Weather Fluctuations May Have an Impact on Stroke Occurrence in a Society: A Population-Based Cohort Study.

Background: Stroke has been found to have a seasonally varying incidence; blood pressure, one of its risk factors, is influenced by humidity and temperature. The relationship between the incidence of stroke and meteorological parameters remains controversial.

Objective: We investigated whether meteorological conditions are significant risk factors for stroke, focusing on the fluctuation of weather elements that triggers the onset of stroke.

Methods: We collected ambulance transportation data recorded by emergency personnel from Gifu Prefecture. We included cases where the cause of the transportation was stroke and excluded cases of trauma. We combined these data with meteorological data as well as data on average temperature, average air pressure, and humidity provided publicly by the Japan Meteorological Agency. Our target period was from January 2012 to December 2016.

Results: In the 5-year target period, there were 5,501 occurrences of ambulance transportation due to stroke. A seasonal tendency was confirmed, since ambulance transportation for stroke occurred more frequently at low temperatures (p < 0.001). Temperature (odds ratio: 0.91; p < 0.001) and humidity change (odds ratio: 1.50; p = 0.016) were identified as risk factors for ambulance transportation due to stroke. An increase in temperature incurs a lower risk than a decrease (odds ratio: 0.58; p = 0.09), although there is no statistically significant difference.

Conclusions: Meteorological effects on the frequency of ambulance transportation due to stroke were studied. A lower temperature and radical humidity change were identified as risk factors for ambulance transportation due to stroke, and a decrease in temperature was also associated. We speculate on the possibilities of using meteorological data to optimize the assignment of limited medical resources in medical economics.