LAUSR

Background Psychosocial stress might trigger myocardial infarction (MI). Increased MI incidence coincides with recurrent time periods during the year perceived as particularly stressful in the population. Methods A stress‐triggering hypothesis on the risk of MI onset was investigated with Swedish population data on MI hospital admission date and symptom onset date (N = 156,690; 148,176) as registered from 2006 through 2013 in the national quality registry database Swedish Web‐system for Enhancement and Development of Evidence‐based care in Heart disease Evaluated According to Recommended Therapies (SWEDEHEART). Poisson regression was applied to analyze daily MI rates during days belonging to the Christmas and New Year holidays, turns of the month, Mondays, weekends, and summer vacation in July compared with remaining control days. Results Adjusted incidence rate ratios (IRRs) for MI rates were higher during Christmas and New Year holidays (IRR = 1.07 [1.04–1.09], P < .001) and on Mondays (IRR = 1.11 [1.09–1.13], P < .001) and lower in July (IRR = 0.92 [0.90–0.94], P < .001) and over weekends (IRR = 0.88 [0.87–0.89], P < .001), yet not during the turns of the month (IRR = 1.01 [1.00–1.02], P = .891). These findings were also predominantly robust with symptom onset as alternative outcome, when adjusting for both established and some suggested‐but‐untested confounders, and in 8 subgroups. Conclusions Fluctuations in daily MI incidence rates are systematically related to time periods of presumed psychosocial stress. Further research might clarify mechanisms that are amenable to clinical alteration.