Joint associations of sleep duration and multimorbidity with all-cause mortality in US adults

Background Sleep duration has been linked to mortality in numerous studies, typically showing U- or J-shaped associations. However, most research evaluates sleep in isolation or within single disease contexts, without considering the broader burden of multimorbidity. We examined the joint association of sleep duration and multimorbidity severity with all-cause mortality in a nationally representative sample of US adults. Methods We conducted a prospective cohort study using data from the 2004 National Health Interview Survey linked to the National Death Index through 2019. Adults aged ≥ 18 years with complete data were included (n = 29,997). Sleep duration was categorized as 1–4, 5–6, 7–8 (reference), 9, and ≥ 10 hours. Multimorbidity burden was assessed using the Charlson Comorbidity Index (CCI), categorized as none and tertiles among those with ≥ 1 condition. Survey-weighted Cox proportional hazards models estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for the joint association between sleep duration and multimorbidity. Models were adjusted for sociodemographic and behavioral covariates. Sensitivity analyses excluded deaths occurring within the first 12 months of follow-up. Results During up to 15 years of follow-up, mortality risk increased progressively with higher multimorbidity burden across all sleep-duration categories. In crude models, both short and long sleep were associated with elevated mortality compared with 7–8 hours. After adjustment, associations for short sleep were attenuated, whereas long sleep remained consistently associated with higher mortality. Compared with adults sleeping 7–8 hours with no multimorbidity, those reporting ≥ 10 hours of sleep in the highest CCI category had substantially elevated mortality risk (adjusted HR 11.15, 95% CI 6.54–19.01). Results were similar after excluding deaths within the first year of follow-up. Conclusions Sleep duration and multimorbidity jointly influence mortality risk among US adults. Prolonged sleep, particularly among individuals with higher multimorbidity burden, was strongly associated with mortality. These findings highlight the importance of considering multimorbidity when interpreting sleep–mortality relationships.