Summary: It’s not just how much you sleep, but when you go to bed that matters for your heart. A decadelong study revealed that inconsistent bedtimes in midlife can double the risk of major cardiovascular events, such as heart attacks or strokes.
The research tracked over 3,000 individuals and found that those with large “swings” in their nightly bedtime were at the highest risk—especially if they averaged less than eight hours of sleep. Interestingly, while irregular bedtimes were dangerous, irregular wake-up times showed no significant link to heart disease.
Key Facts
- The Double Risk Factor: Participants with irregular bedtimes who slept less than eight hours had twice the risk of myocardial infarction (heart attack) or cerebral infarction (stroke) compared to those with stable schedules.
- Bedtime vs. Wake-up Time: The study is the first to separate these variables. It found that the “anchor” for heart health is the time you go to sleep, not necessarily the time you wake up.
- Long-Term Tracking: Researchers followed a cohort of 3,231 people born in Northern Finland. Their sleep was monitored via activity trackers at age 46, and their health outcomes were followed for over 10 years using national registries.
- The “Midpoint” Metric: Variability in the “sleep midpoint” (the halfway point between falling asleep and waking up) was also strongly associated with higher cardiac risk.
Source: University of Oulu
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:
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.
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.
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.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our 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 reflects daily routines and lifestyle patterns, which influence cardiovascular health through circadian mechanisms that regulate cardiovascular processes. Wearable devices enable sensor-based assessment of sleep timing, offering insights into daily behavior. This cohort study examined how the regularity of wearable device–determined sleep timing (bedtime, wake-up time, and sleep midpoint) predicts incident major adverse cardiac event (MACE) and cardiovascular disease (CVD) mortality over a 10-year follow-up in midlife.
Methods
The study included 3,231 participants (39.5% men) from the Northern Finland Birth Cohort 1966 who attended the 46-year follow-up in 2012–2014. Participants were followed until December 31, 2023, or until a MACE (acute myocardial infarction, unstable angina, stroke, heart failure hospitalization, or CVD death) or were censored due to moving abroad or dying from a non-cardiovascular cause. Sleep timing regularity was assessed via 7-day standard deviation for bedtime, wake-up time, and sleep midpoint, categorized into tertiles: regular, fairly regular, and irregular. Cox proportional hazards models estimated hazard ratios (HRs) with 95% confidence intervals (CIs), adjusting for gender, employment status, body mass index, systolic blood pressure, glycated hemoglobin, low-density lipoprotein cholesterol, and total physical activity. Analyses were stratified by sleep duration below or above the group median (7 h 56 min).
Results
In total, 128 participants (4.0%) experienced MACEs during the follow-up period. Irregular sleep timing was associated with an elevated risk, but this association was observed only among participants whose sleep period was shorter than the group median. Individuals with irregular bedtimes had a 2.01-fold higher risk of MACEs compared to those with regular bedtimes (HR = 2.01, 95% CI: 1.00–4.01, p = 0.049), and those with irregular sleep midpoints had a 2.00-fold higher risk compared to those with regular midpoints (HR = 2.00, 95% CI: 1.01–3.98, p = 0.048).
Conclusions
Among the participants with sleep durations under eight hours, irregular sleep timing was a significant risk factor for MACEs. Specifically, variability in bedtime and sleep midpoint, but not in wake-up time, was associated with increased risk. These findings highlight the importance of consistent sleep behavior, particularly regular bedtimes, as a potential target for health promotion.
