Extreme heat increases the risk of stroke: here’s why

Extreme heat increases the risk of stroke: here’s why


OfLaura Cuppini

Chinese study on over 80 thousand people: the probability of an attack rises immediately with extreme heat (therefore particularly in the central hours of the day) and remains high for at least ten hours

2023 was the hottest year since the Earth’s “temperature” was measured (1850), according to the European Copernicus agency. And 2024 could even be worse. A problem for the health of the planet, but also for ours: for example, according to a Chinese study, extreme heat increases the probability of the onset ofacute ischemic strokethat is to say the closure of a cerebral artery, resulting in a reduction in blood and oxygen supply to the brain. A very serious condition, which can lead to disability and death. The analysis, conducted by Fudan University in Shanghai and published on Jama Network Openinvestigated the connections between exposure to high temperatures and increased risk of ischemic stroke and is based on data from 82,455 patients. Result: the probability of an attack increases immediately with extreme heat (therefore particularly in the central hours of the day) and they remain high for at least ten hours.

Who is most at risk

The association between high temperature and hospitalizations/mortality for ischemic stroke had already been highlighted by previous studies, but the “hourly” link between environmental heat and the onset of the attack was not entirely clear. To demonstrate this, the authors examined data from beyond 200 Stroke Units (Stroke Treatment Centers) in China on adult patients (average age 65.8 years) hospitalized in the hot seasons between January 1, 2019 and December 31, 2021. The risk of stroke, in the presence of temperatures above 30 degreeswas greater for males and patients with a history of dyslipidemia (alterations in the amount of lipids in the blood, in particular cholesterol, triglyceridesphospholipids), hypertension or atrial fibrillation. Other established risk factors for ischemic stroke are hypertension, cigarette smoking, poor diet, sedentary lifestyle and air pollution.

More frequent after the age of 55

In Italy, stroke is the second cause of death, after ischemic heart diseases (insufficient supply of blood and oxygen to the heart muscle), is responsible for 9-10% of all deaths and represents the leading cause of disability. Every year they are registered in our country approximately 90 thousand hospitalizations due to brain stroke, of which 20% are relapses. Mortality is very high: 20-30% of people affected by a stroke die within a month and 40-50% within a year. Only 25% of stroke survivors recover completely, 75% must live with some form of disability and of these, half suffer from such a serious deficit that they lose self-sufficiency. Attacks are more frequent after the age of 55 and in males; 75% of strokes occur in people over 65.

Preventive strategies

«Our results indicate a strong link between heat exposure and increased risk of ischemic stroke, underlining the urgency of preventive strategies during periods of extreme heat” commented Xinlei Zhu of Fudan University, one of the authors of the work. The biological mechanisms underlying the association between high temperature and the onset of stroke are not yet completely clear: the heat could increase skin blood flow and sweating, leading to dehydration and consequent increase in blood concentration and viscosity. These factors may be associated with the formation of clots (thromboembolism) and therefore an increased risk of ischemic stroke. Chinese researchers conclude that people at risk of stroke, in particular males with dyslipidemia, hypertension or atrial fibrillationthey should exercise cautiously, reduce outdoor activities and use air conditioning on days when temperatures are very high.

March 8, 2024



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