PARIS, France — “Heat waves are extreme climate events which have a huge impact in all age ranges of a population,” said Sébastien Denys, health, environment, and work director at Public Health France, during a press conference on the impact of hot weather during the summer months on the mortality rate in mainland France.
“Since 2015, heat waves are becoming increasingly widespread across the entire mainland, they’re occurring earlier and earlier, starting from June, and have a significant impact on public health in terms of morbidity and excess deaths,” he added.
A heat wave is a period of at least 3 days when the mean maximum temperatures and the mean minimum temperatures exceed the alert thresholds, which vary by region. The alert thresholds are higher in the south of France than in the north. For example, in the Ile-de-France region, the minimum alert threshold is 21° C (70° F), and the maximum alert threshold is 31° C (88° F). Thus, if the mean nighttime temperature exceeds 21° C and the mean daytime temperature exceeds 31° C over 3 days, a heat wave will be declared in Ile-de-France.
To accurately quantify the part of the mortality rate attributable to heat exposure during the summer, Public Health France developed an original method that allows the mortality rate to be estimated regionally — excluding France’s overseas departments and regions — for all age groups and for people age 75 years and above, separately.
To do this, the researchers used the following three figures: the number of all-cause deaths during the summer (linked to heat but also to atmospheric pollution caused by forest fires, drownings, and even COVID-19), the number of deaths specifically attributable to the heat, and the number of occupational accidents related to hot weather.
During the summer (June 1 to September 15) from 2014 through 2022, the following findings were evident across all regions of mainland France:
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Nearly 33,000 deaths were caused by hot summer weather (over 9 years).
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Around two-thirds of excess deaths were in people age 75 years and older, which, although expected, also means that a third of the deaths occurred in younger age groups.
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Generally, between 1000 and 7000 deaths are caused by heat each year, depending on the weather outlook for that year. The year with the greatest impact was 2022, when there were close to 7000 deaths (including more than 2800 during the heat waves that year).
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Of these deaths, 28% occurred during a heat wave (total deaths occurring up to 3 days after the end of the heat wave), as determined by the heat wave management plan, despite only representing 6% of the days studied, “thus justifying especially stringent monitoring and preventive measures.”
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About 72% of heat-related deaths therefore occur outside heat wave periods (spread over 94% of days).
“There is no breaking point, but the more extreme temperatures become, the more the mortality risk increases, exponentially. There is an accelerated mortality risk when temperatures are very high, especially around the 30° C mark,” said Guillaume Boulanger, head of the department for health, environment, and work at Public Health France.
“So, it’s important, in the current context of climate change, to encourage the public to adapt to the heat throughout the summer months, not just during heat waves,” concluded Boulanger.
People need to be reminded about suitable preventive measures (keeping windows open at night, using a damp cloth to cool yourself down, closing the blinds during the day, placing plants in front of windows, putting ice cubes in front of an air conditioning unit, etc) and be aware of the different ways of staying hydrated. People with medical conditions should seek medical advice, with a view to adapting any ongoing medical treatment.
Overall, Public Health France insists on the need to “adapt towns to hot weather conditions, in particular using the concept of “green towns” by means of revegetation, coatings for buildings that absorb little heat, and the installation of water fountains and bodies of water.
Hyperthermia, or the inability to maintain body temperature at 37° C (98.6° F), is one of the three main risks of hot weather. The symptoms are varied and include hot skin, feeling faint, dizziness, nausea, confusion, and trouble speaking. The risk of hyperthermia mainly affects newborns, young children, and adults who are particularly exposed to the elements (sportspersons or outdoor workers).
Hyponatremia mainly affects elderly people who consume too much water and don’t compensate for this with a varied diet. The nonspecific symptoms include nausea, vomiting, weakness, headache, confusion, and finding water to have a strange taste. It can even cause death.
Dehydration occurs in people who sweat a lot and who don’t drink enough. This most often affects elderly people.
This article was translated from the Medscape French Edition.
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