Does Going to Bed at Different Times Increase Heart Disease Risk?

TL;DR

• A 2026 Finnish study followed 3,231 adults from the age of 46 for around a decade and recorded 128 major cardiovascular events.
• Among those spending less than the median time in bed, the most irregular bedtimes carried an adjusted hazard ratio of 2.01 against the most regular — but the confidence interval ran from 1.00 to 4.01, so the result sits on the edge of statistical significance.
• A far larger UK study of 72,269 adults found a more modest association, with a hazard ratio of 1.26 for the most irregular sleepers.
• Regularity and duration are different measurements. Averaging eight hours tells you nothing about whether those hours fall at the same time each night.
• These are observational studies. They cannot show that irregular bedtimes cause heart disease, or that making your bedtime consistent would prevent it.

Beyond How Long You Sleep

Sleep advice has traditionally been about quantity. Adults are told to aim for seven to nine hours, with some attention to quality and to disorders such as insomnia and sleep apnoea. That framing treats sleep as a single number.

Two people can both average eight hours and sleep very differently. One goes to bed at eleven and gets up at seven, most nights. The other alternates between early nights, late evenings and long weekend lie-ins. The average is identical; the pattern is not.

Researchers now separate sleep duration, sleep quality, sleep timing and sleep regularity, and treat them as distinct dimensions of sleep health. The American Heart Association's 2025 scientific statement on multidimensional sleep health took the same position, naming regularity and timing as relevant to cardiovascular health while calling for better causal evidence.

What the Finnish Study Found

The study, published in BMC Cardiovascular Disorders in 2026, drew on the Northern Finland Birth Cohort 1966. It included 3,231 participants who attended a health assessment around the age of 46 between 2012 and 2014, and who wore activity monitors for seven consecutive nights.

From those recordings the researchers calculated how much each person's bedtime, wake time and sleep midpoint varied from night to night, expressed as a standard deviation across the week, and sorted participants into three groups. They then linked the cohort to Finnish health registers and followed them until the end of 2023.

The outcome was a composite of major adverse cardiac events: heart attack, unstable angina, stroke, hospitalisation for heart failure and cardiovascular death. Over roughly ten years, 128 participants — 4% of the cohort — had one.

Participants were also split by whether they fell above or below the cohort median of seven hours and fifty-six minutes. Among the group below that median, the most irregular bedtimes carried an adjusted hazard ratio of 2.01 against the most regular, with a 95% confidence interval of 1.00 to 4.01 and a p-value of 0.049. Irregular sleep midpoints gave almost the same result: a hazard ratio of 2.00, confidence interval 1.01 to 3.98, p-value 0.048.

Those estimates were adjusted for sex, employment status, body mass index, systolic blood pressure, LDL cholesterol, glycated haemoglobin and physical activity. No equivalent association appeared among participants above the median, and irregular wake times showed no significant association at all.

> The study does not show that anyone with a variable bedtime has doubled their risk of heart disease. It identifies an association within one subgroup, with wide statistical uncertainty around it.

A Note on What Was Measured

One detail deserves care, because it changes what the finding means. The monitors recorded movement, and the University of Oulu describes the split as being by time in bed rather than time asleep — fewer than eight hours in bed, not fewer than eight hours of sleep. The paper itself sometimes uses the looser language of sleep duration.

That distinction is not pedantry. Lying in bed awake counts towards time in bed and not towards sleep, and for anyone with insomnia the gap between the two is the entire problem. A measure of time in bed will group a person who sleeps soundly for seven and a half hours together with someone who is in bed for seven and a half hours and asleep for five.

The practical consequence is that the subgroup where the association appeared is defined less precisely than a sleep-duration threshold would suggest. It is a reason to hold the finding loosely rather than to dismiss it.

What the Larger UK Research Shows

The Finnish result does not stand alone. A study in the Journal of Epidemiology & Community Health examined sleep regularity and cardiovascular events in 72,269 UK Biobank participants aged 40 to 79, who wore wrist accelerometers for a week. The researchers used the Sleep Regularity Index, which scores how consistently someone is asleep or awake at the same times on consecutive days.

Over around eight years, the most irregular sleepers had an adjusted hazard ratio of 1.26, with a 95% confidence interval of 1.16 to 1.37, against regular sleepers. Moderately irregular sleepers sat between the two.

That is a much narrower confidence interval than the Finnish estimate, built on more than twenty times as many people — but it also describes a far smaller effect. A 26% higher relative hazard is not the same claim as a doubling, and the gap between the two findings is as informative as either one alone.

The UK study also looked at whether getting enough sleep offset the association. Among moderately irregular sleepers, meeting age-specific duration recommendations was associated with no clear excess risk. Among the most irregular, an elevated association remained. That does not prove eight hours fails to protect the heart; it suggests average duration may not capture everything that matters. A further UK Biobank analysis, published in the Journal of the American Heart Association in 2025, found a similar pattern for night-to-night variation in how long people slept rather than when.

Why Timing Might Matter to the Heart

The most plausible explanation is circadian. The body runs an internal clock that coordinates sleep, hormone release, temperature, metabolism and cardiovascular function across roughly twenty-four hours, and blood pressure and heart rate both follow daily rhythms shaped by that clock and by light.

When sleep and waking move around from day to day, the timing of those behaviours falls out of step with the rhythms running underneath them. Researchers have proposed several routes by which repeated misalignment might affect the cardiovascular system, including blood pressure regulation, glucose handling, autonomic nervous system activity and inflammatory signalling.

A plausible mechanism is not proof. People whose sleep is irregular also differ in working hours, stress, income, diet, alcohol and underlying health. Some of those can be measured and adjusted for; others cannot be captured well enough to rule out. Shift workers in particular have irregular sleep because of their jobs, not their choices, and treating sleep timing as a lifestyle decision misses a large part of who is affected.

Does a Late Night or a Weekend Lie-In Matter?

The research does not support treating every departure from a usual bedtime as a threat. A late dinner, a long journey or an evening out is a different thing from a schedule that swings about all week, and nothing in these studies shows that a single late night does measurable cardiovascular harm.

Weekend catch-up sleep is the most awkward case. Someone sleeping longer on Saturday and Sunday is often making up a deficit accumulated during the week. Forcing an early alarm at weekends, without fixing the short nights that created the debt, would reduce the irregularity while making the underlying sleep loss worse.

People with insomnia should be especially careful with this material. Lying in bed at a fixed hour, awake and trying, is one of the things that maintains the problem. Behavioural treatment for insomnia puts its emphasis on a steady waking time and on not spending long stretches awake in bed — which is a different instruction from going to bed at the same time regardless of whether you feel sleepy. Our Complete Guide to Insomnia covers that distinction.

What the Research Cannot Tell Us

There are several reasons to resist turning the Finnish result into a claim that irregular bedtimes double your risk, and the first is that the number of events was modest. Only 128 occurred across the whole cohort, and the doubled estimates come from a subgroup within that. The confidence intervals run from roughly no increase at all up to around a fourfold one, which is a wide range to build advice on.

The main bedtime result was also only just significant, at a p-value of 0.049. That is a statement about how likely the data would be under chance, not a measure of how important the effect is, and it offers little protection against a chance finding among several analyses.

The cohort was homogeneous. All participants were the same age, drawn from one region of Finland, ethnically similar and mostly women — which limits how far the result travels. Sleep was measured across a single week, years before most events occurred, and nobody knows how stable those patterns were over the decade that followed.

It is also observational, so residual confounding and reverse causation remain live. The researchers did take one step against the latter, excluding anyone who had a cardiac event within two years of the baseline measurement, which makes it less likely that undiagnosed illness was disturbing their sleep at the point of recording.

Finally, a hazard ratio is not a personal probability. The cohort's 4% event rate cannot be doubled to produce an individual's risk, and nothing here supports a calculation of that kind.

What This Actually Means

Sleep health is not one number. Duration matters, and so do continuity, timing, regularity, how you function during the day and whether a sleep disorder is present. The case for regularity as one of those dimensions is now reasonably strong. The case that correcting it independently prevents cardiovascular events has not been made, and the two should not be confused.

For anyone whose schedule is their own to set, broadly consistent sleep and waking times are a sensible aim and cost nothing to try. Our Sleep Reset sets out how to go about it, including why the waking time is the part worth anchoring first.

What the evidence does not support is achieving consistency by cutting sleep short. Someone sleeping too little all week has not solved anything by becoming punctual about it, and neither this research nor the larger UK work establishes that regularity outranks duration in every situation.

Where schedules are not a matter of choice — shift work, caring, night feeds, insomnia — this evidence should not become another thing to feel responsible for. And for cardiovascular risk specifically, the established measures still do the heavy lifting: blood pressure, not smoking, physical activity, cholesterol and diabetes where relevant, and assessment for sleep apnoea where there are symptoms. A steadier bedtime may be a reasonable addition to that list. It is not a replacement for anything on it.

FAQ

Can irregular sleep cause heart disease?

Observational studies have found associations between irregular sleep and higher rates of cardiovascular events. They have not shown that irregular sleep causes them. Other health, behavioural and social factors may account for part or all of the link.

How much should my bedtime vary?

There is no validated threshold separating a healthy bedtime from a harmful one, and no point at which risk has been shown to start rising. The research supports a reasonably consistent routine rather than hitting an exact time.

Is eight hours at irregular times better or worse than seven hours consistently?

The studies do not answer that. Both duration and regularity appear to matter, and there is no evidence that trading one away for the other is a good idea.

Do weekend lie-ins increase heart attack risk?

Nothing in this research shows that. Longer weekend sleep often reflects a deficit built up during the week, and an occasional shift is not the same as a persistently unpredictable schedule.

Will making my bedtime more regular reduce my cardiovascular risk?

No trial has shown that changing sleep regularity independently prevents heart attacks or strokes. It is a reasonable general sleep habit, not a proven cardiovascular treatment.

The Bottom Line

A consistent bedtime is emerging as a plausible part of cardiovascular health, and the Finnish study adds to a growing body of work linking irregular sleep timing to serious outcomes.

But its most striking number came from a subgroup of a modest cohort, with a confidence interval touching 1.00 and a p-value of 0.049, in a population that was all one age and mostly women. The much larger UK study points to a real but considerably smaller association.

That is enough to take sleep regularity seriously. It is not enough to promise that a fixed bedtime will protect your heart. Protect your sleep opportunity, keep a routine you can sustain, and deal with the cardiovascular risk factors that already have evidence behind them. Consistency probably matters. Precision to the minute almost certainly does not.

This article is general information and not a substitute for medical advice. If you have concerns about your heart health or persistent problems with your sleep, speak to your GP.

Sources

• Nauha L, Niemelä M, Azadifar S, et al. Sleep timing irregularity in midlife: association with incident major adverse cardiac events and cardiovascular disease mortality over a 10-year follow-up. BMC Cardiovascular Disorders 2026;26:299. doi:10.1186/s12872-026-05762-4
• Chaput JP, Biswas RK, Ahmadi MN, et al. Sleep regularity and major adverse cardiovascular events: a device-based prospective study in 72,269 UK adults. Journal of Epidemiology & Community Health 2025;79:257-263. doi:10.1136/jech-2024-222795
• Huang T, Kianersi S, Wang H, et al. Sleep duration irregularity and risk for incident cardiovascular disease in the UK Biobank. Journal of the American Heart Association 2025;14:e040027. doi:10.1161/JAHA.124.040027
• St-Onge MP, Aggarwal B, Fernandez-Mendoza J, et al. Multidimensional sleep health: definitions and implications for cardiometabolic health. A scientific statement from the American Heart Association. Circulation: Cardiovascular Quality and Outcomes 2025;18:e000139.
• University of Oulu. Irregular bedtime linked to higher risk of cardiac events. 2026. oulu.fi