Two sleep disorders that are often treated as separate — and sometimes minor — problems may be far more dangerous together than either is alone, according to a pair of large studies out of Yale that have sleep researchers rethinking how they screen patients.
The condition, known as COMISA (comorbid insomnia and sleep apnea), occurs when a person struggles to fall or stay asleep and repeatedly stops breathing during the night. Individually, insomnia and obstructive sleep apnea are common and often manageable. Together, researchers found, they appear to compound each other’s risks rather than simply add to them.
In a study of nearly a million U.S. military veterans published in the Journal of the American Heart Association, Yale researchers found that COMISA dramatically raised the risk of hypertension and cardiovascular disease compared with either condition alone. “We spend an enormous amount of time managing cardiovascular disease downstream, but far less time addressing more upstream modifiable risk factors,” said Allison Gaffey, an assistant professor of medicine in cardiovascular medicine at Yale School of Medicine and the study’s first author. “Sleep disturbances, which are common in the veteran population, are often treated as secondary problems.”
A follow-up analysis presented in June at the SLEEP 2026 annual meeting in Baltimore extended the findings to metabolic disease. Drawing on data from more than one million veterans, researchers led by Karam Al Jumaily, a clinical sleep medicine fellow at Yale, found that insomnia alone was associated with a 41 percent increased risk of developing type 2 diabetes — a risk that was notably higher in women (48 percent) than men (39 percent). Sleep apnea alone carried a far steeper risk on its own, more than quintupling diabetes risk in men and nearly quadrupling it in women.
But it was the combination that stood out. Veterans with both conditions had an overall hazard of developing diabetes that was 6.2 times higher than veterans with neither disorder — a statistically significant interaction effect, meaning the two conditions appear to actively amplify one another rather than simply overlap. The elevated risk held up even after researchers adjusted for body mass index, smoking, hypertension, psychiatric conditions, and substance use, and the pattern showed up in younger veterans as well as older ones.
“COMISA represents an important sleep phenotype that clinicians and public health practitioners should be aware of, especially in veteran populations where sleep disorders and metabolic disease frequently overlap,” Al Jumaily said. “These findings underscore the potential value of early sleep disorder screening and intervention as part of diabetes prevention efforts.”
Part of what makes COMISA tricky clinically is that its two components can mask each other. Someone who can’t fall asleep may not stay asleep long enough for apnea episodes to be obvious, while apnea-driven awakenings can be mistaken for ordinary insomnia. Researchers say the findings make a case for screening patients for both conditions simultaneously, rather than treating whichever symptom is more noticeable and calling it done.
