BMC study links irregular sleep

Laura Nauha and colleagues reported in BMC Cardiovascular Disorders on March 24 that irregular sleep timing in midlife was linked to a higher risk of major cardiovascular events over about a decade of follow-up. The cohort study analyzed 3,231 participants in the Northern Finland Birth Cohort 1966, using wearable-device data collected in 2012 to 2014 and health outcomes tracked through December 31, 2023. The association appeared only among participants whose sleep period was shorter than the group median of 7 hours 56 minutes, according to the paper. The University of Oulu, where Nauha is a postdoctoral researcher, said in a March 30 research summary that irregular bedtimes and shifting sleep midpoints were the main signals, while irregular wake-up times showed no clear link. ### Which sleep pattern did the study single out? The study measured three parts of sleep timing over seven consecutive days: bedtime, wake-up time and the midpoint between the two. Researchers then grouped participants by how regular or irregular those times were, based on variation recorded by activity monitors. Laura Nauha said in the University of Oulu summary that this was the first time the researchers had looked separately at variability in bedtime, wake-up time and sleep midpoint, and their independent links with major cardiac events. (oulurepo.oulu.fi) The paper’s abstract said bedtime and sleep midpoint irregularity, not wake-up time irregularity, were associated with higher risk in the shorter-sleep group. ### How large was the risk in the group sleeping less than eight hours? The BMC paper set the split at the cohort median sleep period of 7 hours 56 minutes. Among participants below that level, those with irregular bedtimes had a hazard ratio of 2.01 for major adverse cardiac events compared with those with regular bedtimes, while those with irregular sleep midpoints had a hazard ratio of 2.00, according to summaries of the study. (oulu.fi) The University of Oulu said the risk in that group was “roughly twice” that of people with more regular sleep patterns. The study recorded 128 major adverse cardiac events, or 4.0% of the cohort, during follow-up. ### Who was studied, and for how long? The participants came from the Northern Finland Birth Cohort 1966, a long-running population study. The BMC paper said 3,231 people attended the cohort’s age-46 follow-up in 2012 to 2014, and 39.5% were men. (drugs.com) The follow-up ran until December 31, 2023, or until a participant had a major adverse cardiac event, died from a non-cardiovascular cause, or moved abroad. (oulu.fi) The study defined those events as acute myocardial infarction, unstable angina, stroke, heart failure hospitalization, or cardiovascular death. ### What did outside coverage add? Daily Record and Cambridgeshire Live articles published on May 15 and May 16, respectively, cited the BMC paper and highlighted comments from neurologist Dr. (oulurepo.oulu.fi) Baibing Chen about the health effects of inconsistent sleep schedules, according to search results and syndicated versions of the reports. Those articles were not the primary source for the findings; the underlying study was published online on March 24 in BMC Cardiovascular Disorders. The University of Oulu summary did not frame the findings as proof that irregular sleep causes heart disease. The paper described the work as a cohort study and reported associations after adjusting for factors including gender, employment status, body mass index, systolic blood pressure, glycated hemoglobin, low-density lipoprotein cholesterol and total physical activity. (msn.com) ### Where can readers find the original study? BMC Cardiovascular Disorders published the paper as volume 26, article 299, with the title “Sleep timing irregularity in midlife: association with incident major adverse cardiac events and cardiovascular disease mortality over a 10-year follow-up.” The corresponding author listed in the paper is Vahid Farrahi. (oulurepo.oulu.fi) The University of Oulu posted its research summary on March 30, 2026, naming Laura Nauha as the study’s lead researcher in the public-facing release. Readers looking for the original methods and results can find the full paper through BMC Cardiovascular Disorders and the University of Oulu repository. (oulu.fi) (oulurepo.oulu.fi)