People who suffer from both insomnia symptoms and excessive daytime sleepiness face a 32% higher risk of death and a 40% higher risk of cardiovascular events compared with those who have neither complaint, according to a large prospective study of nearly half a million UK Biobank participants published in Sleep Health.
The risk increase went beyond what would be expected from adding the individual effects of each symptom alone, indicating a synergistic interaction that makes the combination particularly dangerous.
What they found
Researchers led by Ruhan Wang at Wuhan University of Science and Technology analyzed 495,398 UK Biobank participants with valid baseline sleep data. Over a mean follow-up of 14.9 years (7.46 million person-years), there were 51,926 deaths (10,854 from CVD) and 51,299 incident cardiovascular events.
Participants were categorized into four groups based on self-reported symptoms: neither insomnia nor excessive daytime sleepiness (EDS), insomnia only, EDS only, and both insomnia and EDS.
Compared with the reference group (neither symptom):
- Insomnia only was associated with modestly elevated risk across all outcomes
- EDS only showed similarly modest elevations
- Insomnia + EDS was associated with:
- 32% higher all-cause mortality (HR 1.32, 95% CI 1.25-1.40)
- 28% higher CVD mortality (HR 1.28, 95% CI 1.14-1.43)
- 40% higher incident CVD (HR 1.40, 95% CI 1.32-1.49)
Additive interaction analyses confirmed a synergistic effect beyond the sum of individual risks. The relative excess risk due to interaction (RERI) was 0.19 for all-cause mortality and 0.20 for CVD incidence, both statistically significant.
Why it matters
Insomnia and daytime sleepiness are often assessed and treated as separate clinical concerns, but this study shows their co-occurrence carries disproportionate risk. The findings support a shift toward assessing sleep symptom profiles holistically, a patient who reports both trouble sleeping and feeling excessively tired during the day may warrant more aggressive cardiovascular risk management than one with either symptom alone.
The large sample size, long follow-up, and consistent results across multiple outcomes strengthen the case for treating the insomnia-sleepiness combination as a distinct high-risk phenotype.
Limits
The study relied on single-time-point, self-reported insomnia symptoms and daytime sleepiness, which may not capture chronic patterns or subtypes. Residual confounding is possible despite extensive multivariable adjustment. The UK Biobank cohort is healthier and less diverse than the general population, which may affect generalizability. Mechanistic pathways, whether the synergy operates through autonomic dysfunction, inflammation, circadian disruption, or shared genetics, were not addressed.
Bottom line
The combination of insomnia symptoms and excessive daytime sleepiness is associated with roughly one-third higher mortality and 40% higher cardiovascular risk, with evidence of a synergistic interaction. Clinicians should consider the co-occurrence of these symptoms a red flag warranting thorough cardiovascular assessment.
Source
Ruhan Wang et al. Associations of concurrent insomnia symptoms and excessive daytime sleepiness with mortality and incident cardiovascular disease. Sleep Health (2026). DOI: 10.1016/j.sleh.2026.05.007. PMID: 42315375.