The natural history of insomnia: Does sleep extension differentiate between those that do and do not develop chronic insomnia?

According to the "3P model" of insomnia, the variable that mediates the transition from acute insomnia (AI) to chronic insomnia is "sleep extension" (the behavioural tendency to expand sleep opportunity to compensate for sleep loss). In the present analysis, we sought to evaluate how time in bed (TIB) varies relative to the new onset of AI and chronic insomnia. A total of 1,248 subjects were recruited as good sleepers (GS). Subjects were monitored over 1 year with sleep diaries. State transitions were defined, a priori, for AI, recovered from AI (AI-REC), and for chronic insomnia (AI-CI). Two additional groupings were added based on profiles that were unanticipated: subjects that exhibited persistent poor sleep following AI (AI-PPS [those that neither recovered or developed chronic insomnia]) and subjects that recovered from chronic insomnia (CI-REC). All the groups (GS, AI-REC, AI-CI, AI-PPS and CI-REC) were evaluated for TIB differences with longitudinal mixed effects models. Post hoc analyses for the percentage of the groups that were typed as TIB "restrictors, maintainers, and expanders" were conducted using longitudinal mixed effects models and contingency analyses. Significant differences for pre-post AI TIB were not detected for the insomnia groups. Trends were apparent for the AI-CI group, which suggested that minor increases in TIB occurred weeks before the declared onset of AI. Additionally, it was found that a significantly larger percentage of AI-CI subjects engaged in sleep extension (as compared to GS). The present data suggest that transition from AI to chronic insomnia does not appear to be initiated by sleep extension and the transition may occur before the elapse of 3 months of ≥3 nights of sleep continuity disturbance. Given these findings, it may be that the mismatch between sleep ability and sleep opportunity is perpetuated over time given the failure to "naturally" engage in sleep restriction (as opposed to sleep extension).