Daylight saving time shifts and incidence of acute myocardial infarction--Swedish Register of Information and Knowledge About Swedish Heart Intensive Care Admissions (RIKS-HIA).

Background: Daylight saving time shifts can be looked upon as large-scale natural experiments to study the effects of acute minor sleep deprivation and circadian rhythm disturbances. Limited evidence suggests that these shifts have a short-term influence on the risk of acute myocardial infarction (AMI), but confirmation of this finding and its variation in magnitude between individuals is not clear.

Methods: To identify AMI incidence on specific dates, we used the Register of Information and Knowledge about Swedish Heart Intensive Care Admission, a national register of coronary care unit admissions in Sweden. We compared AMI incidence on the first seven days after the transition with mean incidence during control periods. To assess effect modification, we calculated the incidence ratios in strata defined by patient characteristics.

Results: Overall, we found an elevated incidence ratio of 1.039 (95% confidence interval, 1.003-1.075) for the first week after the spring clock shift forward. The higher risk tended to be more pronounced among individuals taking cardiac medications and having low cholesterol and triglycerides. There was no statistically significant change in AMI incidence following the autumn shift. Patients with hyperlipidemia and those taking statins and calcium-channel blockers tended to have a lower incidence than expected. Smokers did not ever have a higher incidence.

Conclusions: Our data suggest that even modest sleep deprivation and disturbances in the sleep-wake cycle might increase the risk of AMI across the population. Confirmation of subgroups at higher risk may suggest preventative strategies to mitigate this risk.