The study led by Harvard T.H. Chan School of Public Health discovered that extreme heat and cold are linked to higher risks of death from both ischemic and hemorrhagic stroke. This association was found to be more significant in low-income countries compared to high-income countries.The study will be published on May 22, 2024, in Stroke. Lead author Barrak Alahmad, a research fellow in the Department of Environmental Health, stated that the findings of the study are an important step in understanding the impact of climate change on stroke. With temperatures becoming more extreme, the research anticipates an increase in fatal strokes and a growing difference in stroke mortality rates between high-income and low-income countries, as the latter are expected to be the most affected by climate change. Previous research into the connection between extreme temperatures and stroke mortality has resulted in findings that are similar to those of this study.The results of previous studies on stroke mortality have been mixed and inconclusive. Most of these studies have focused on single cities or countries, especially those with high-income levels, and have not distinguished between different types of stroke. In order to fill these gaps, the researchers used the Multi-Country Multi-City Network, a global consortium focused on environmental health, to create a database of ischemic and hemorrhagic stroke mortality on a multinational and multiregional level. The database included information on over 3.4 million ischemic stroke deaths and over 2.4 million hemorrhagic stroke deaths, reported between 1979 and 2019 in 522 cities across 25 countries.
The study revealed that for every 1,000 cases of ischemic or hemorrhagic stroke, there were significant variations in mortality rates between different regions and countries.According to a study, among the deaths caused by ischemic stroke, approximately 11 were linked to extremely cold or hot weather. Specifically, the coldest and hottest 2.5% of days led to 9.1 and 2.2 excess deaths, respectively. In terms of hemorrhagic strokes, the coldest and hottest 2.5% of days contributed to 11.2 and 0.7 excess deaths out of every 1,000 cases. The study also revealed that low-income countries experienced a higher impact of heat-related hemorrhagic stroke deaths compared to high-income countries. There was also a suggestion that low-income countries may bear a higher burden of cold-related hemorrhagic stroke deaths, but the evidence was not conclusive. The study did not find any correlation between a country’s gross domestic product and the incidence of stroke deaths.The study focused on the relationship between outdoor temperature and the risk of ischemic stroke mortality. The researchers suggested that differences in indoor temperature control and rates of outdoor work in high-income countries, as well as variations in healthcare quality in low-income countries, could account for the disparities. They emphasized the need for further research to understand the reasons behind the higher burden of temperature-related hemorrhagic stroke mortality in low-income countries and to identify effective interventions. The study’s limitations included its geographic scope, which was limited to rural areas and countries in South Asia, Africa, and the Middle East.Underrepresented populations were not included in the study, and individual-level demographics were not collected or analyzed. The focus of the research was solely on stroke deaths, but further investigation into the occurrence of non-fatal strokes would enhance our understanding of the impact of temperature on strokes.
“We urge professional stroke societies to allocate more resources to this type of research, especially as climate change continues to worsen, and to bring attention to emerging environmental risk factors that will exacerbate the already significant global mortality rate due to strokes,” Alahmad stated.
Other co-authors from Harvard Chan rnrn
Antonella Zanobetti, Joel Schwartz, and Petros Koutrakis were involved in the study.
The study received support from the Kuwait Foundation for the Advancement of Science (grant CB21-63BO-01), the Medical Research Council-UK (grant MR/V034162/1), the European Union’s Horizon 2020 Project Exhaustion (grant 820655), the Swiss National Science Foundation (grant TMSGI3_211626), and the National Institutes of Health (grant R01ES034038).
