A recent study led by the Harvard T.H. Chan School of Public Health has found that extreme temperatures and increased mortality from ischemic and hemorrhagic strokes are quite present more in low-income countries than high-income countries.
The study, led by research fellow Barrak Alahmad from the Department of Environmental Health, aims to shed light on the impact of climate change on stroke mortality. As global temperatures continue to rise, the study predicts a corresponding increase in fatal strokes, with a widening mortality disparity between high- and low-income countries.
PREVIOUS RESEARCH GAPS
Prior research on the connection between extreme temperatures and stroke mortality has produced mixed results. Most studies have been limited to specific cities or high-income countries and often did not differentiate between stroke subtypes. This study addresses these gaps by utilizing data from the Multi-Country Multi-City Network, a global environmental health consortium.
METHODOLOGY
The researchers created a comprehensive database of stroke mortality, covering more than 3.4 million ischemic stroke deaths and over 2.4 million hemorrhagic stroke deaths reported between 1979 and 2019. The data spans 522 cities in 25 countries, offering a broad perspective on the issue.
KEY FINDINGS
The study found that for every 1,000 ischemic or hemorrhagic stroke deaths, approximately 11 were attributable to extreme temperature days. The coldest and hottest 2.5% of days contributed to 9.1 and 2.2 excess ischemic stroke deaths, respectively. For hemorrhagic strokes, the same temperature extremes resulted in 11.2 excess deaths due to cold and 0.7 excess deaths due to heat per 1,000 cases.
DISPARITIES BETWEEN INCOME LEVELS
Low-income countries experienced a higher burden of heat-related hemorrhagic stroke mortality compared to high-income countries. The evidence also suggested a higher burden of cold-related hemorrhagic stroke mortality in low-income countries, though this was not conclusively proven. Interestingly, the study did not find a correlation between a country’s gross domestic product (GDP) and the risk of temperature-related ischemic stroke mortality.
POSSIBLE EXPLANATIONS FOR DISPARITIES
The researchers suggest that disparities could be due to better indoor temperature control systems and lower rates of outdoor work in high-income countries. Conversely, worse-quality healthcare in low-income countries might contribute to higher stroke mortality rates. Further research is needed to understand these disparities fully and to identify effective interventions.
STUDY LIMITATIONS AND FUTURE RESEARCH
The study’s geographic scope was limited, under representing rural settings and countries in South Asia, Africa, and the Middle East. Additionally, the study did not collect individual-level demographic data or focus on non-fatal strokes, which could provide a more comprehensive understanding of the burden of temperature-related strokes.
CALL TO ACTION
Lead author Barrak Alahmad emphasized the need for professional stroke societies to invest in further research. As climate change continues to escalate, understanding and mitigating environmental risk factors will be crucial in reducing stroke mortality.
This Harvard-led study highlights the urgent need to address the health impacts of extreme temperatures, particularly in low-income countries. Comprehensive strategies and targeted interventions are essential to mitigate the rising stroke mortality associated with climate change.
