Climate change increases stroke risk through extreme weather and pollution

The World Stroke Organization is warning that climate change poses an escalating threat to brain health, with extreme heat in particular increasing the risk of having a stroke and of patients dying from stroke.

In a scientific statement published in the International Journal of Stroke, the organization summarises the latest evidence on the association between stroke and the environmental factors exacerbated by climate change.

These include extreme temperatures, temperature variability, humidity, barometric pressure, wildfires, and dust and sandstorms.

Stroke remains a leading cause of morbidity and mortality globally, with 89 per cent of the burden occurring in low to middle-income countries. Ischaemic stroke, which occurs when a blood clot blocks an artery in the brain, is the most common type of stroke. 

Senior lead author Professor Anna Ranta from the Department of Medicine at the University of Otago, Wellington, New Zealand, and a member of the World Stroke Organization's Board of Directors, says an unstable climate increases the risk both of having a stroke and of patients dying as a result.

Temperature extremes and rapid swings in temperature, humidity and air pressure have a physiological effect on the human body. Hot temperatures can cause dehydration, 'thickening' the blood and raising the risk of blocked blood vessels, while humidity and air pressure changes can increase blood pressure, an important cause of stroke.

Absolute changes in temperature and variations in temperature, barometric pressure and humidity – patterns that are intensifying as a result of climate change – all have an impact on stroke risk."

Professor Anna Ranta, Department of Medicine, University of Otago

Professor Ranta says compound weather events, such as when extreme heat and drought, or cold, humidity and wind come together, have an additive effect, increasing the risk of stroke and mortality even further.

"Air pollution is another big factor in increasing the risk of stroke, with more than 20 per cent of strokes globally attributed to air pollution.

"While transport and industrial emissions are primarily a cause, rather than an effect of climate change, increases in frequency and severity of wildfires, sand and dust storms have been directly linked to climate change. The particulate matter of the 'air pollutants' enter the blood stream via the lungs and cause damage to blood vessel walls. This can result in blocked and ruptured brain arteries and cause a stroke."

Older adults, workers frequently exposed to the weather, and those in low and middle-income countries are at higher risk of stroke from environmental factors.

The World Stroke Organization's statement says advancing efforts to reduce greenhouse gas emissions is vital to reduce the environmental drivers of stroke risk and to protect long-term population brain health.

Its key recommendations include stepping up efforts to cut carbon emissions by promoting clean energy, plant-rich diets and active transport around the world; educating patients about weather-related impacts on health; embedding temperature and other climate-related alerts into hospital electronic health records and public messaging; and strengthening interdisciplinary cooperation among meteorological agencies, environmental scientists, urban planners and emergency services to develop coordinated policies for preparedness, early warnings, and responses to climate-related stroke hazards.

The scientific paper was put together by an international panel, led by Professor Ranta, and included experts in climate change and climate medicine, and stroke specialists from New Zealand, Asia, Europe, the Middle East and North Africa, and North and South America.