Nonrestorative sleep mediates eveningness and insomnia severity

Abstract

Possessing an evening circadian preference is associated with greater subjective sleep disturbance. The present study sought to determine whether day-to-day restoration from sleep upon waking mediates the relation between eveningness and general insomnia symptomology, as well as whether this association occurs independently of quantitative sleep impairment. Late adolescent college students (N = 164) completed retrospective measures of chronotype and insomnia severity, as well as daily restorative sleep questionnaires and sleep diaries over a 2-week sampling period. Path analysis examined the direct effects of chronotype, restorative sleep, and nighttime sleep efficiency on insomnia symptomology, and the indirect effect of chronotype through restorative sleep. Chronotype’s indirect effect via restorative sleep accounted for 66.18% of its total effect on insomnia severity, and its non-significant direct path was thus discarded. The final specified path model displayed strong fit to the data and predicted insomnia severity from two pathways: greater eveningness via nonrestorative sleep as a mediator, and lower sleep efficiency. Lack of restoration from sleep upon waking is a potent mediator of the established relation between eveningness and self-reported insomnia severity. Future studies may generalize this finding to other populations, particularly those vulnerable to circadian phase delay or disruption.