Sleep Apnea and Short Sleep: Why Sleeping Less Than 6 Hours Could Be Deadly
Key Takeaways
- Event duration, not just event count, matters. A 2018 Sleep Heart Health Study analysis found that people whose apnea events were shortest in duration had a higher risk of all-cause mortality than those with longer events, even after adjusting for AHI. The standard AHI score alone can miss this kind of risk.¹
- COMISA (comorbid insomnia and sleep apnea) carries a distinct, measurable mortality signal. One cohort study found a crude mortality rate of 9.5 deaths per 1,000 person-years in COMISA patients, compared to 5.2 for OSA alone, 4.5 for insomnia alone, and 4.0 for neither condition.²
- Mild-to-moderate OSA isn't automatically lower risk. The event-duration effect was strongest specifically in people with moderate sleep apnea, not just severe cases, which is a reason not to skip treatment just because a diagnosis says "mild" or "moderate."¹
On This Page
Quick answer: Two separate bodies of research suggest your AHI score doesn't tell the whole story. First, a Sleep Heart Health Study analysis found that shorter individual apnea events, not longer ones, predicted higher mortality risk, likely because they reflect a lower arousal threshold and more frequent oxygen swings. Second, having both insomnia and sleep apnea together (COMISA) is linked to meaningfully higher mortality than either condition alone. Neither finding means "sleep less than 6 hours and you'll triple your heart disease risk." That specific claim isn't supported by the research it's often attached to.
Why AHI Alone Might Not Tell the Whole Story
For years, the Apnea-Hypopnea Index (AHI), how many times per hour your breathing stops or is significantly reduced, has been the primary way sleep specialists gauge OSA severity. Sleep apnea occurs when the airway collapses during sleep, causing the individual to periodically stop breathing; this is linked to a range of comorbidities, including high blood pressure, heart disease, and increased mortality risk.
But AHI counts how many events happen; it says nothing about how long each one lasts. A 2018 analysis of the Sleep Heart Health Study, a large community-based cohort, looked at exactly that question. Tracking over 5,700 participants across 11 years of follow-up, researchers found that people whose apnea events were shortest in duration had a significantly higher all-cause mortality risk (hazard ratio 1.31) than those with longer events, even after adjusting for AHI, smoking, and existing cardiometabolic disease.¹ The likely explanation: shorter events tend to reflect a lower arousal threshold, meaning the brain wakes the body up faster, which sounds protective but actually means more frequent, sharper oxygen desaturations over the course of a night. This effect was strongest in people with moderate sleep apnea, not just the most severe cases.¹
A "mild" or "moderate" AHI score doesn't automatically mean lower risk. Event duration is a factor most standard sleep reports don't highlight, which is one more reason not to defer treatment based on AHI severity alone.
The Other Half of the Picture: COMISA
Separate from event duration, there's a well-documented pattern where sleep apnea and insomnia occur together, now commonly called COMISA (Comorbid Insomnia and Sleep Apnea). Some people with OSA develop a secondary fear of falling asleep, subconsciously associating sleep with choking or gasping, and that fuels insomnia on top of the apnea itself.
COMISA carries higher mortality risk than either condition alone. A cohort study tracking mortality across these groups found a crude mortality rate of 9.5 deaths per 1,000 person-years among COMISA patients, compared to 5.2 for OSA alone, 4.5 for insomnia alone, and 4.0 for people with neither condition.² Other research has linked COMISA to higher rates of prevalent cardiovascular disease compared to either condition individually.²
Signs You Might Have COMISA
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You struggle to fall asleep despite being exhausted
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You wake up frequently and have trouble falling back asleep
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You use CPAP consistently but still get well under 7 hours of sleep most nights
What Actually Helps
Both threads of research point toward the same practical fix: consistent treatment, not a perfect AHI number.
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Treat the apnea first. Once CPAP therapy reliably keeps the airway open, many patients find the underlying fear of sleep driving secondary insomnia starts to ease.
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Consider CBT-I alongside CPAP. Cognitive Behavioral Therapy for Insomnia is used as a companion treatment for COMISA patients, targeting the insomnia component that CPAP alone doesn't treat.
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Don't skip therapy because your AHI is "only" mild or moderate. Given that the event-duration mortality effect was strongest in moderate cases, treatment consistency matters regardless of where your number falls on the severity scale.
Frequently Asked Questions
Does sleeping less than 6 hours triple your risk of dying from heart disease if you have sleep apnea?
That specific figure isn't well-supported by the research commonly cited for it. What is supported: short apnea event duration (a different measurement from total sleep time) independently predicts higher mortality risk, and the combination of insomnia and sleep apnea (COMISA) carries a meaningfully higher mortality rate than either condition alone.¹²
What's the difference between apnea event duration and short sleep duration?
Event duration is how long each individual breathing pause lasts, typically measured in seconds. Sleep duration is your total hours of sleep per night. They're different measurements from different research, and confusing the two can lead to misleading conclusions.
Can CPAP fix COMISA on its own?
CPAP addresses the apnea component, and many patients find their secondary insomnia improves once breathing is stabilized. But COMISA often benefits from combining CPAP with CBT-I, which directly targets the insomnia component CPAP alone isn't designed to treat.
Is mild sleep apnea actually risky, or just moderate and severe?
Research on event duration found the mortality association was strongest in people with moderate OSA, not just severe cases, so treatment shouldn't be deprioritized just because a diagnosis is labeled mild or moderate.¹
Conclusion
The most common and effective treatment for sleep apnea is CPAP therapy. However, some patients find the machine and the mask combo uncomfortable and choose not to use it if their sleep apnea is not severe. Mild or moderate sleep apnea patients are at a minimum, equal to or at greater risk of death as severe sufferers. CPAP remains the most effective and least invasive therapy available. Therefore, use it consistently in even the most moderate of cases.
The CPAP Shop has a team of experts ready to answer all your questions regarding CPAP therapy and products. Give us a call at 866-414-9700.
This article is for general informational purposes only and is not medical advice. If you have questions about sleep apnea, talk to your doctor so they can advise you based on your specific health history.
This post was updated with the latest information on September 22, 2026.
References
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Butler, M.P., et al. "Apnea–Hypopnea Event Duration Predicts Mortality in Men and Women in the Sleep Heart Health Study." American Journal of Respiratory and Critical Care Medicine, 2019. atsjournals.org/doi/abs/10.1164/rccm.201804-0758OC
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"Effects of Combined Morbid Insomnia and Sleep Apnea on Long-Term Cardiovascular Risk and All-Cause Mortality in Elderly Patients: A Prospective Cohort Study." PMC. pmc.ncbi.nlm.nih.gov/articles/PMC11265059
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Sweetman, A., Lack, L., Bastien, C. "Co-Morbid Insomnia and Sleep Apnea (COMISA): Prevalence, Consequences, Methodological Considerations, and Recent Randomized Controlled Trials." Brain Sciences, 2019. Referenced via "Comorbid Insomnia and Obstructive Sleep Apnea (COMISA): Current Concepts of Patient Management." PMC. pmc.ncbi.nlm.nih.gov/articles/PMC8430469
