High temperatures are associated with a general increase in short-term deaths, and more specifically suicides, underlines this Wednesday a study by the National Institute of Health and Medical Research (Inserm), which confirms the results of previous scientific publications.
Studies carried out in the United States and Mexico have already revealed an excess of mortality, both in the coldest and warmest periods. They have also established a specific link between the increase in suicides and high temperatures, which does not occur in cold weather.
In the new study, published this week in the American Journal of Epidemiology, Inserm researchers observed the same phenomena over a period of almost 50 years in France.
Suicide mortality increases above 20°C
The scientists compared the number of deaths occurring each day since 1968 in each region with daily temperatures over the entire observation period, looking only at short-term links between temperature and mortality.
The mortality rate was minimal when the temperature was close to 20°C. It increased both when the temperature exceeded 20°C and when it fell below 20°C. Among the 22 causes of death considered, almost all followed this U-curve.
A notable exception is suicide mortality. “This increases regularly with temperature, but there is no excess of suicides with cold temperatures,” Rémy Slama, head of the study and director of research at Inserm, told AFP.
Decreased serotonin and social interactions among possible explanations
If the study does not delve into the biological parameters that would make it possible to understand the underlying mechanisms that explain this link between temperature and suicide, some hypotheses can be proposed.
“Increasing temperatures are known to reduce the levels of the hormone serotonin, which has an inhibitory function of impulsive behavior: its decrease could increase the risk of committing suicidal acts”, explains Rémy Slama.
Another hypothesis: “the modification of social interactions, reduced in periods of great heat, could influence certain passages to the act”, he advances.
Dimming during certain periods
This research also aimed to see if the impact of temperatures varied over time, isolating three different periods. It shows that the effects of temperature on all-cause mortality and suicide mortality decreased between the periods 1968-1984 and 1985-2000.
However, no new attenuation was observed during the 2001-2016 period compared to the previous period (1985-2000).
“This advocates a certain adaptation of society to extreme temperatures, no doubt thanks to the changes made in the health or housing systems”, emphasizes Rémy Slama. “But this has its limits and cannot completely erase the impact of rising temperatures.”
Source: BFM TV
