A study led by Harvard T.H. Chan School of Public Health has identified a significant association between extreme temperatures and increased risks of death from both ischemic and hemorrhagic stroke. Scheduled for publication on May 22, 2024, in Stroke, the research underscores that this relationship is particularly pronounced in low-income countries compared to their high-income counterparts.
Lead author Barrak Alahmad, a research fellow in the Department of Environmental Health, highlighted the study’s implications for understanding climate change’s impact on stroke mortality. He emphasised that as temperatures become more extreme, fatal strokes are anticipated to rise, potentially exacerbating the disparity in stroke mortality between high- and low-income countries, with the latter likely bearing a disproportionate burden of climate-related health impacts.
Prior investigations into the correlation between extreme temperatures and stroke mortality have yielded inconsistent findings. Many studies have been confined to single cities or countries, predominantly in high-income regions, and few have differentiated between ischemic and hemorrhagic stroke subtypes. To address these gaps, the researchers leveraged the Multi-Country Multi-City Network, a global consortium in environmental health, to compile a comprehensive database spanning 522 cities across 25 countries. This dataset encompassed over 3.4 million ischemic stroke deaths and 2.4 million hemorrhagic stroke deaths reported between 1979 and 2019.
The study reveals that extreme cold and hot days contributed significantly to stroke mortality. Specifically, for every 1,000 deaths from ischemic or hemorrhagic stroke, approximately 11 were attributable to extreme temperatures. The coldest and hottest 2.5% of days were associated with 9.1 and 2.2 excess deaths from ischemic stroke, respectively, and 11.2 and 0.7 excess deaths from hemorrhagic stroke, respectively. Notably, low-income countries experienced a higher burden of heat-related hemorrhagic stroke mortality compared to high-income countries. However, evidence linking cold temperatures to hemorrhagic stroke mortality in low-income countries was suggestive rather than conclusive. Interestingly, the study did not find a clear relationship between a country’s GDP and the risk of temperature-related ischemic stroke mortality.
The researchers hypothesised that factors such as better indoor temperature regulation and lower rates of outdoor work in high-income countries, coupled with poorer-quality healthcare infrastructure in low-income countries, may contribute to these disparities. They stressed the need for further investigation to elucidate the underlying drivers behind the heightened vulnerability of low-income countries to temperature-related hemorrhagic stroke mortality and to identify effective interventions.
The study’s limitations include its geographical focus, with rural areas and regions in South Asia, Africa, and the Middle East being underrepresented. Additionally, the study did not collect or analyse individual-level demographic data. Furthermore, the focus solely on stroke deaths underscores the necessity for additional research into the incidence of non-fatal strokes to comprehensively assess the overall burden of temperature-related stroke impacts.
Alahmad urged professional stroke societies to invest more in such research, particularly as climate change escalates, and to spotlight emerging environmental risk factors that could exacerbate strokes, already a significant contributor to global mortality rates. He emphasised the importance of expanding this research to inform better public health policies to mitigate the adverse health effects of climate change.
This study by Harvard T.H. Chan School of Public Health underscores the critical link between extreme temperatures and stroke mortality, highlighting the urgent need for targeted interventions, especially in low-income countries most vulnerable to climate change’s health impacts. As global temperatures continue to rise, understanding and addressing these risks will be essential in mitigating the future burden of stroke morbidity and mortality worldwide.
More information: Barrak Alahmad et al, Extreme Temperatures and Stroke Mortality: Evidence From a Multi-Country Analysis, Stroke. DOI: 10.1161/STROKEAHA.123.045751
Journal information: Stroke Provided by Harvard T.H. Chan School of Public Health
