Are high temperatures associated with an increase in suicides?

Europe 1 with AFP 1:59 p.m., August 24, 2022

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.

The same phenomena over a period of almost 50 years

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.

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 curve.

Low serotonin may increase risk of acting out

A notable exception is suicide mortality.

"This increases regularly with temperature, but there are no excess suicides with cold temperatures," Rémy Slama, head of the study and director of research at Inserm, told AFP.

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 suicide," explains Rémy Slama.

Changing social interactions could influence

Another hypothesis: "the modification of social interactions, reduced in periods of high heat, could influence certain passages to the act", he advances.

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.

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, undoubtedly thanks to changes made in health systems or habitat", underlined Mr. Slama.

"But this has its limits and cannot completely erase the impact of rising temperatures".