Extreme heat and polluted air may together increase the risk of suicide, according to a new study that highlights how environmental factors could influence mental health in ways scientists are only beginning to understand.
Researchers from the University of Utah Health and the Huntsman Mental Health Institute analysed more than 7,500 suicide cases in the US state of Utah between 2000 and 2016.
Their findings, published in the journal Environment International, suggest that high temperatures combined with certain types of air pollution can significantly amplify suicide risk.
Scientists have long known that suicide rates in the United States have been rising since the late 1990s. Previous research has linked both heat and poor air quality individually to short-term increases in suicide risk. However, the new study examined how these factors interact with each other.
“The two-week period just before suicide is a critical time for intervention,” said Amanda Bakian, a psychiatry researcher at the University of Utah Health and senior author of the study. “Many environmental factors have been associated with short-term suicide risk, but very little has been done to consider what’s happening when they occur together.”
To better measure the effects of heat, the researchers used the Wet Bulb Globe Temperature, which incorporates temperature, humidity, wind speed and cloud cover to estimate how heat actually feels to the human body.
The analysis showed that heat exposure was linked to a higher suicide risk. For every 9°F increase in wet bulb globe temperature, suicide risk rose by about five per cent. The association was strongest during the warmer months, between late March and late September.
The study also examined levels of Nitrogen Dioxide, a gas commonly produced by vehicles and fossil-fuel power plants. Researchers found that while nitrogen dioxide alone did not significantly increase suicide risk during warm months, it dramatically intensified the impact of heat.
During the warm season, when nitrogen dioxide levels were high, each 9°F increase in heat stress was associated with nearly a 50 per cent increase in suicide risk.
In colder months, when pollution tends to accumulate in the atmosphere, higher nitrogen dioxide levels were linked to increased suicide risk regardless of temperature.
Scientists caution that the findings show correlations rather than direct cause-and-effect relationships. However, the results raise important questions about how environmental conditions may influence mental health.
Researchers say climate change, increasing heat waves, and changing pollution patterns could alter these risks in the future. They also plan to explore how genetic factors might interact with environmental stressors to identify people who may be most vulnerable.
The findings suggest that environmental policies aimed at reducing air pollution and extreme heat exposure could play a role in suicide prevention, potentially enabling earlier warnings and targeted interventions during high-risk periods.
