Time Changes Appear to Affect Heart Attack Incidence

Rate higher in days after spring transition and lower following fall switch in Swedish population

WEDNESDAY, Oct. 29 (HealthDay News) -- The switch to daylight saving time in the spring was followed by an increased incidence of acute myocardial infarction in Sweden during the past two decades, according to research published in the Oct. 30 New England Journal of Medicine.

Imre Janszky, M.D., Ph.D., of the Karolinska Institute and Rickard Ljung, M.D., Ph.D., of the National Board of Health and Welfare, both in Stockholm, Sweden, analyzed data from a comprehensive Swedish registry of myocardial infarctions (MIs) dating back to 1987. The authors calculated the incidence ratio for each of the seven days following the spring and autumn time shifts by dividing the incidence on each day by the mean of the incidence on that day of the week two weeks earlier and two weeks later.

The incidence of acute MI was significantly increased for the first three weekdays after the shift to daylight saving time in the spring, and the incidence ratio for the first week after the transition was 1.051. After the autumn transition, the first weekday had a significant drop, with the incidence ratio for the whole week at 0.985.

"The most plausible explanation for our findings is the adverse effect of sleep deprivation on cardiovascular health. According to experimental studies, this adverse effect includes the predominance of sympathetic activity and an increase in proinflammatory cytokine levels," the authors write. " The finding that the possibility of additional sleep seems to be protective on the first workday after the autumn shift is intriguing."

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