Abstract
STUDY OBJECTIVES: Recent evidence indicates that daytime sleep disturbance associated with night shift work may arise from both circadian misalignment and sleep reactivity to stress. This presents an important clinical challenge because there are limited means of predicting and distinguishing between the two mechanisms, and the respective treatments differ categorically; however, there is support that a polymorphism in the PERIOD3 gene (PER3) may indicate differences in vulnerability to daytime sleep disturbance in shift workers. METHODS: We recruited 30 fixed night shift workers for laboratory assessments of circadian misalignment (dim light melatonin onset), sleep reactivity to stress (Ford Insomnia Response to Stress Test), daytime sleep disturbance (daytime Insomnia Severity Index), and PER3 genotype (PER3(4/4), PER3(5/-)). The two mechanisms for daytime sleep disturbance (circadian misalignment and sleep reactivity to stress) were compared between PER3 genotypes. RESULTS: Disturbed daytime sleep in the PER3(4/4) group was more likely related to sleep reactivity to stress, whereas disturbed sleep in the PER3(5/-) group was more likely related to circadian misalignment. Exploratory analyses also revealed a blunted melatonin amplitude in the PER3(4/4) genotype group. CONCLUSIONS: This study provides further evidence for multiple mechanisms (ie, circadian misalignment versus sleep reactivity to stress) associated with daytime sleep disturbances in shift workers. Additionally, it provides the new finding that PER3 genotype may play an important role in individual vulnerability to the different mechanisms of daytime sleep disturbance in night shift workers.