(DURHAM, NC) As most Americans prepare to turn their clocks back one hour on Sunday, Nov. 2, a new study is casting doubt on a long-standing belief: that daylight saving time (DST) disrupts sleep enough to trigger a spike in heart attacks.
In a sweeping analysis of nearly 170,000 patients over a decade, researchers at Duke University School of Medicine found no significant increase in heart attacks during the weeks surrounding DST transitions — in neither spring nor fall.
The findings published Sept. 9 in JAMA Network Open challenge earlier, smaller studies that suggested the spring time change, which robs people of an hour of sleep, could lead to a rise in cardiovascular events.
The only exception in the new study was a spike in acute myocardial infarction (AMI) cases following spring DST in 2020, coinciding with the onset of the COVID-19 pandemic, a period of widespread stress, uncertainty, and disruptions to health care.
“This is the most comprehensive look we’ve had at the relationship between DST and heart health,” said lead study author Jennifer Rymer, MD, an interventional cardiologist at Duke Health and an associate professor of medicine at Duke School of Medicine. “And the data simply don’t support the idea that changing the clocks causes a surge in heart attacks.”
The study, published using data from the American College of Cardiology Chest Pain MI Registry, examined cases from 2013 to 2022, with analysis conducted between March 2024 and May 2025.
Daylight saving time is the practice of changing clocks twice a year to take advantage of a longer day in warmer months. Lawmakers continue to debate whether to make DST permanent, or to end it altogether.
Still, the researchers caution that sleep remains a critical factor in heart health. Poor sleep and extremes in sleep duration — less than six hours and more than nine hours — have been consistently linked with cardiovascular risks.
Duke, along with colleagues, compared heart attack rates during the week of DST — both spring and fall — with the weeks immediately before and after. In the spring, 28,678 patients (17.0%) were treated for AMI during the DST week, compared to 28,596 (16.9%) the week before and 28,169 (16.7%) the week after.
Fall numbers showed a similar pattern: 27,942 patients (16.5%) during DST week, 27,365 (16.2%) the week prior, and 28,120 (16.7%) the week following.
Patient demographics remained stable throughout the study, with a median age of 65 and women making up about one-third of cases.
Researchers found no meaningful differences in hospital deaths, strokes, or other outcomes tied to daylight saving time.
“Advances in post-heart attack treatment over the past decade may also explain why our study did not find statistically significant changes in outcomes, unlike earlier, smaller studies,” said Rymer, who performs procedures, such as angioplasty and stent placement, to quickly open blocked coronary arteries and stop heart attacks.
The study’s authors suggest that previous findings may have been skewed by smaller sample sizes and limited geographic scope.
The broader scope and inclusion of states like Arizona and Hawaii — where DST is not observed — in the new study helped provide a natural control group and perhaps a more accurate picture.
“There are many reasons why heart attacks might become more common during certain times of the year — like when there’s a spike in flu cases or other respiratory illnesses,” Rymer said. “So, while this study looked at heart attack rates around daylight saving time, it’s important to remember that other seasonal factors could also be playing a role.”
Sleep Still Matters
Still, the researchers caution that sleep remains a critical factor in heart health. Poor sleep and extremes in sleep duration — less than six or more than nine hours — have been consistently linked to increased cardiovascular risk.
One hour of additional sleep, studies show, can reduce the risk of heart attack by as much as 20% in short sleepers.
As work schedules have become more flexible and remote jobs more common since the COVID-19 pandemic, the one-hour shift caused by daylight saving time may no longer disrupt daily routines as much as it once did.
With fewer rigid work-hour boundaries and more digital connectivity, the time change may have less impact on sleep patterns and overall health.
While the new findings may ease fears about heart attacks, other studies have linked the time change to increased risk of stroke, car accidents, and workplace injuries.
Additional Authors: Shung Li, Karen Chiswell, PhD, Aman Kansal, MD, Michael G.Nanna, MD, Jorge Antonio Gutierrez, MD, Dmitriy N Feldman, MD, Suni V. Rao, MD, and senior author Rajesh V. Swaminathan, MD.
Funding: American College of Cardiology