Sleep patterns that vary significantly from night to night may pose hidden dangers to heart health, according to new research from Flinders University. A recent study published in the journal SLEEP reveals that individuals with fluctuating severity in obstructive sleep apnea (OSA) are 30% more likely to experience cardiovascular events such as heart attacks, strokes, or heart failure.
The findings highlight that variability in sleep apnea severity can be as critical as the average severity of the condition. Obstructive sleep apnea, a common sleep disorder, causes repeated interruptions in breathing during the night and is known to affect millions of people globally. While it is often linked to loud snoring, restless nights, and daytime fatigue, its connection to serious heart risks is becoming increasingly clear.
Night-to-Night Variability: A Hidden Risk
The study analyzed over 3,000 adults who monitored their sleep using under-mattress sensors at home over several months. Researchers discovered that individuals with significant night-to-night fluctuations in their breathing patterns were about one-third more likely to report cardiovascular conditions compared to those with consistent sleep patterns.
"Many people assume sleep apnea 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", explained Dr. Bastien Lechat, lead author of the study and expert at the Flinders Health and Medical Research Institute (FHMRI) Sleep Health.
Dr. Lechat also emphasized that the common practice of assessing sleep apnea through a single-night test might not capture the full picture for individuals whose symptoms vary significantly. "A single night sleep test may falsely reassure some patients, because people with mild average sleep apnea can still be at higher risk if their breathing problems swing dramatically between nights", he said.
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Widening the Lens on Cardiovascular Risk
The study’s senior author, Professor Danny Eckert, Director of FHMRI Sleep Health, echoed these concerns, stating that the body might struggle to adapt to frequent oxygen level changes and sleep disruptions. "The body may struggle to adapt to repeated changes in oxygen levels and sleep disruption. These night-to-night swings can quietly stress the heart and blood vessels over time without being picked up by standard testing", said Professor Eckert.
Support for these findings came from a second international study, also led by Flinders researchers and published in npj Digital Medicine. This study tracked nearly 30,000 people over several years using home-based digital health devices. The results showed that severe sleep apnea, high night-to-night variability, and even regular snoring were all linked to faster aging of blood vessels - a significant early warning sign for cardiovascular disease.
Dr. Lucia Pinilla, lead author of the second study, pointed out the risks for individuals with mild sleep apnea but high variability. She explained that this group exhibited vascular health similar to those with severe sleep apnea, identifying a previously overlooked population at risk. "These findings show that one-night tests can miss people at real risk", said Dr. Pinilla. "Sleep should be seen as a moving picture rather than a single photograph, and understanding nightly patterns can help doctors better identify who needs early intervention."
New Approaches to Sleep Monitoring
The studies underscore the importance of multi-night monitoring to understand sleep apnea severity fully. Professor Eckert compared the approach to how other chronic conditions are managed: "Blood pressure and blood sugar are measured repeatedly over time, and sleep health should be treated the same way."
The growing availability of home-based health technologies offers a promising solution for tracking sleep over extended periods, allowing for more accurate assessments in real-world conditions. However, the researchers emphasized that these studies do not definitively prove that sleep apnea variability causes heart disease. Instead, they underline the need for further long-term research and a shift in how sleep apnea is evaluated.
"If you snore or feel unrefreshed after sleep, speaking with a health professional could help uncover hidden risks to your heart and there are many options available for treatment", said Dr. Lechat.
With heart disease remaining the leading cause of death worldwide, identifying and mitigating these risks early could be a critical step toward improving public health outcomes. The research urges a reevaluation of current diagnostic practices to better capture the nuanced relationship between sleep and cardiovascular health.
