Study objectives: This study examines the relevance of self-reported morning and evening chronotypes in treatment-seeking insomniacs presenting to a tertiary sleep clinic setting.
Design: Using a cross-sectional design, patients were categorized as morning, intermediate, and evening chronotypes based upon scores on the Morningness-Eveningness Composite Scale (MECS). Group comparisons were made on self-report measures of nocturnal sleep, sleep period variability, and waking correlates and consequences of insomnia.
Setting: Sleep disorders clinic
Patients: The sample consisted of 312 patients who presented to a group cognitive-behavior therapy for insomnia (CBT-I) at the sleep clinic.
Measurements and results: Participants completed the MECS, Beck Depression Inventory (BDI), Dysfunctional Beliefs and Attitudes about Sleep Scale (DBAS), and one week of sleep diary prior to treatment. Even after adjusting for total wake time as an index of insomnia severity, differences between the three chronotypes were present on several measures. Compared to the morning and intermediate types, evening types reported more total sleep time, more time in bed, greater variability in the time out of bed, and higher levels of distress on the DBAS and BDI.
Conclusions: These results indicate that insomniacs presenting to a sleep specialist who endorse an evening chronotype report sleep/wake irregularities and waking distress greater than expected in association with the level of insomnia severity. These factors may serve to perpetuate the insomnia disorder and might be particularly important to consider when treating this subgroup of insomniacs.