Researchers at Flinders University in Australia tracked more than 3,000 adults with under-mattress sleep sensors over six months and found that people whose obstructive sleep apnea swings sharply from night to night were about 30% more likely to have suffered a heart attack, stroke, or heart failure.
The link held up even after accounting for how severe their apnea was on average.
The study, published in the journal SLEEP in 2026, suggests that the standard clinical practice of diagnosing sleep apnea with a single overnight lab test can overlook a distinct cardiovascular risk pattern.
What matters, the analysis indicates, is not only how bad a person's breathing pauses are on an average night, but how much that severity fluctuates from one night to the next.
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What night-to-night variability means
Obstructive sleep apnea is measured by the apnea-hypopnea index, or AHI, which counts breathing pauses per hour of sleep. Because a full overnight polysomnography is expensive and uncomfortable, most patients are diagnosed and categorized on the basis of a single night.
The Flinders team, led by Dr Bastien Lechat and Professor Danny Eckert of the Flinders Health and Medical Research Institute Sleep Health program, used data from consumers who had purchased an FDA-cleared under-mattress sensor.
Multi-night AHI values were collected for six months, and the researchers calculated how much each person's nightly score varied.
Comparing the top quarter of variability against the bottom quarter, night-to-night swings were associated with 34% higher odds of a major cardiovascular or cerebrovascular event, independent of average apnea severity, age, sex, body mass index, alcohol, and smoking.
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Why a single test may miss it
The Flinders group notes that up to 50% of people can slip into a different apnea severity category from one night to another, and around 20% may be misclassified by conventional single-night testing. To get a stable estimate of severity, the paper says a minimum of 14 nights of monitoring is needed.
"Many people assume sleep apnoea is stable, but the reality is very different, and some nights can be much worse than others, and this repeated up and down strain may place extra stress on the heart," Dr Lechat said in a Flinders University release.
He added a warning about apparently mild cases. "A single night sleep test may falsely reassure some patients, because people with mild average sleep apnoea can still be at higher risk if their breathing problems swing dramatically between nights."
Professor Eckert framed the biological plausibility. "The body may struggle to adapt to repeated changes in oxygen levels and sleep disruption," he said, adding that the repeated swings from night to night can quietly stress the heart and blood vessels over time.
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What it means in practice
The study is observational and cross-sectional, so it cannot prove that variable apnea causes cardiovascular events, only that the two travel together in this sample.
Cardiovascular outcomes were self-reported, and the group skewed male, younger, and more affluent than the general population. The authors call for prospective trials to test the mechanism directly.
Even so, sleep apnea is a major public health problem. The American Academy of Sleep Medicine estimates that at least 25 million U.S. adults live with obstructive sleep apnea, and the condition is linked to high blood pressure, heart disease, type 2 diabetes, stroke, and depression.
For readers who already snore, wake unrefreshed, or have been told they stop breathing at night, the takeaway is simple. A one-off sleep test is a starting point, not a verdict.
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Anyone worried about symptoms or an existing diagnosis should raise the question of longer-term monitoring with their doctor, particularly if there are other cardiovascular risk factors in play.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.