Daylight Saving and Heart Attacks: The Core Link
Research links the spring transition to daylight saving time with a small but measurable increase in heart attacks in the days that follow. The American Heart Association notes that losing one hour of sleep can disrupt circadian rhythms, blood pressure, and stress responses, which may trigger cardiac events in vulnerable individuals. A study published in the journal Open Heart and reported by Forbes found a spike in hospital admissions for heart attacks during the week after clocks spring forward.
Fall back time, when people gain an hour, appears to have a weaker or neutral effect on heart attack rates, though sleep fragmentation and seasonal factors still matter. The risk is not uniform; people with existing heart disease, hypertension, or sleep disorders face a higher short-term risk. The overall absolute increase in heart attacks is modest, but the pattern is consistent across multiple studies and healthcare systems.
Why the Clock Change Affects the Heart
Sleep Loss and Autonomic Nervous System Shifts
Even a one-hour sleep reduction can raise sympathetic nervous system activity, increase cortisol, and impair glucose regulation, all of which strain the cardiovascular system. Data from hospital networks and insurance claims show a rise in emergency room visits for acute coronary syndromes in the Monday and Tuesday after spring daylight saving time.
Inflammation and Blood Clotting
Experimental sleep restriction studies show short-term increases in inflammatory markers and platelet activation, which can promote plaque rupture and clot formation in coronary arteries. These biological pathways help explain why the daylight saving transition is associated with a transient rise in heart attacks, especially among older adults and those with risk factors like smoking, diabetes, or high cholesterol.
What the Numbers Say About Daylight Saving and Heart Attacks
A 2024 analysis of U.S. hospital data, cited by the American Heart Association and reported by Forbes, found a statistically significant increase in heart attack admissions on the Monday after spring daylight saving compared with other Mondays. The effect was strongest in the first three days after the transition and faded by the end of the week.
Broader population-level data from the CDC and European registries show that the spring clock change coincides with a small but real bump in out-of-hospital cardiac deaths and emergency calls. The fall transition does not show the same clear spike, though some studies note a slight increase in arrhythmia-related visits. Overall, the evidence supports a short-term, time-specific increase in cardiovascular risk tied to the spring daylight saving shift.
Risk Factors and Groups Most Affected
Who Faces the Highest Short-Term Risk
Adults over 65, men, and people with diagnosed cardiovascular disease, diabetes, or obesity appear to have a larger relative increase in heart attack risk after the spring clock change. Shift workers and people with chronic insomnia may also be more sensitive to the sleep disruption caused by daylight saving time.
Geographic and Seasonal Patterns
Regions farther from the equator, where the spring clock change creates a larger shift in sunrise and sunset times, tend to show a more pronounced spike in heart attack admissions. Data from states like Michigan and institutions such as the Mayo Clinic highlight that the combination of lost sleep, darker morning commutes, and seasonal allergies can compound cardiovascular strain in the days after daylight saving time begins.