Going to bed at irregular times, not just too late, may be quietly putting your heart at risk. Researchers who tracked more than 3,000 Finnish adults for a decade found that people with the most inconsistent bedtimes were about twice as likely to suffer a serious cardiac event as those who turned in at roughly the same hour each night.
The finding comes from a study published in March 2026 in BMC Cardiovascular Disorders, drawing on 3,231 middle-aged participants from the Northern Finland Birth Cohort 1966. Sleep was measured with wrist activity trackers over 14 consecutive days, and participants were followed for about 10 years for any first heart attack, stroke, unstable angina, heart failure hospitalization, or cardiovascular death.
The doubled risk was not spread evenly across the group. It showed up almost entirely in people who slept less than the median of about 7 hours 56 minutes a night, where an irregular bedtime carried a hazard ratio of 2.01 (95% CI 1.00-4.01). Among those sleeping longer, no similar link appeared.
Wake-up time did not carry the same signal
The researchers looked separately at three things: when people went to bed, when they got up, and the midpoint of the sleep window. Irregular bedtimes and irregular sleep midpoints were both tied to elevated cardiac risk in shorter sleepers. Irregular wake-up times were not.
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That distinction is the practical heart of the paper. Wake-up time is often dictated by work, school runs, or an alarm clock. Bedtime is usually the more flexible end, and it is the end the study flags as the one worth anchoring.
"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," said Laura Nauha, postdoctoral researcher at the University of Oulu, in a statement from the university.
How big the swings were
To sort the participants, the researchers grouped them into thirds based on how much their bedtime varied from night to night. In the most regular group, bedtimes drifted by only about 33 minutes on average. In the most irregular group, the swing was closer to 108 minutes, more than an hour and a half between an early night and a late one.
Over the roughly 10-year follow-up, 128 participants, about 4 percent, had a first major cardiac event. The absolute rate is modest, but the doubling of risk in short sleepers with erratic bedtimes stood up after the researchers adjusted for standard cardiovascular factors.
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This is an observational study, so it can show association rather than prove cause. Still, it lines up with earlier work suggesting that a steady bedtime is linked to a substantially lower risk of dying early, and it adds a specific heart outcome to that picture.
What it means in practice
For anyone already sleeping around eight hours, the study did not find an extra penalty for a variable schedule. For the very common situation of getting less than that, the takeaway is narrower and more useful than a generic push for more sleep. Anchor the time you get into bed first, even before you focus on the total.
That means picking a bedtime you can hit on most weeknights, protecting it from late scrolling or a delayed dinner, and accepting that the alarm on the other end may be the least movable part of the day. It is, as Nauha put it in the university's statement, "one factor that most of us can influence."
People with existing heart conditions, chronic insomnia, or symptoms such as chest pain, breathlessness, or unexplained fatigue should still bring those concerns to their own doctor rather than treat sleep timing as a stand-alone fix. But for a healthy adult trying to protect a healthy heart, the message from this Finnish cohort is unusually concrete. The clock at bedtime may matter as much as the number of hours that follow.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.