Daylight saving time does not increase heart attack risk, study shows

By Vijay Kumar MalesuReviewed by Susha Cheriyedath, M.Sc.Sep 10 2025

Researchers report that springing forward or falling back does not lead to spikes in heart attacks, easing concerns for patients and health systems alike.

Study: Daylight Savings Time and Acute Myocardial Infarction. Image Credit: Stokkete / Shutterstock

In a recent study published in the JAMA Network Open, researchers in the United States examined whether daylight saving time (DST) transitions affect the incidence of acute myocardial infarction (AMI) and in-hospital outcomes by comparing the weeks before, during, and after spring and fall clock changes, and estimated adjusted effects using a national registry.

Background

Each spring and fall, millions misplace an hour, and wonder if hearts pay the price. DST can disturb sleep and circadian rhythm, which are potential triggers for AMI. Early studies suggested brief spikes in AMI after the “spring forward,” prompting headlines and bills to end clock changes. Yet cardiovascular care and work patterns have evolved. Knowing whether today’s transitions matter can shape patient advice, staffing, and public policy. The answer affects sleep habits, shift work, and anxiety around time changes. The authors note that earlier positive signals may reflect underpowered designs and pre-pandemic practice patterns. Further research is needed to clarify real-world risks across seasons, regions, systems, and diverse populations.

About the study

This cross-sectional analysis utilized the American College of Cardiology (ACC) National Cardiovascular Data Registry (NCDR) Chest Pain-Myocardial Infarction (MI) Registry to compare patterns one week before, during, and one week after DST in spring and fall across the United States (US) from 2013 to 2022. Unique consecutive patients with ST-elevation myocardial infarction (STEMI) or non-ST-elevation myocardial infarction (NSTEMI) were included; non-AMI encounters and residents of states without DST were excluded. The primary outcome was in-hospital mortality. Secondary outcomes were in-hospital stroke, reperfusion for STEMI, and revascularization for NSTEMI via percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG). Incidence ratio (IR) compared DST weeks with adjacent weeks, adjusting for the 23-hour “spring forward” and 25-hour “fall back” days.

Generalized estimating equations (GEE) logistic models generated adjusted odds ratios (aORs), accounting for hospital clustering and covariates like demographics, presentation, comorbidities, and laboratory, including body mass index (BMI), left ventricular ejection fraction (LVEF), and troponin relative to the upper limit of normal (ULN). Analyses were conducted in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines. Sensitivity analyses compared DST weeks with three weeks before or after and examined Arizona and Hawaii.

Study results

The final cohort included 168,870 patients treated at 1124 hospitals (median age, 65 years; 57,023 women (33.8%); 111,847 men (66.2%)). In spring, 28,596 patients presented the week before DST, 28,678 during DST week, and 28,169 the week after. In fall, 27,365 presented the week before, 27,942 during DST week, and 28,120 the week after. Baseline demographics, comorbidities, presentation type, and procedural care were closely matched across weeks in both seasons. STEMI comprised 37.4–37.9% in every week examined, with balanced distributions by region and hospital type. Door-to-balloon times remained consistent at 57–58 minutes, coronary angiography use exceeded 91%, primary PCI for STEMI was used in more than 90% of eligible cases in spring and roughly 81% in fall, and revascularization for NSTEMI was stable at 61–63% across all weeks.

Across the entire period, incidence ratios (IRs) showed no significant difference in AMI during spring DST week compared with one week prior or one week after, and no difference for fall DST week versus its adjacent weeks. Year-by-year plots were flat around unity, with one notable exception: in 2020, the spring DST week showed a 21% higher IR compared to the following week and a 6% lower IR compared to the prior week, patterns that overlapped with the onset of coronavirus disease 2019 (COVID-19). Daily analyses during DST weeks mirrored the overall null findings.

In-hospital outcomes were likewise stable. Mortality rates were 4.5% before, 4.6% during, and 4.4% after spring DST; and 4.8% before, 4.9% during, and 4.7% after fall DST. aORs for death comparing DST week with the prior or subsequent week hovered at 1.00–1.02, and adjusted estimates for any stroke were similarly nonsignificant. Subgroup analyses by STEMI and NSTEMI yielded no meaningful differences in aORs across seasons or weeks.

Sensitivity checks supported accuracy: in a separate sensitivity analysis of Arizona and Hawaii, which were excluded from the primary cohort because they do not observe DST, IRs across the corresponding calendar windows were similar; three-week windows were null overall, with an exception in 2020 where IRs were higher in the 3 weeks after spring DST; and excluding 2020-2021 did not change conclusions. Overall, in contemporary practice, clock changes were not associated with surges in AMI presentations or worse in-hospital course.

Conclusions

In this extensive, contemporary registry, DST transitions did not raise AMI incidence or worsen in-hospital outcomes. These findings are consistent across STEMI and NSTEMI strata and adjusted for demographic, clinical, and laboratory covariates using GEE models. For patients, families, and health systems, the message is reassuring: the lost or gained hour is unlikely to trigger heart attacks or complicate hospital care.

Public debate about time standards should weigh other endpoints, such as out-of-hospital cardiac arrest, traffic risk, and sleep health, rather than AMI alone. The authors also note that other conditions, such as ischemic stroke and vehicular crashes, may still show temporal associations with DST changes.