Higher temperatures linked to an increase in suicidal thoughts and behavior

Scientists have linked warmer temperatures to an increase in suicidal thoughts and behavior in young people. The new study adds to existing evidence that rising temperatures are also affecting the mental health of adult men and women.

There are many well-known risk factors associated with suicide and youth suicide: recent or serious loss, such as the death of a parent; stressful life events such as abuse; mental illness, especially a mood disorder such as depression; trauma; and problems related to substance abuse.

But new research from the University of New South Wales (UNSW) in Sydney has added another risk factor. A link was found between an increase in suicidal thoughts and behaviors in adolescents and higher temperatures.

Researchers examined 55,000 emergency department calls for suicide in people aged 12 to 24 across the state of New South Wales during Australia’s warmer months (November to March) between 2012 and 2019.

When they compared this data with daily mean temperature (DMT) and heat waves, they found that the incidence of youth suicide with ED was significantly higher on warmer days. The relationship was linear: for every 1°C (1.8°F) increase in DMT ED use, young people’s emergency room visits due to suicidal thoughts or behavior increased by 1.3%.

“The impact on the first day, when the temperature is higher than usual, is as severe as on any subsequent day, and the effect begins at a more moderate temperature than expected,” said Dr Cybele Dey, a psychiatrist and lecturer at UNSW Sydney and leader of the study and corresponding author.

For example, on days when the average 24-hour temperature was 21.9°C (71.4°F), which was the average DMT during the study period, there was an average of 45.7 cases of youth suicide reported statewide. At this temperature, presentations were 4.7% higher than normal with the state’s average spring DMT being a cooler 18.3°C (64.9°F).

When DMT temperatures rose to 25.2°C (77.4°F), the baseline level for the heat wave, DMT levels were about 9% higher than in the spring. By the time DMT reached its “extreme temperature” of 30 °C (86 °F), the content of the substance was approximately 15% higher.

“There was an increase in cases on the first moderately hot day, which tells us this is a biological effect rather than a side effect of factors such as poor sleep,” Dey said. “It appears that heat itself increases people’s anxiety, which is supported by other literature. We know that the number of mental health emergency calls increases with temperature, and there are foreign studies showing a link between exposure to heat and the occurrence of suicidal thoughts, but also increased temperature and death by suicide.

IN August 2024research led by Curtin University found that over almost 20 years, about 0.5% of suicide deaths in Australia – 264 people – were correlated with unusually higher temperatures caused by climate change. Suicides related to thermal anomalies were statistically significant among men aged 55 years and older. Seasonality was an important factor, with more deaths in spring (September to the end of November) and summer (December to the end of February).

A few months earlier, in AprilResearch from the University of Sydney has found a link between higher temperatures and mental health in Sydney Hospital, particularly for women whose risk increased significantly at temperatures of 29.2°C (84.6°F) or above.

Researchers in the current study found that socioeconomic disadvantage related to poorer housing quality and the ownership and use of air conditioners, as well as more limited access to green spaces and waterways, are important issues.

“Independent access to green spaces, nighttime cooling from the sea breeze and the quality of housing are important factors in determining how people cope with the heat,” said Dr Iain Perkes, a psychiatrist and senior lecturer at the UNSW School of Clinical Medicine and co-corresponding author of the study. “We will need to do more research on these possible mediating factors, but that shouldn’t stop us from continuing our work and making sensible changes that we know work more broadly to reduce exposure to higher temperatures.”

They said improving the quality of housing and ensuring young people have access to cool environments at home and at school will help them better protect them from the mental health effects of higher temperatures.

“Public health messages about heat tend to be limited to heat waves and focus on the very young and the elderly,” Dey said. “However, we must do more to warn and protect the entire population from the impact of this situation on their physical and mental health.”

Doctors for Environment Australia (DEA), a medical group calling for climate action to reduce health damage, called for an urgent phase-out of fossil fuels based on the study’s findings.

“Our research shows that the mental health of young Australians is suffering due to heat and we know that climate pollution is contributing to the increase in extreme weather, including heat,” said DEA spokesman James Scott, professor of child and adolescent psychiatry and co-author of the study: “ To reduce the harmful mental health effects of heat on children and young people and reduce cases of erectile dysfunction, we need an urgent and rapid transition from fossil fuels to clean energy.”

More research is needed on the link between youth mental health and heat to confirm whether warmer temperatures are causing the increase or are simply a coincidence.

“It’s pretty amazing,” Perkes said. “While we have not established causality here, the type of pattern … would indicate a cause-and-effect response.”

The study was published in the journal Australia and New Zealand Journal of Psychiatry.

Sources: UNSW Sydney, DEA