The worse the sleep apnea, the greater the risk of heart attack and stroke

Obstructive sleep apnea does not raise cardiovascular risk in a straight line. Mayo Clinic’s overview of the condition states the relationship directly: the worse the obstructive sleep apnea, the greater the risk of coronary artery disease, heart attack, heart failure and stroke. The device most often prescribed to blunt that risk, continuous positive airway pressure, keeps the airway open by delivering pressurized air through a mask worn during sleep.

Many people with the condition develop high blood pressure long before anyone diagnoses the apnea behind it, and that persistent pressure surge is one of the clearest mechanical paths from disrupted breathing to lasting cardiovascular damage. Men are two to three times more likely than premenopausal women to have the condition, though the risk climbs for women after menopause.

The muscles supporting the tongue and soft palate relax and narrow or close the airway during sleep, lowering blood oxygen and raising carbon dioxide until the brain briefly rouses the sleeper to reopen it, a pattern that can repeat more than five times an hour without the person ever remembering waking. Excess weight, older age, a family history of the condition, enlarged tonsils, chronic nasal congestion and smoking all raise the odds of that obstruction happening in the first place.

A hypoxic-burden metric outperforms the apnea count

For decades, clinicians have graded obstructive sleep apnea mainly by counting how many times an hour the airway collapses, a tally called the apnea-hypopnea index. A study funded in part by the National Heart, Lung, and Blood Institute and published in the American Journal of Respiratory and Critical Care Medicine found a different number predicts heart trouble more reliably: how far, and for how long, blood oxygen actually falls during those collapses. Researchers reviewed data from more than 4,500 middle-aged and older adults enrolled in two long-running cohorts, tracking who went on to have a heart attack, stroke or cardiovascular death.

The pattern held in both cohorts, though the size of the effect differed sharply. In the more ethnically diverse Multi-Ethnic Study of Atherosclerosis, which followed 1,973 men and women with an average age of 67 for about seven years, every additional unit of that oxygen-drop measurement, called hypoxic burden, corresponded to a 45% higher risk of a primary cardiovascular event, while airway obstruction severity alone explained 38% of the observed risk. In the older, all-male Osteoporotic Fractures in Men Study, which followed 2,627 men with an average age of 76 for nine to 12 years, the same hypoxic-burden measure carried a 13% increased risk, with obstruction accounting for 12%.

The airway, not body weight, explains the oxygen drop

Gonzalo Labarca, an instructor in medicine at Brigham and Women’s Hospital and Harvard Medical School and a co-author of the study, said the hypoxic-burden measurement holds up even after accounting for factors that might otherwise explain it. “That’s something that makes this metric specific to sleep apnea,” Labarca said. “The connections are less explained by obesity or another factor.” The researchers traced a high hypoxic burden mainly to severe obstruction of the airway itself, not to abdominal weight or reduced lung capacity, a distinction that matters because excess weight is often treated as the primary driver of the condition.

Blood pressure, clotting and irregular heartbeat compound the damage

Sudden drops in blood oxygen during obstructive sleep apnea raise blood pressure and strain the cardiovascular system, according to Mayo Clinic, and the condition also increases the risk of arrhythmias, irregular heartbeats that can themselves affect blood pressure. Where underlying heart disease is already present, repeated arrhythmia episodes could lead to sudden death.

The same repeated oxygen drops raise the activity of clotting factors in the blood and produce inflammation, mechanisms that compound stroke risk independent of blood pressure alone. Sleep apnea has also been linked to a higher risk of severe COVID-19 and to eye conditions such as glaucoma, though those particular complications are considered treatable on their own.

Daytime drowsiness compounds the danger beyond the cardiovascular system. People with obstructive sleep apnea often experience severe fatigue, irritability and difficulty concentrating from a lack of restorative sleep, and excessive drowsiness raises the risk of falling asleep at work, while watching television or behind the wheel, putting affected people at higher risk of work-related and motor vehicle accidents.

Treatment brings measurable risk down

Obstructive sleep apnea is highly treatable, and breathing and sleep disruptions can be greatly reduced or eliminated with ongoing therapy. Continuous positive airway pressure remains the standard prescribed device, though a jaw-repositioning mouthpiece, surgery or, for people with obesity, weight loss can also improve symptoms depending on the underlying cause.

Ali Azarbarzin, director of the Sleep Apnea Health Outcomes Research Group at Brigham and Women’s Hospital and Harvard Medical School and the study’s senior author, said the findings will help doctors better characterize the highest-risk versions of the condition. “These findings will help better characterize high-risk versions of obstructive sleep apnea,” Azarbarzin said, adding that enrolling a higher-risk version of the condition in a randomized clinical trial could eventually show that treating sleep apnea helps prevent future cardiovascular events. Marishka K. Brown, director of the National Center for Sleep Disorders Research at the National Heart, Lung, and Blood Institute, said the newly identified mechanism could reshape how the condition is studied. “Understanding these mechanisms could change the way that sleep apnea clinical trials are designed and what is measured in clinical practice,” Brown said. Earlier research the NIH-funded team cited estimated that nearly 54 million people in the United States have obstructive sleep apnea, putting all of them at elevated cardiovascular risk to some degree.

Whether treating the highest hypoxic-burden patients specifically, rather than treating obstructive sleep apnea generally, actually lowers heart attack and stroke rates remains untested. Azarbarzin’s team has not yet enrolled patients in the randomized trial the findings are meant to support.

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This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.