Past research linked daylight saving time to a 24% spike in heart attack trends. Now, Duke University doctors are taking an awakened stance.
If you’ve always met mid-autumn’s “falling back” with the anticipation of a cozy extra hour of sleep, that moment is days away. In recent years, politicians have kicked around the idea of doing away with daylight saving time, while some health experts have chimed in to say the switch-a-roo of the clocks can be tough on heart health. Adam Spira, PhD, MA, a sleep expert and mental health professor at Johns Hopkins University, has commented: “The scientific evidence points to acute increases in adverse health consequences from changing the clocks, including in heart attack and stroke.”
But now a new, decade-long analysis that assessed data from a significant sample size may overturn this assertion. Cardiology research in the September 2025 issue of JAMA Network Open found no meaningful changes in the number, or severity, of heart attacks following either the spring or fall time changes.
The research team, led by Jennifer Rymer, MD, an interventional cardiologist with Duke University Medical Center, analyzed data from more than 1,100 hospitals participating in the Chest Pain MI Registry between 2013 and 2022. On average, about 28,000 people each week were treated for heart attack before, during, and after the clock shifts. The study revealed no consistent week-to-week differences in heart attack incidence or in-hospital outcomes such as stroke or death.
“To our knowledge, this is the largest analysis to date of the association of incidence of AMI [acute myocardial infarction, the scientific term for heart attack] and [daylight saving time],” Dr. Rymer’s team reports. The only “marked increase” that the researchers note occurred in the week after the spring 2020 time change—”a time which would have overlapped with the beginning of the COVID-19 pandemic,” they say. This could be considered an outlier—an anomaly—of a public health trend.
When Dr. Rymer’s group says there was potentially no effect strictly from clock changes for the nearly 170,000 patients who were included, they suggested that gains in cardiac care and changes in modern lifestyles—not to mention their larger and more heterogeneous cohort—may help explain why previous correlations blaming the change of clocks no longer hold.
The study does not exonerate daylight savings time from all health concerns—sleep loss, fatigue, and increased accident risk remain areas of focus. However, it does challenge the notion that the practice directly drives a surge in heart attacks.
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