Sleep disturbances as early indicators of incident psychiatric disease.

PURPOSE: Sleep disturbances are common in individuals with psychiatric diseases and may emerge years before diagnosis. It remains unclear whether they reflect modifiable risk factors or early manifestations of psychiatric illness. We aimed to investigate how different sleep dimensions relate to the risk of subsequent psychiatric illness, and how sleep symptoms evolve before and after diagnosis. METHODS: We analyzed data from 24,038 participants in the Swedish Longitudinal Occupational Survey of Health (2010-2018), linked to national health registers. Associations between baseline sleep characteristics and incident psychiatric diagnoses were estimated using Cox proportional hazards models. Symptom trajectories were modelled using non-linear mixed-effects models on a backward timescale centered at diagnosis. RESULTS: A total of 716 participants (2.9%) were diagnosed with a psychiatric disorder during follow-up. There was a U-shaped association between sleep duration and incident psychiatric illness. All sleep-related symptoms were associated with increased risk, with the strongest association observed for mental fatigue (HR 2.09, 95% CI 1.77-2.48). Insufficient sleep and sleep-disordered breathing were more common among those who later developed psychiatric illness, with differences remaining relatively stable over time. In contrast, other sleep complaints, such as insomnia symptoms and fatigue, progressively worsened prior to diagnosis and improved thereafter, although levels remained elevated compared to unaffected individuals. Long sleep duration and delayed wake-up times were exceptions, showing continued worsening post-diagnosis. CONCLUSION: Gradually intensifying sleep disturbances may reflect emerging psychiatric vulnerability consistent with a prodromal phase. Where repeated monitoring is feasible, these symptoms could serve as early warning signs to guide preventive efforts.