Irregular bedtimes in middle age may double risk of serious heart disease

A study by the University of Oulu has found that middle-aged adults with inconsistent bedtimes face twice the risk of severe cardiovascular disease, particularly if they sleep less than eight hours per night.

The research, published by Finnish public broadcaster Yle, suggests that large variations in bedtime significantly increase the risk of heart and vascular conditions. The effect was most pronounced among those with shorter sleep durations.

Dr. Laura Nauha, a postdoctoral researcher at the University of Oulu, explained that the body’s circadian rhythm—operating on a roughly 24-hour cycle—benefits from consistent sleep patterns. “If a person supports this rhythm through their behaviour, it is likely best for their health and performance,” she said.

While the study did not define exact thresholds for harmful bedtime variation, Nauha noted that regular sleepers typically had fluctuations of about an hour, whereas irregular sleepers varied far more. Previous research has linked inconsistent sleep schedules to cardiovascular risks, but this study is the first to isolate the impact of bedtime irregularity specifically.

The findings also emphasised the importance of maintaining a steady sleep schedule even on weekends and holidays. Nauha advised against excessive flexibility, though she acknowledged some adaptability can be beneficial. She criticised daylight saving time changes, stating that no circadian rhythm researcher supports forced clock adjustments due to their strain on the body.

The study tracked over 3,000 individuals born in Northern Finland in 1966, monitoring their sleep patterns via activity trackers at age 46. Participants were followed for more than a decade using healthcare registry data.

Unlike bedtime irregularity, variations in wake-up times showed no clear link to cardiovascular disease in the study.