Well over 70 million Americans use digital activity trackers to track their sleep, steps, and heart rate. According to a new study, these everyday devices may also detect hidden threats to heart health, particularly when sleep times fluctuate during the night. 

Researchers at Scripps Research examined long-term data from wearable trackers and discovered a substantial correlation between irregular sleep habits and an increased risk of obstructive sleep apnoea and high blood pressure. The findings, published on December 3, 2025, in the Journal of Medical Internet Research, add to mounting evidence that how frequently people sleep may be as important as how long they sleep. 

The study concentrated on sleep variability, or the hour-by-hour differences in when a person falls asleep and wakes up. According to the study, individuals whose bedtimes fluctuated by only one hour from night to night had a more than doubled chance of sleep apnoea. They were also 71% more likely to have hypertension, which is a leading cause of heart attacks and heart failure. 

Sleep apnoea affects around 50 million Americans and is linked to an increased risk of abnormal heart rhythms, stroke, and heart disease. High blood pressure, which affects roughly half of all adults, usually develops quietly. Wearables can detect early warning signs, allowing people to seek medical attention before major damage occurs. 

The study used data from the REFRESH project, a smartphone-based sleep study involving over 1,000 adults in the United States. Nearly 400 people submitted an average of two years of sleep data from their trackers and filled out health evaluations. Most participants wore Fitbit devices, which allowed researchers to investigate long-term patterns rather than single nights. 

Experts believe that the strength of digital trackers is their capacity to collect continuous data across months and years. While the study found associations rather than causes, irregular sleep is known to affect stress hormones, inflammation, and metabolism, all of which are associated with cardiovascular disease. 

Wearables should not be used instead of medical tests, according to clinicians. However, they may prove valuable in highlighting hazardous tendencies and encouraging prompt check-ups. As researchers progress from pattern identification to prevention, one message is clear: maintaining a regular sleep schedule may be a simple yet effective step towards heart health.