Involvement of meteorological factors and sex in the occurrence of subarachnoid hemorrhage in Japan.

The sex difference in the seasonal occurrence of subarachnoid hemorrhage (SAH) and the association of meteorological factors in Japan were analyzed in 1006 consecutive patients with SAH in Toyama, Japan from 1996 to 2000. The study investigated whether these meteorological factors could explain the seasonality of the incidence of SAH in each sex. Seasonal variation of SAH occurrence peaked in spring in men, but peaked in spring and winter in women. The difference between maximum temperature and minimum temperature was the greatest on the day previous to SAH occurrence in multiple individuals in men, whereas mean humidity was the greatest on that day in women. Interestingly, the difference between maximum temperature and minimum temperature peaked in spring and mean humidity in winter from the meteorological data over the 5 years. The relationship between humidity and occurrence of SAH may explain the sex difference of the incidence of aneurysmal SAH. The humidity change may be a specific and additional meteorological factor for the incidence of SAH in women.