Irregular bedtime linked to higher risk of cardiac events

The researchers found that inconsistent bedtimes and greater variability in sleep timing were strongly associated with a higher risk of major cardiovascular events, especially when measured time in bed fell below eight hours. In this group, the risk was roughly twice that of people with more regular sleep patterns. By contrast, irregular wake-up times showed no clear link to cardiac events. In the study, major cardiovascular events were defined as conditions requiring specialised medical care, such as myocardial infarction or cerebral infarction.

“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.

Sleep duration and timing were estimated using activity monitors that tracked participants’ time 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.

The study followed 3,231 individuals born in Northern Finland in 1966. Their sleep patterns were recorded over one week at age 46, and their health outcomes were tracked for more than a decade using healthcare register data.

According to Nauha, many aspects of heart health are shaped by everyday habits. “Maintaining a regular sleep schedule is one factor that most of us can influence.”

Research article: Nauha, L., Niemelä, M., Azadifar, S. et al. Sleep timing irregularity in midlife: association with incident major adverse cardiac events and cardiovascular disease mortality over a 10-year follow-up. BMC Cardiovasc Disord (2026).