A new UWC study shows that a sudden change in temperatures to either too hot or cold can cause strain in the heart and increase the risk of strokes and heart failures. Illustration: John Thwaits/UWCSudden drops in temperatures between hot and cold, now occurring more frequently as climate change intensifies, are associated with a higher risk of stroke and heart failure in Africa, with elderly women facing the highest risk of death - a new review by the University of the Western Cape (UWC) has revealed.
Conducted with researchers from the South African Research Council (SAMRC), University of Limpopo, University of Cape Town, National University of Lesotho, and Ugandan-based Clarke International University, the review found that extreme heat above 37°C was associated with a rise in heart failures and strokes, while sudden drops of more than 2.4°C raised the risk of stroke by 43%.
Moderate temperatures (20 - 23°C) combined with air pollution intensified health risks for older people above 65 and women were more likely to be admitted to hospital when air pollution levels rose.
Titled “A systematic review assessing the association between extreme temperature exposure and cardiovascular health outcomes in Africa”, researchers analysed 16 studies conducted across Africa between January 1990 and October 2024.
The review noted that the most robust evidence came from South Africa, Mozambique and Burkina Faso.
Hypertension emerged as a major contributing factor to strokes, with evidence showing that more than a third (37.6%) of stroke patients had pre-existing high blood pressure, and about 86.2% of heat-related strokes occurred among these individuals.
Led by Grace Sello, a predoctoral fellow at UWC’s School of Public Health and lecturer at the National University of Lesotho, the review, published in the December issue of Environmental Health, is the first comprehensive assessment of how extreme temperatures affect cardiovascular health in Africa.
Sello said the rise in cardiovascular disease, combined with increasingly severe climate-related events in Southern Africa, makes it urgent for governments to integrate climate adaptation into health policy.
“Strengthening early warning systems, clinical readiness, and targeted care for vulnerable groups will be critical to building resilient health infrastructure and mitigating climate-driven health burdens,” she said.
The most vulnerable groups to cardiovascular conditions linked to the climate-change-related rise and dips in temperatures are women, older people, and those living in rural areas. Researchers, however, say further studies are needed to validate and deepen the understanding of these findings which can help guide public health strategies and strengthen climate adaptation policies.
The World Health Organization (WHO) attributes about 37% of heat-related deaths to human-induced climate change - a long-term shift in weather patterns driven by human activities like burning fuels that release greenhouse gases into the air, resulting in extreme weather events. Over the last two decades, heat-related deaths among people over 65 have risen by 70%, and the WHO estimates that between 2030 and 2050, climate change is expected to cause about 250 000 additional deaths per year from undernutrition, malaria, diarrhoea and heat stress alone. In South Africa, cardiovascular disease, which includes stroke and heart disease, is the leading cause of death after HIV/Aids, responsible for one in six deaths.
The review noted that while high-income countries have well-documented links between extreme temperatures and cardiovascular deaths, similar evidence in Africa has been scarce, with the scale of the problem largely hidden due to weak health surveillance systems.
They say the sudden dips in temperature may increase the risk of strokes and heart failures by causing direct physiological changes, with cold weather associated with the elevation of blood pressure that puts strain on the heart and increases clotting risks, while extreme heat may cause dehydration and abnormal heart rhythm that may trigger heart attacks and strokes.
A South African study found that people living in inadequate housing, without heating and on very low incomes below $73 (about R1,250) face a higher risk of cold-related cardiovascular deaths. In Mozambique, a sudden drop in minimum temperature of more than 2.4 °C was linked to a 43% increase in stroke risk. In countries that experience higher temperatures between 33 °C - 38 °C, such as Niger and Burkina Faso, heat exposure was linked with a high rate of strokes and heart failures, and mortality.
Researchers said the latest findings not only provide clear data on the impact of climate change on cardiovascular disease in Africa, but they will also help guide public health strategies and strengthen climate adaptation policies for Africa, where cardiovascular disease has more than doubled over the last 30 years.
