Daylight Savings Time Not Associated with Heart Attack Rates

No significant difference in acute myocardial infarction incidence was identified in the weeks before, during and after daylight savings time in a cross-sectional study involving close to 169,000 patients enrolled in the American College of Cardiology’s collaborative Chest Pain MI Registry.

The analysis also showed no significant differences in mortality while hospitalized or stroke during the different time periods, as well as differences in in-hospital outcomes.

The study findings, published in JAMA Network Open, do not support earlier studies suggesting that adjustment to time changes associated with daylight savings time (DST) may be a heart attack risk factor.

Researcher Jennifer Rymer, MD, of Duke University Hospital, Durham, North Carolina, and colleagues, noted that most of these studies are over a decade old, with the data derived from limited registry datasets.

Findings from one such study involving data from a Swedish MI registry, published as a correspondence in the New England Journal of Medicine in 2008, showed an elevated MI rate for the first 3 workdays after DST in the spring, with the transition out of DST in the fall showing an impact for only 1 workday.

"To our knowledge, (ours) is the largest analysis to date of the association of incidence of AMI and DST," Rymer and colleagues wrote.

"Our findings showed that there was no significant increase in incidence of AMI during the week of DST or in the weeks thereafter. Additionally, we demonstrated that the adjusted risk for in-hospital death, stroke or reperfusion (STEMI) or revascularization (NSTEMI) was not significantly different 1 week before or after the week of spring or fall DST time changes."

The American Chest Pain MI Registry represents a voluntary registry of 1,323 U.S. treatment centers that collect data on consecutive patients admitted with acute myocardial infarction across the United States. Patient medical history, clinical presentation details, treatment details and in-hospital outcomes are collected, and regular audits and data quality checks are performed to ensure accuracy within the registry.

This cross-sectional study examined patients enrolled in the registry from 2013 to 2022 who presented 1 week before DST, during the week of DST, or 1 week after DST (spring or fall). Assessment included AMI incidence, in-hospital mortality, stroke, and clinical outcomes during those times and compared the DST weeks with the week before or after.

Primary study outcomes included incidence ratio (IR) of AMI cases "calculated using the observed number of patients with AMI in the DST week divided by the number of patients with AMI who arrived 1 week before or after DST."

The final cohort included 168,870 patients (median [IQR] age, 65 [56-75] years, 33.8% female) treated at 1,124 hospitals during the study period.

A total of 28,678 patients (17.0%) were treated for AMI during spring DST, 28,596 (16.9%) the week before, and 28 169 (16.7%) the week after, while 27,942 patients (16.5%) with AMI were treated during fall DST, 27,365 (16.2%) the week before, and 28,120 (16.7%) the week after.

Looking at patient characteristics and outcomes, the study authors reported:

• Patients were similar in the spring and fall DST analyses (spring and fall DST median [IQR] age across groups: 65 [56-74] years and 65 [56-75] years, respectively), and there were 28,725 females (33.6%) in the spring and 28,298 females (33.9%) in the fall.
• No significant difference in AMI incidence was observed for both the spring DST week versus 1 week prior or 1 week after, and the fall DST week versus 1 week prior and 1 week after.
• There were no significant differences in adjusted in-hospital outcomes for the 1 week before or after fall or spring DST.
• Sensitivity analyses, which compared the incidence of AMI during the DST weeks with the weeks before or after the DST week in the states of Hawaii and Arizona, where DST does not exist, showed similar incidence ratio patterns over the study period, regardless of AMI type.
• The only period with a large increase in AMI incidence during the study period was the week after spring DST in 2020, which overlapped with the beginning of the COVID-19 pandemic.

"These findings contrast to previous smaller studies which have demonstrated a rise in the incidence of AMI in the week after spring DST," Rymer et al. wrote.

Study strengths, which may have led to the disparate results, included the very large cohort and heterogeneous patient population. Limitations included the possibility of residual confounding and/or information bias due to the retrospective, observational study design.

The researchers concluded that while the study did not show a link between DST and AMI, other studies have linked DST to an increased risk for other deleterious outcomes, including out of hospital cardiac arrest, ischemic stroke and car crashes.

Funding for this study was provided by the NIHLBI and the American College of Cardiology. Rymer reported no relevant disclosures related to this study.

Rymer JA, et al "Daylight savings time and acute myocardial infarction" JAMA Netw Open 2025; DOI: 10.1001/jamanetworkopen.2025.30442.