Summary: It’s not only how long you sleep but also when you go to bed that matters for heart health. A decade-long follow-up found that irregular bedtimes in midlife are linked with a substantially higher risk of major cardiovascular events, including heart attack and stroke.
In a population-based study of 3,231 people, those with large swings in their nightly bedtime showed the greatest risk—particularly if their average time in bed was under eight hours. Notably, variability in wake-up times did not show a clear association with cardiovascular outcomes. These findings point to bedtime consistency as a potentially modifiable factor for cardiovascular prevention.
Key Facts
- Increased risk with irregular bedtimes: Participants who combined irregular bedtimes with less than eight hours in bed had about twice the risk of myocardial infarction or stroke compared with those who kept a regular sleep schedule.
- Bedtime, not wake time: The study separated bedtime, wake-up time and sleep midpoint and found bedtime variability to be the primary predictor of risk.
- Large cohort and long follow-up: Researchers followed 3,231 individuals born in Northern Finland, measured sleep using activity monitors at age 46, and tracked health outcomes for more than ten years through national health registers.
- Sleep midpoint matters too: Greater variability in the sleep midpoint (the halfway point between falling asleep and waking) was also associated with higher cardiovascular risk.
Source: University of Oulu
A new study from the University of Oulu indicates that pronounced shifts in bedtime during midlife may double the risk of serious cardiac events for people who sleep fewer than eight hours nightly. Using wearable activity monitors to estimate sleep timing and duration, researchers examined how regularity of bedtime, wake-up time and sleep midpoint related to major adverse cardiac events (MACE) over a follow-up period exceeding ten years.
The analysis found that individuals with the most irregular bedtimes and shorter sleep durations had the highest incidence of MACE. By contrast, variability in wake-up time was not clearly linked to increased cardiac risk. Major adverse cardiac events in the study included acute myocardial infarction, unstable angina, stroke, heart failure hospitalization and cardiovascular death—events identified through comprehensive healthcare registers.
“This is the first large cohort study to evaluate bedtime, wake-up time and sleep midpoint separately and to show that bedtime variability stands out as a key factor associated with cardiac risk,” says postdoctoral researcher Laura Nauha from the University of Oulu. Sleep timing and duration were measured with wrist-worn activity trackers that estimated participants’ time in bed over a seven-day period.
Nauha notes that bedtime regularity likely reflects the overall stability of daily routines and circadian alignment. “When bedtimes swing by hours from night to night, the body’s internal clocks—including those that regulate heart rate and blood pressure—are repeatedly shifted. Over time, that misalignment may contribute to chronic inflammation and vascular stress,” she explains.
The cohort consisted of individuals born in Northern Finland in 1966 who participated in the 46-year follow-up in 2012–2014. Their sleep was recorded for one week at age 46, and health outcomes were monitored through December 31, 2023. The study adjusted for established cardiovascular risk factors such as sex, employment status, body mass index, systolic blood pressure, glycated hemoglobin, LDL cholesterol and overall physical activity.
Key Questions Answered
A: Yes. The study found that bedtime regularity was the main driver of risk. Even with a consistent wake-up time, large swings in when you go to bed appear to disrupt circadian processes in a way that increases cardiovascular strain.
A: The greatest increase in risk was observed among those sleeping less than eight hours. For people with shorter sleep, maintaining a consistent bedtime seemed especially important and acted as a risk “multiplier” when combined with irregular timing.
A: Shifting bedtimes creates circadian misalignment. Key cardiovascular functions—heart rate, blood pressure and vascular tone—follow circadian rhythms; repeated changes in sleep timing force these systems to re-adjust, potentially promoting chronic inflammation and arterial stress over time.
Editorial Notes
- This article was edited by a Neuroscience News editor.
- The original journal paper was reviewed in full.
- Context and clarifications were added by editorial staff.
About this sleep and neurology research news
Author: Meri Rova
Source: University of Oulu
Contact: Meri Rova – University of Oulu
Image: The image is credited to Neuroscience News
Original Research: Closed access. “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 & Vahid Farrahi. BMC Cardiovascular Disorders. DOI: 10.1186/s12872-026-05762-4
Abstract
Sleep timing irregularity in midlife: association with incident major adverse cardiac events and cardiovascular disease mortality over a 10-year follow-up
Background
Sleep timing mirrors daily routines and lifestyle habits that influence cardiovascular physiology through circadian mechanisms. Wearable devices provide objective measurements of sleep timing, helping to assess how routine variability affects long-term heart health. This cohort study evaluated whether regularity of bedtime, wake-up time and sleep midpoint—as measured by activity trackers—predicts incident major adverse cardiac events (MACE) and cardiovascular mortality over ten years in midlife.
Methods
The analysis included 3,231 participants (39.5% men) from the Northern Finland Birth Cohort 1966 who attended a clinical follow-up at age 46 during 2012–2014. Sleep timing was captured over seven days and summarized as the standard deviation for bedtime, wake-up time and sleep midpoint, then categorized into tertiles (regular, fairly regular, irregular). Participants were followed until December 31, 2023, for occurrence of MACE (acute myocardial infarction, unstable angina, stroke, heart failure hospitalization, or cardiovascular death). Cox proportional hazards models estimated hazard ratios with adjustments for sex, employment, BMI, systolic blood pressure, glycated hemoglobin, LDL cholesterol and total physical activity. Analyses were stratified by sleep duration above or below the cohort median (7 h 56 min).
Results
During follow-up, 128 participants (4.0%) experienced a MACE. Irregular sleep timing was associated with higher risk, but this effect was limited to participants whose sleep duration was shorter than the group median. Compared with regular bedtimes, irregular bedtimes were linked to a twofold higher risk of MACE (HR = 2.01, 95% CI: 1.00–4.01, p = 0.049). Similarly, irregular sleep midpoints were associated with a twofold higher risk (HR = 2.00, 95% CI: 1.01–3.98, p = 0.048). Variability in wake-up time did not show a significant association.
Conclusions
For midlife adults with shorter sleep durations, inconsistent sleep timing—especially irregular bedtimes and sleep midpoints—was associated with higher incidence of major adverse cardiac events. These results underscore the potential importance of maintaining a consistent bedtime as a practical, modifiable behavior for cardiovascular health promotion.