A study led by Harvard T.H. Chan School of Public Health has found that extreme heat and extreme cold are both associated with increased risks of death from ischemic and hemorrhagic stroke. The researchers discovered that this link was stronger in low-income countries compared to high-income countries. The study will be published on May 22, 2024, in the journal Stroke. Lead author Barrak Alahmad stated that as temperatures become more extreme due to climate change, fatal strokes are expected to increase, with a widening disparity in stroke mortality between high- and low-income countries.
Previous research on the relationship between extreme temperatures and stroke mortality has provided mixed or inconclusive results, with most studies focusing on single cities or countries, mostly high-income. To address these gaps, the researchers utilized a multinational, multiregional database of ischemic and hemorrhagic stroke mortality from the Multi-Country Multi-City Network, comprising over 3.4 million ischemic stroke deaths and more than 2.4 million hemorrhagic stroke deaths reported between 1979 and 2019 across 522 cities in 25 countries. The study found that for every 1,000 ischemic or hemorrhagic stroke deaths, about 11 were attributable to extreme cold or hot days.
The researchers also found that low-income countries bore a higher burden of heat-related hemorrhagic stroke mortality than high-income countries, pointing to differences in indoor temperature control systems, rates of outdoor work, and quality of health care as potential explanations for disparities. Further study is needed to understand the drivers of low-income countries’ higher burden of temperature-related hemorrhagic stroke mortality and identify interventions. Limitations of the study included a limited geographic scope, lack of individual-level demographics, and focus only on stroke deaths.
The researchers called on professional stroke societies to invest more in research on climate change-related environmental risk factors that could exacerbate strokes, which are already a significant driver of mortality worldwide. The study was supported by various funding sources including the Kuwait Foundation for the Advancement of Science, the Medical Research Council-UK, the European Union, the Swiss National Science Foundation, and the National Institutes of Health. Co-authors of the study from Harvard Chan School included Antonella Zanobetti, Joel Schwartz, and Petros Koutrakis. As climate change continues to escalate, understanding the impact of extreme temperatures on stroke mortality is critical for developing interventions to mitigate risks and reduce disparities between high- and low-income countries.