Extremely high or extremely low temperatures could increase the risk of fatal stroke, warns a new study involving a Canadian researcher.
This apparent increase in risk applies both to hemorrhagic strokes, when bleeding occurs in the brain, and to ischemic strokes, when an artery that supplies blood to the brain is blocked by a clot, explain the authors of the study. ‘study.
We are hearing more about the impact of climate change on the risk of cardiovascular disease, recalled Professor Éric Lavigne of the University of Ottawa.
“In terms of stroke, it’s something that is perhaps a little less known, but which is still very important because it can be very dangerous, and obviously it can be fatal,” he said. .
Researchers analyzed a database that lists more than 2.4 million deaths caused by hemorrhagic stroke and 3.4 million deaths caused by ischemic stroke. These deaths were reported between 1979 and 2019 in 522 cities across 25 countries. The researchers also had data on the daily temperature in each city.
Using sophisticated statistical analyses, they found that for every 1,000 deaths caused by hemorrhagic or ischemic stroke, eleven were attributable to the hottest and coldest days. The coldest days are thought to cause about four times as many additional deaths as the hottest days.
“The impact of cold temperatures had already been documented in the past,” said Mr. Lavigne. We knew that hot temperatures had an impact on the cardiovascular level, but we still see specific impacts on strokes. »
The burden of the impact of extreme temperatures was greater for cold temperatures, Lavigne added, meaning that there were more excess deaths that were attributable to extremely cold temperatures than to extremely hot temperatures.
On the other hand, he continues, the risks when hot temperatures increase are generally higher.
“Ultimately, our message is to be very vigilant from a public health point of view when temperatures are both very hot and very cold, because we will still continue to have cold waves “, he said.
People with pre-existing conditions, such as hypertension or high cholesterol, are likely more vulnerable than others to extreme temperatures, Lavigne said.
When it is very cold, for example, the blood vessels may contract, the blood will circulate less well, “and if we also have someone who has hypertension problems or a high cholesterol level, that can make so that it will lead to an ischemic or hemorrhagic stroke.”
Extreme heat can increase the level of inflammation, possibly causing a stroke.
“There are physiological processes that may be different, but we really think that people who have pre-existing illnesses (are more at risk),” said Mr. Lavigne.
The analysis also found that the mortality burden attributable to heat-associated hemorrhagic stroke was greater in less affluent countries than in wealthy countries. Data regarding heat-associated hemorrhagic strokes were less conclusive.
Multiple factors could explain this situation. The authors cite, for example, better access to air conditioning and green spaces in rich countries, or even poorer warning systems to warn the population, higher rates of outside work and less health care. good quality in less well-off countries.
Experts have long warned that poor countries will be more affected by climate change than rich countries. It appears that we must now add public health risks to rising sea levels, droughts and more devastating storms that already threatened them.
“As climate change continues to exacerbate these extreme temperatures, intervention strategies are needed to mitigate the impact on stroke mortality, particularly in low-income countries,” warn the study authors.