The joint association of sleep duration and insomnia symptoms with disability retirement--a longitudinal, register-linked study.

OBJECTIVE: The aim of this study was to examine the joint association of sleep duration and insomnia symptoms with subsequent disability retirement.
METHODS: Baseline survey data were collected in 2000-2002 from 40-60-year-old employees of the City of Helsinki, all working at baseline. Baseline data were linked with disability retirement data until the end of 2010, obtained from the Finnish Centre for Pensions registers (N=6042). Sleep duration and self-reported insomnia symptoms (non-restorative sleep and difficulties in initiating and maintaining sleep) were derived from the baseline surveys. All-cause disability retirement (N=561) and the most prevalent diagnostic groups - musculoskeletal diseases (43%) and mental disorders (26%) - were examined. Cox regression analysis was used to yield hazard ratios (HR) with 95% confidence intervals (95% CI).
RESULTS: A joint association of sleep duration and insomnia symptoms with disability retirement was found, implying a higher risk for those with frequent insomnia symptoms. HR for all-cause disability retirement ranged among those with frequent symptoms from 2.02 (95% CI 1.53-2.68, sleeping 7 hours) to 3.92 (95% CI 2.57-5.97, sleeping ≤ 5 hours). Adjusting for sociodemographic, work, and health-related factors attenuated the associations, which nevertheless remained. The associations were similar for the two diagnostic groups, although stronger for those with mental disorders.
CONCLUSION: Frequent insomnia symptoms dominate the joint association of sleep duration and insomnia symptoms with subsequent disability retirement. Examining exclusively sleep duration would provide an incomplete understanding of the consequences of poor sleep.