Hotter Outdoor Temps Raise Acute Ischemic Stroke Risk for Up to 10 Hours

Exposure to high temperatures was associated with an increased risk of acute ischemic stroke (AIS) onset at an hourly level, according to results from national case-crossover study in China published in JAMA Network Open.

“While some case-crossover studies had been conducted on a daily scale, they had estimated association values that were smaller in magnitude compared with the present study,” wrote corresponding authors Jing Zhao, PhD, and Haidong Kan, PhD, of Fudan University in Shanghai, China, and study coauthors. “We consistently observed higher ORs [odds ratios] for acute heat exposure in lag 0 hours, indicating that the risk of AIS associated with extremely high temperature may not be long lasting.”

The analysis included registry data for 82,455 adults hospitalized with AIS between 2019 and 2021. Researchers looked at links between onset of AIS and hourly temperatures as well as single-hour temperature exposure lags up to 24 hours before AIS onset.

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Higher temperatures were associated with a monotonically increasing risk of AIS onset, according to the study. The increased risk started at the hour of exposure and persisted over 10 hours.

Nationwide, the cumulative OR of AIS onset was 1.88 with a temperature of 33.3 °C, which is equal to about 92 °F, compared with a temperature of 12.1 °C, or about 54 °F. The association between high temperature and AIS onset was steeper in northern China (researchers reported a 1.80 OR) than southern China (1.57 OR).

“This regional discrepancy may be due to the better heat adaptability for populations in the south where the climate was warmer, which is consistent with previous findings,” researchers wrote.

ORs were also higher for men and patients with a history of dyslipidemia or atrial fibrillation. However, the differences between the subgroups were not statistically significant.

“The results add valuable insights to the adverse cardiovascular outcome of climate warming and may benefit the formulation of public health strategies to reduce cerebrovascular risk associated with high ambient temperature under global warming,” researchers wrote. “Additionally, the findings underscore the ongoing need for public health agencies to advocate for interventions that mitigate heat exposure and bolster cooling measures, particularly among populations at high risk for AIS.”

Reference

Zhu X, Chen R, Yuan J, et al. Hourly heat exposure and acute ischemic stroke. JAMA Netw Open. 2024;7(2):e240627. doi:10.1001/jamanetworkopen.2024.0627