Absolute Temperature, Temperature Changes and Stroke Risk: A Case-Crossover Study

Studies suggest that there is an association between weather patterns and ischemic stroke risk. Exposure to a sudden decrease in temperature may increase stroke risk through altering blood viscosity and/or by triggering infections. We investigated the association between ischemic stroke risk and change in temperature. We used a case-crossover study design with 303 consecutive patients admitted to Heidelberg University, Department of Neurology over a one and a half year period (Aug 1998–Jan 2000). We used one day before stroke as the hazard (case) period matched to two control periods 2–7 days before and after stroke onset and took both ambient maximum temperature and the 24-hour difference in maximum temperature as exposure. There was no risk associated with ambient maximum temperature at all lag times and in all subgroup analyses. For the 24-hour difference, large changes in temperature (>5 °C) were associated with an increased risk of acute ischemic stroke regardless of whether the change was negative or positive. The odds ratio for temperature increases >5 °C compared to no change in temperature was 2.0 (95% confidence interval (CI): 0.7–5.9) at a lag time of 3 days. We found no relevant relation between temperature and stroke risk. The results suggest that the risk of ischemic stroke may increase with large day-to-day variations upwards or downwards in temperature.