Hourly Heat Exposure linked to Increased Risk of Acute Ischemic Stroke: JAMA

In a groundbreaking study conducted across more than 200 stroke centers in China, researchers have uncovered a direct and immediate association between hourly high ambient temperatures and the onset of Acute Ischemic Stroke (AIS). While previous studies have explored the broader connection between daily high temperatures and ischemic stroke outcomes, this research uniquely focuses on the hourly nuances of temperature exposure and its impact on AIS. The study's outcomes suggest a significant association between hourly heat exposure and an increased risk of AIS onset.

The study results were published in the journal JAMA Network Open.

The study, structured as a time-stratified case-crossover, aimed to evaluate the association between hourly high ambient temperatures and the onset of AIS. Using a nationwide registry that compiled data from over 82,000 adult AIS patients hospitalized during warm seasons between 2019 and 2021, the research provided a granular examination of temperature exposure in the 24 hours leading up to the stroke onset.

Key Findings:

• The comprehensive analysis included data from 82,455 AIS patients, revealing a mean age of 65.8 years, with 63.4% being male.
• They identified a consistent and escalating risk of AIS onset correlated with higher temperatures.
• Notably, the excess risk of AIS emerged immediately at lag 0 hours, persisting for 10 hours following the temperature exposure.
• The study compared the cumulative odds ratio over lag 0 to 10 hours for AIS onset, revealing a significant association.
• Extremely high temperatures (33.3 °C) were linked to a 1.88-fold increase in the odds of AIS compared to the reference temperature (12.1 °C).
• The exposure-response curve demonstrated regional disparities, with the northern regions exhibiting a steeper curve compared to the southern regions.
• While there were indications of greater odds ratios for males and patients with a history of dyslipidemia or atrial fibrillation, these differences did not achieve statistical significance.

The study's findings hold profound implications for public health strategies, particularly in the context of global warming. Understanding the immediate hourly dynamics of heat exposure and its correlation with AIS onset provides a valuable framework for targeted interventions. The research underscores the importance of adapting public health initiatives to address the specific challenges posed by rising temperatures, ensuring a proactive approach to mitigating the increased risk of AIS associated with ambient heat. As further studies delve into this critical area, these findings pave the way for informed strategies to protect individuals from the cerebrovascular risks linked to elevated temperatures.

Further reading: 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