A growing body of evidence suggests that how consistently we sleep may matter just as much as how long we sleep.
Going to bed at inconsistent times in midlife may be linked to a higher risk of cardiovascular disease. A study from the University of Oulu found that large variations in bedtime could double the likelihood of serious cardiac events, especially among people who sleep less than eight hours per night.
The researchers reported that irregular bedtimes and greater variation in sleep timing were strongly connected to an increased risk of major cardiovascular events. This link was most evident in participants whose time in bed was under eight hours, where the risk was about twice as high compared with those who followed more consistent sleep schedules.
In contrast, inconsistent wake-up times did not show a clear association with cardiac risk. Major cardiovascular events in the study referred to conditions requiring specialized medical care, such as myocardial infarction or cerebral infarction.
What Makes This Study Different
“Previous research has linked irregular sleep patterns to heart health risks, but this is the first time we’ve looked separately at variability in bedtime, wake-up time and the midpoint of the sleep period—and their independent associations with major cardiac events,” says postdoctoral researcher Laura Nauha from the University of Oulu.
Researchers estimated sleep duration and timing using activity monitors that recorded how long participants spent in bed.
“Our findings suggest that the regularity of bedtime, in particular, may be important for heart health. It reflects the rhythms of everyday life—and how much they fluctuate,” Nauha says.
Long-Term Study Insights
The study tracked 3,231 individuals born in Northern Finland in 1966. Their sleep patterns were measured over one week at age 46, and their health outcomes were followed for more than a decade using healthcare registry data.
Nauha notes that many factors influencing heart health are tied to daily habits. “Maintaining a regular sleep schedule is one factor that most of us can influence.”
Reference: “Sleep timing irregularity in midlife: association with incident major adverse cardiac events and cardiovascular disease mortality over a 10-year follow-up” by Laura Nauha, Maisa Niemelä, Saeid Azadifar, Raija Korpelainen and Vahid Farrahi, 24 March 2026, BMC Cardiovascular Disorders.
DOI: 10.1186/s12872-026-05762-4
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