An irregular bedtime in midlife may signal an increased risk of cardiovascular disease. A new study from the University of Oulu suggests that large swings in when people go to bed could double the risk of serious cardiac events — particularly among those who get less than eight hours of sleep.
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."
Key Questions Answered:
Q: If I wake up at the same time every day, does it matter if my bedtime varies?
A: According to lead researcher Laura Nauha, yes — it matters significantly. The study found that bedtime regularity was the primary driver of heart risk. Even if your wake-up time is consistent, swinging your bedtime by several hours disrupts your body's internal rhythms in a way that appears specifically taxing to the cardiovascular system.
Q: Is "eight hours" the magic number to protect the heart?
A: The risk was most pronounced in people getting less than eight hours of sleep. For those who already have shorter sleep durations, adding an irregular schedule acts like a "multiplier" for heart stress. If you can't get a full eight hours, keeping your bedtime consistent becomes even more vital for protection.
Q: Why does a shifting bedtime hurt the heart specifically?
A: Irregular bedtimes reflect a lack of "circadian alignment." Your heart rate, blood pressure, and vascular tone all follow a strict 24-hour clock. When you go to bed at different times, you force your heart to adjust to a shifting biological "start time," which can lead to chronic inflammation and arterial stress over time.