorder (DSPD; n = 16, 15.3 ± 1.8 yrs) and unaffected controls (n = 22, 13.7 ± 2.4 yrs) using a prospective cohort design. Participants wore wrist actigraphs with photosensors for 14 days. Mean hourly lux levels from 20:00 to 05:00 h and 05:00 to 14:00 h were examined, in addition to the 9-h intervals prior to sleep onset and after sleep offset. Sleep parameters were compared separately, and were also included as covariates within models that analyzed associations with specified light intervals. Additional covariates included group and school night status. Adolescent delayed sleep phase subjects received more evening (p < .02, 22:00–02:00 h) and less morning (p < .05, 08:00–09:00 h and 10:00–12:00 h) light than controls, but had less pre-sleep exposure with adjustments for the time of sleep onset (p < .03, 5–7 h prior to onset hour). No differences were identified with respect to the sleep offset interval. Increased total sleep time and later sleep offset times were associated with decreased evening (p < .001 and p = .02, respectively) and morning (p = .01 and p < .001, respectively) light exposure, and later sleep onset times were associated with increased evening exposure (p < .001). Increased total sleep time also correlated with increased exposure during the 9 h before sleep onset (p = .01), and a later sleep onset time corresponded with decreased light exposure during the same interval (p < .001). Outcomes persisted regardless of school night status. In conclusion, light exposure interpretation requires adjustments for sleep timing among adolescents with DSPD. Pre- and post-sleep light exposures do not appear to contribute directly to phase delays. Sensitivity to morning light may be reduced among adolescents with DSPD. (Author correspondence: [email protected])

Keywords:

• Adolescents
• Circadian
• Delayed sleep phase disorder
• Light
• Sleep

ACKNOWLEDGMENTS

This publication was made possible by grant 1 UL1 RR024150 from the National Center for Research Resources (NCRR), a component of the U.S. National Institutes of Health (NIH), and the NIH Roadmap for Medical Research. Its contents are solely the responsibility of the authors and do not necessarily represent the official view of NCRR or NIH. Information on NCRR is available at http://www.ncrr.nih.gov/. Information on Reengineering the Clinical Research Enterprise can be obtained from http://nihroadmap.nih.gov. The authors wish to thank the Rochester Minnesota Public School District for their support of this project (with particular thanks to Jeffrey Lunde), Christina Suh for assistance with creation of figures, and Lori Solmonson for administrative and technical assistance.

Declaration of Interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Notes

All lux model outcomes were transformed to the log(lux + 1) scale to better approximate model assumptions and to bound values away from 0 (or logged values away from negative infinity). Associations between the covariates and lux outcomes are presented as percent changes of lux + 1 with 95% confidence intervals (CIs).

When the nightly sleep summary variables were used as model outcomes, they were kept on their original scales, since the model assumptions were approximately true. Thus, linear slopes with 95% CIs are presented as summaries of the associations between the covariates and sleep parameters. Sleep onsets were shifted by −12 h to avoid the issue of values occurring on both sides of midnight, where the 24-h clock time resets to 0. Shifting the onset times by −12 h gives the correct mathematical distance between the onset hours (e.g., values of 23.5 and 1.5 were shifted to 11.5 and 13.5, respectively). When the onset/offset time variables were used as model covariates, both the 24-h onset and offset times were shifted by −12 h to give correct onset time distances around midnight and to preserve the distances between the onset and offset times relative to each other.