Cold snaps, snowfall and sudden death from ischemic heart disease.

The short-term effect of low temperature on the incidence of ischemic heart disease over a 15-year period was examined. To reduce confounding by other seasonal factors the analysis was restricted to the winter months and was based on the change in the daily rate of sudden death at the time of cold snaps (arbitrarily defined as days on which the mean temperature was at least 4.4 degrees C lower than the day before) and around the time of heavy snowfalls. A statistically significant increase in the daily rate of sudden death at the time of cold snaps occurred only in men under 65 years of age, and even in this group the effect was of relatively small magnitude (+16%) compared with the large change in rate following heavy snowfalls (+88%). Among persons aged 65 years or over cold snaps had virtually no effect, and only the men in this group showed an increased daily rate of sudden death following a snowfall. These results suggest that much of the increased frequency of death from ischemic heart disease in winter, particularly among the elderly, must be due to factors other than short-term cold stress.