A decade-long study has found that inconsistent bedtimes combined with insufficient sleep may significantly raise the risk of serious cardiovascular events, including heart attack and stroke.
Researchers report that adults who both slept less than eight hours per night and maintained irregular sleep schedules faced nearly double the risk of major cardiovascular events compared with those who kept more consistent routines.
The findings come from scientists at the University of Oulu, whose research was published in the BMC Cardiovascular Disorders.
The study analyzed long-term health outcomes in middle-aged adults and adds to growing evidence that sleep consistency, not just duration, plays a critical role in heart health.
To explore the relationship, researchers used data from 3,231 participants in the Northern Finland Birth Cohort 1966.
Participants wore wrist-based activity monitors for up to two weeks, allowing scientists to track sleep timing, duration, bedtimes, wake-up times, and sleep midpoint, the halfway point between falling asleep and waking.
The researchers then analyzed seven consecutive nights of sleep data and followed participantsβ health records for the next 10 years.
During the follow-up period, investigators tracked major cardiovascular events such as heart attack, stroke, and cardiovascular-related deaths.
Sleep patterns were categorized as regular, fairly regular, or irregular.
Participants also completed questionnaires covering lifestyle factors including smoking and alcohol use, and underwent clinical assessments for blood pressure, cholesterol, body mass index, and blood glucose levels.
The results revealed a striking pattern: individuals with both irregular bedtimes and fewer than eight hours of sleep per night had nearly double the risk of experiencing a major cardiovascular event.
A similar increase in risk was observed among those with highly irregular sleep midpoints, suggesting that disruptions to circadian rhythm stability may be particularly harmful.
However, irregular wake-up times alone were not significantly linked to increased risk.
Health experts say the findings highlight how sleep timing influences biological systems that regulate cardiovascular health.
The Centers for Disease Control and Prevention recommends adults get at least seven hours of sleep nightly, yet roughly one-third of adults fail to meet that threshold.
Insufficient or inconsistent sleep can disrupt circadian rhythms that regulate blood pressure, heart rate, and hormone release.
When sleep is irregular, blood pressure may remain elevated overnight instead of dipping during rest, placing added strain on the cardiovascular system.
Sarathi Bhattacharyya, who was not involved in the study, emphasized that circadian disruption affects the bodyβs recovery processes.
He explained that chronic sleep deprivation can elevate stress hormones and interfere with hormone signaling, both of which contribute to increased cardiovascular risk.
Similarly, Brian Zachariah described the results as clinically meaningful, noting that the observed hazard ratio of roughly two is comparable to traditional cardiovascular risk factors.
He highlighted that irregular bedtimes, rather than wake-up times, appeared to drive the increased risk, suggesting that bedtime variability may reflect broader behavioral instability and circadian disruption.
According to Zachariah, inconsistent sleep timing can promote insulin resistance, systemic inflammation, and metabolic dysregulation, all of which are linked to atherosclerosis and thrombosis.
Cardiology experts say the findings reinforce the growing understanding that sleep quality encompasses more than total hours.
Cheng-Han Chen noted that circadian rhythm disruptions can cause fluctuations in cortisol and adrenaline levels, contributing to higher blood pressure and obesity.
He added that since heart disease remains the leading cause of death in the United States, a two-fold increase in cardiovascular risk represents a meaningful public health concern.
Researchers conclude that maintaining a consistent sleep schedule may be as important as achieving adequate sleep duration.
They suggest that public health guidance should emphasize regular bedtimes alongside recommendations for sufficient sleep.
The studyβs long follow-up period strengthens the evidence that sleep irregularity can have lasting consequences for cardiovascular health.
While further research is needed to determine whether improving sleep consistency reduces risk, the findings suggest that simple behavioral changes, such as going to bed at the same time each night and aiming for at least seven to eight hours of sleep, may play a meaningful role in protecting heart health.
