[Seasonal variation of sudden death based on analysis of death certificate information]

Seasonal variation of sudden death (SD) was studied based on analysis of death certificates of all 8,519 SD patients, aged 15 years or older, who died during 1984 to 1986 in Niigata prefecture, Japan. SD was defined as death within 24 hours of onset of the underlying cause. SD showed a significantly high incidence during the cold season. When analyzed by underlying cause, the high incidence during cold season was shown for SD by circulatory diseases such as acute myocardial infarction (AMI; n = 1,446), other cardiovascular diseases (OCD; n = 4,375) and cerebrovascular accident (CVA; n = 1,725). However, no significant seasonal variation was observed for SD by non-circulatory diseases. By age group, the incidence of SD due to circulatory diseases was high during the cold season in the elderly (61 to 75 years) and the old age (76 years or older) groups, irrespective of kinds of the diseases, whereas the pattern varied by disease type in the young to middle age group (15 to 60 years). The highest incidence of SD due to AMI in the young to middle age group occurred in January with a second peak in July to August. Thus, not only low temperatures but high temperatures seemed to also contribute to the occurrence of SD by AMI in this age group. While SD due to OCD in this age group did not show a significant seasonal variation, that due to CVA showed a high incidence during cold season similar to the older age groups. These results suggest that factors affecting the occurrence of SD differed according to underlying cause and age of victims.