High temperatures are associated with a general increase in short-term deaths, and more specifically suicides, underlines an Inserm study on Wednesday, confirming the results of previous scientific publications.
Studies, carried out in the United States and Mexico, have already highlighted an excess of mortality, both during the coldest periods and the hottest periods.
They have also established a specific link between an increase in suicides and high temperatures, which is not present in cold weather.
Increase in suicide mortality
In the new study, published this week in the
American Journal of Epidemiology
, Inserm researchers observed the same phenomena over a period of nearly 50 years in France.
The scientists cross-referenced the number of deaths occurring each day since 1968 in each region with daily temperatures throughout the observation period, looking only at short-term links between temperature and mortality.
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The mortality rate was minimal when the temperature was close to 20°C.
It increased both when the temperature rose above 20°C and when it decreased below 20°C.
Among the 22 causes of death considered, almost all followed this U-shaped curve. A notable exception is mortality by suicide.
“
This increases regularly with the temperature, but there is no excess suicide with cold temperatures
,” Rémy Slama, head of the study and director of research at Inserm, told AFP.
Multiple causes
If the study does not dig into the biological parameters which would make it possible to understand the underlying mechanisms explaining this link between temperature and suicide, some hypotheses can be raised.
"
Rising temperatures are known to lower levels of the hormone serotonin, which has an inhibiting function of impulsive behavior: its reduction could increase the risk of acting out suicide
", explains Rémy Slama.
Another hypothesis:
"The modification of social interactions, reduced in periods of high heat, could influence certain acts
," he suggests.
This research also aimed to see if the impact of temperatures varied over time, by isolating three different periods.
It shows that the effects of temperature on all-cause mortality and suicide mortality diminished between the periods 1968-1984 and 1985-2000.
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However, no new attenuation was observed during the period 2001-2016 compared to the previous period (1985-2000).
“
This pleads in favor of a certain adaptation of society to extreme temperatures, no doubt thanks to changes made in health systems or housing
”, underlined Mr. Slama.
“
But this has its limits and cannot completely erase the impact of rising temperatures
”.