Study finds no rise in heart attacks around daylight savings time

Duke Clinical Research Institute-led research finds that changing clocks and adjusting to daylight savings time showed no significant association with acute myocardial infarction (AMI, or heart attack) incidence or in-hospital outcomes.

In the US, daylight savings time shifts clocks forward by 1 hour on the second Sunday of March and back again on the first Sunday of November, altering sleep and daily schedules. Previous analyses in Sweden and US cohorts hinted at short-lived increases in MI after the spring shift, including a 24% rise on the Monday after daylight savings time.

In the study, “Daylight Savings Time and Acute Myocardial Infarction,” published in JAMA Network Open, researchers conducted a cross-sectional study to determine whether the incidence of patients presenting with AMI is greater during the week of daylight savings time or the week after, and to compare in-hospital clinical events between the week before and the week after.

A cohort of 168,870 patient data at 1,124 hospitals from 2013 to 2022 was analyzed for the study, drawn from the National Cardiovascular Data Registry Chest Pain–MI Registry. Median age was 65 years, and 33.8% were female.

Data came from patients who arrived in the week before, during, or after the spring or fall clock change. Primary outcome was in-hospital mortality, with stroke, NSTEMI revascularization, and STEMI reperfusion as secondary endpoints.

Incidence ratios compared AMI counts in daylight savings time weeks with adjacent weeks, with 23-hour and 25-hour Sundays normalized to 24 hours. Risk-adjusted comparisons used logistic models with generalized estimating equations to account for hospital clustering. Sensitivity checks included Hawaii and Arizona, nonparticipating DST states, and 3-week windows around the clock change.

Across the 168,870 hospital visits, AMI counts during the spring clock-change week were 28,678, compared with 28,596 in the prior week and 28,169 in the following week. No significant differences were detected for these comparisons.

Fall comparisons were similar: 27,942 during the clock-change week, 27,365 the week before, and 28,120 the week after. No significant differences were detected.

Adjusted models for in-hospital death also did not indicate changes around the transition.

Stroke outcomes showed no significant differences across spring and fall comparisons. Year-by-year incidence ratios clustered near 1.00, with a 21% increase during the week of spring daylight savings time in 2020 vs. the week after and a 6% decrease vs. the week before.

Analyses of areas without clock changes (Arizona and Hawaii) showed incidence ratios that were similar across the study period.

Authors conclude that daylight savings time weeks were not associated with higher AMI incidence or worse in-hospital outcomes when compared with adjacent weeks.

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