High ambient temperature in summer and risk of stroke or transient ischemic attack: A national study in Israel

Objective: To examine whether high ambient temperature and diurnal temperature range during the summer are associated with risk of stroke/transient ischemic attack (TIA). Methods: A time-stratified case-crossover study design was conducted. The study sample comprised all individuals aged >= 50 years who had a stroke/TIA reported to the Israeli National Stroke Registry between 2014 and 2016 during the summer season. Daily temperature data were retrieved from the Israel Meteorological Service. Conditional logistic regression models were used with relative humidity and air pollution as covariates. Results: The sample included 15,123 individuals who had a stroke/TIA during the summer season (mean age 73 +/- 12 years; 54% males). High ambient temperature was associated with stroke/TIA risk starting from the day before the stroke event, and increasing in strength over a six-day lag (OR = 1.10 95%CI 1.09-1.12). Moreover, a larger diurnal temperature range prior to stroke/TIA occurrence was associated with decreased stroke/TIA risk (OR = 0.96 95%CI 0.95-0.97 for a six-day lag). Conclusions: High ambient temperature may be linked to increased risk of cerebrovascular events in subsequent days. However, relief from the heat during the night may attenuate this risk.