When throughout the year is coronary death most likely to occur? A 12-yearpopulation-based analysis of more than 220 000 cases

Background-Previous studies have suggested that there is an increase in car diac events in the morning. Fewer data relate cardiac events to months of t he year and season. Methods and Results-We analyzed all monthly death certificate data from Los Angeles County, California, for death caused by coronary artery disease fr om 1985 through 1996 (n = 222265), The mean number of deaths was highest in December at 1808 and January at 1925, the lowest rates were in June, July, August, and September at 1402, 1424, 1418, and 1371, respectively. Decembe r and January had significantly higher rates than would be expected from a uniform distribution of monthly deaths (P = 0.00001). The percent of yearly coronary deaths was defined by the quadratic U-shaped equation [percent = 13.1198-1.5238(month)+0.0952(month(2)) when January = 1, February = 2, etc] . When monthly deaths were plotted by year, there was a decrease from 1985 through 1996. Monthly mortality correlated inversely with temperature. Duri ng the months with the highest frequency of death (December, January), howe ver, there was an increase in deaths that peaked around the holiday season and then fell, which could not be explained solely on the basis of the dail y temperature change. Conclusions-Even in the mild climate of Los Angeles County, there are seaso nal variations in the development of coronary artery death, with approximat e to 33% more deaths occurring in December and January than in June through September. Although cooler temperatures may play a role, other factors suc h as overindulgence or the stress of the holidays might also contribute to excess deaths during these peak times.