Heat raises risk of youth suicide

Hotter days increase distress in the young, while older people need more than electric fans to stay cool.

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The risk for youth suicidality increases with every degree, a new Australian study finds.

Presentations of suicidal thoughts and behaviours in NSW emergency departments increased by 1.3% for young people aged 15-24 with every degree the temperature rose above the daily mean, according to researchers from UNSW, Sydney Children’s Hospitals Network, NSW Ministry of Health, NSW Health, University of Sydney and Queensland Children’s Hospital.

“For instance, on days with a DMT [daily mean temperature] of 26.9°C, the relative risk was 1.065, whereas on days with a DMT of 16.9°C, the relative risk was 0.94,” the authors, explained.

Or to demonstrate it another way, there were 11% more presentations on days with a DMT of 30C than there were on days with DMT of 21.9C, they say.

“The impact on the very first day where the temperature is hotter than usual is just as bad as each subsequent day, and the effect starts at a more moderate temperature than expected,” lead author Dr Cybele Dey, a psychiatrist and conjoint lecturer at UNSW Sydney, told media.

“This is not about concern about climate change affecting the mental health of young people, this is about hot weather itself affecting them.”

A relationship between temperature and presentations was seen whether it was a single hot day, or a heatwave, and across climate zones and demographic groups. But it was weakest in the coastal regions, including eastern Sydney. These are areas of higher economic advantage, with access to air conditioning and better housing, the authors note.

Young people work outside, play sport outside, and often have less money, all putting them at increased risk of being affected by the heat, the paper says.

Suicide is the leading cause of death for young Australians. Youth suicidality presentations at NSW emergency departments went up 8.4% every year from 2015 to 2020.

The researchers from looked at presentations at emergency departments from 2012 to 2019 for suicidality by people aged 12-24 across different climate zones in the state, during the period of November to March each year. They also looked at the corresponding mean daily temperatures and heat waves.

The mean daily temperature across the state was 21.9C, ranging from 18.7C in the cool temperate climate zone to 24.4C in the hot dry zone. The hottest single point temperature was 49.1C and the highest mean temperature was 35.3C, occurring in the hot dry zone.

“Across climate zones, increases in DMT were predominantly associated with increased risk of suicidality presentations,” the authors write. The association was most evident in the hot dry, mild temperate and cool temperate zones.

Dr Dey told media that the mechanism could be biological.

“There was an increase on the first moderate hot day, which tells us it is more likely to be a biological effect, rather than a flow-on effect from factors like poor sleep,” he said.

“The heat itself looks to be doing something to increase people’s distress and that is supported by other literature. We know that calls to mental health crisis lines go up with temperature and there are overseas studies showing a link between heat exposure and suicidality presentations.”

At the other end of the age spectrum, a Canadian study has shown that electric fans don’t cut it when it comes to older people coping with high temperatures indoors.

In a randomised control trial, 18 participants aged 65-85 were exposed to three eight-hour sessions of 36C heat and 45% relative humidity, while sitting in front of a fan – either turned off, at normal air speed, or at high speed.

Their mean core temperature remained at 38.3C, with and without the fan. There was also no significant difference in blood pressure, rate pressure product, plasma volume change, or fluid loss or consumption.

“Consistent with recent modeling, these data do not support fans as an efficacious standalone cooling intervention for older adults in hot indoor environments (>33-35C),” the authors concluded.

Australian & New Zealand Journal of Psychiatry, 23 October 2024

JAMA Network, 17 October 2024