As the Earth continues to warm, the rising temperatures are contributing to a number of health conditions that are in turn driving up mortality. And for the first time, scientists have figured out a more detailed way to estimate how many deaths can be attributed to heat.
In a paper published in Nature Medicine, researchers in Spain and France calculated that more than 61,000 deaths in Europe could be blamed on the heat during the summer of 2022, the hottest summer on record for the continent. (At least until the readings from 2023 are analyzed later this year.)
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“We are probably not aware of how heat is a silent killer,” says Joan Ballester, professor at ISGlobal, a private research foundation in Barcelona, and lead author of the paper.
While health experts have known that rising temperatures can contribute to an increase in potentially fatal conditions such as heat stroke and an increase in heart-related events such as heart attacks, irregular heart beats, and even heart failure, few studies have quantified how much heat can contribute to higher mortality. Using carefully calibrated data on temperatures recorded during the peak of the European heat wave in 35 countries from the end of May to the beginning of September last summer, and correlating that information with more than 45 million similarly temporally calibrated deaths across Europe, the scientists found a strong association between increased temperatures and higher mortality. They adjusted for the fact that deaths would lag by a few days behind periods of high temperatures, as the health effects of heat may take a few days to manifest, as well as for the expected mortality in the absence of excessive heat. After creating models that tracked short-term fluctuations in temperature and mortality, they found that on warmer days and shortly thereafter, mortality increased.
Using that method, they found that, of the 35 countries investigated, Italy, Spain, Germany, France, the U.K., and Greece recorded the highest number of heat-related deaths during the summer of 2022. Most of these deaths occurred during a five-week heat wave from mid-July to mid-August. By comparison, there were around 40,000 heat-related deaths in Europe in 2018 and 2019, and 33,000 in 2020.
Read more: How Extreme Heat Impacts Your Brain and Mental Health
How is heat contributing to more deaths? Ballester says heat basically becomes an added risk factor for people with existing health problems, including heart and immune conditions. Heat acts as a stressor on those already precarious systems, for example, by placing further burden on the heart as it tries to pump harder to push more blood to the extremities and skin in an attempt to cool the body’s core. If external temperatures are too high, then “the physiological limit of the cardiovascular system is exceeded,” says Ballester.
The study also found some interesting differences based on age and gender. Heat-related deaths were higher among men than women through age 64, but the gender difference reversed among the elderly, with more women than men dying of heat-related issues. That may be related to the fact that men tend to experience heart-related events, including deaths, at earlier ages than women, so may have died before making it to older age.
The group also found that in all age and sex groups, countries in the Mediterranean—Italy, Greece, Spain, and Portugal—recorded higher mortality rates than countries in central or northern Europe. Social and economic factors such as the robustness of the health care infrastructure and the design of cities, including the amount of green spaces urban areas contain, could account for some of those differences.
Read more on extreme heat:
- The art of air conditioner maintenance
- How to sleep when it’s really hot outside
- Why extreme heat is so bad for the human body
- How to build up your heat tolerance for a hotter world
Ballester hopes the data raise awareness of how much heat is impacting health in the world, and appreciation of the urgency of bringing heat-related deaths down. “They are preventable,” he says. “One way to deal with the effects of heat is to improve the health conditions that make people more vulnerable to heat’s effects—improving the cardiovascular health of people, especially the elderly, will automatically turn into an improvement in our prevention efforts on the effects of heat. Better investment in everything that protects people from getting ill will lead to reducing deaths from heat.”
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