Heart Attack and Stroke: Irregular Sleep Schedule Doubles The Risk

This study analyzed how the regularity of sleep schedules influences the risk of cardiovascular disease over ten years. Using wearable devices to monitor the sleep of more than three thousand adults, researchers observed that people with irregular sleep schedules had a higher risk of serious cardiac events, especially when they slept less than eight hours a night. The results highlight that maintaining consistent sleep schedules can be as important as getting enough sleep to protect heart health.

Sleep is an essential part of human life, not only for rest but also for maintaining the overall health of the body. In recent years, researchers have realized that it is not only the number of hours slept that matters, but also the regularity of sleep and wake times.

Our body functions based on an internal "biological clock," which regulates important processes such as blood pressure, heart rate, and metabolism. When this natural rhythm is constantly altered, as happens with irregular sleep schedules, it can negatively affect heart health over time.

With the advancement of technology, wearable devices, such as smartwatches and monitoring bracelets, have made it possible to track sleep habits in detail throughout the day. These devices can automatically record when a person sleeps and wakes up, offering more accurate data on sleep patterns over several days.

Taking advantage of this technology, the study sought to understand whether the regularity of sleep schedules could predict the risk of cardiovascular problems over many years.

To investigate this question, researchers used data from a large group of people who have been part of a population study conducted in Finland since birth. At the time analyzed, the participants were around forty-six years old, a stage of life in which cardiovascular risks begin to become more relevant.

In total, more than three thousand people participated in the analysis, being followed for approximately a decade to verify the emergence of heart problems or heart-related death.

The methodological part of the study was carefully planned to accurately capture sleep habits. Over a period of seven days, participants used devices that automatically recorded their sleep and wake times. From this data, the researchers calculated how much these times varied throughout the week.

In simple terms, they measured whether the person always slept and woke up at similar times or if there were large differences from one day to the next. Based on this, participants were classified into three groups: those with regular, moderately regular, and irregular schedules.

In addition to observing sleep, the researchers also monitored the participants' health over time. They recorded the occurrence of major cardiovascular events, such as heart attack, stroke, heart failure, or heart-related death.

They also considered other factors that could influence the results, such as body weight, blood pressure, blood sugar levels, cholesterol, physical activity, and employment status. This was important to ensure that the observed effects were truly related to sleep patterns, and not to other aspects of health or lifestyle.

To analyze the data, a statistical method was used that allows estimating the risk of an event occurring over time, taking into account multiple variables simultaneously. Researchers also divided participants into two groups based on sleep duration: those who slept less than about eight hours per night and those who slept more. This division helped to understand whether sleep regularity would have different impacts depending on the number of hours slept.

The results showed that people with more irregular sleep schedules, especially in bedtime and midpoint of sleep (i.e., the central time between sleeping and waking), had approximately twice the risk of developing cardiovascular problems compared to those who maintained regular schedules.

This effect was particularly evident among individuals who slept less than eight hours per night. Interestingly, variation in wake-up time did not have as strong an association as variation in bedtime.

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Sleep timing irregularity in midlife: association with incident major adverse cardiac events and cardiovascular disease mortality over a 10-year follow-up

Laura Nauha, Maisa Niemelä, Saeid Azadifar, Raija Korpelainen, and Vahid Farrahi

BMC Cardiovascular Disorders. 24 March 2026

DOI: 10.1186/s12872-026-05762-4

Abstract:

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. 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). 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). 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.