Introduction: Circadian rhythm disturbance increases cardiovascular risk but the effects of daylight saving time (DST) transitions on the risk of myocardial infarction (MI) are unclear.
Methods: We studied association of DST transitions in 2001-2009 with incidence and in-hospital mortality of MI admissions nationwide in Finland. Incidence rations (IR) of observed incidences on seven days following DST transition were compared to expected incidences.
Results: Incidence of MI increased on Wednesday (IR 1.16; CI 1.01-1.34) after spring transition (6298 patients' cohort). After autumn transition (8161 patients' cohort), MI incidence decreased on Monday (IR 0.85; CI 0.74-0.97) but increased on Thursday (IR 1.15; CI 1.02-1.30). The overall incidence of MI during the week after each DST transition did not differ from control weeks. Patient age or gender, type of MI or in-hospital mortality were not associated with transitions. Renal insufficiency was more common among MI patients after spring transition (OR 1.81; CI 1.06-3.09; p < 0.05). Diabetes was less common after spring transition (OR 0.71; CI 0.55-0.91; p = 0.007), but more common after autumn transition (OR 1.21; 1.00-1.46; p < 0.05).
Conclusions: DST transitions are followed by changes in the temporal pattern but not the overall rate of MI incidence. Comorbidities may modulate the effects DST transitions.
Keywords: Acute coronary syndrome; chronobiology; circadian rhythm; circadian rhythm misalignment; daylight saving time; myocardial infarction; risk.