- A new study links extreme heat to more hospitalizations for mental and behavioral disorders.
- The first multi-country study of its kind used records from 2.6 million hospitalizations.
- Hot weather drives irritability, impulsivity, depression, psychotic episodes and increased crime.
If historical patterns hold true, the parts of the U.S. that have been under a heat dome recently can expect to see more hospital visits for behavioral and mental health disorders, according to a new, peer-reviewed international study.
Published in Nature Health, the researchers looked at more than 2.6 million warm-season hospitalizations from 852 locations in Brazil, Canada, Chile and New Zealand between 2000 and 2019. And they concluded that the link is real and is especially “pronounced among older adults and residents of low-population-density areas,” according to a news release from Monash University in Australia.
Heat waves are “increasing in frequency and intensity,” per the study, which defined a heat wave as a period with daily mean temperatures above the location-specific 97.5th percentile for at least four consecutive days.
The findings “indicate that prolonged extreme heat can acutely increase mental health-related hospital demand and support targeted preparedness during severe heat waves,” the authors wrote.
The release specifically called out intense high temperatures this month in the United States and Europe.
Researchers found the high temperatures over time “may trigger acute exacerbations of mental and behavioral disorders through sleep disruption and physiological stress responses, with heightened vulnerability among individuals with impaired thermoregulation or medication-related heat sensitivity.”
It’s well-known that as people get older, their bodies may not regulate their internal temperatures as well as they did when someone was younger. And older adults are also more likely to be on medications, including those that can make someone sensitive to heat, which could account for the finding that older adults are at elevated risk.
The researchers said this study is the first to estimate heat-wave-related hospitalization and “burdens for mental health and behavioral disorders across different countries, sex, ages, GDP per capita, population densities, air-conditioner penetrations, travel time to healthcare facilities and causes of mental health and behavior disorders.”
Heat and the brain
The American Psychological Association in 2024 published a journal cover story on the impact heat has on mental health. The article noted an “urgent” need for policy and infrastructure changes to protect mental health.
While physical consequences of extreme heat are well-known — including dehydration, heat exhaustion, heat stroke and even death at the more extreme ends — psychological consequences are less so. They range, the article said, “from irritability to impulsivity to trouble concentrating. The impacts can put already-vulnerable people in crisis during heat waves but may also lead to general mental health impacts and increased friction within society.”
The article cites a study that says young people are especially at risk “given the potential impact of heat-related mental health effects on developing brains.”
“Extreme heat can make people more depressed or irritable, it can bring on psychotic outbreaks, and people on certain psychiatric medications are more sensitive to heat,” Jane Gilbert, the world’s first chief heat officer, a government position established in 2021 in Miami-Dade County, told the association.
A 2022 study published in JAMA Psychiatry found that mental health conditions made worse by extreme heat include anxiety and stress-related disorders, mood disorders, schizophrenia and delusional disorders, substance use disorders, self-harm and behavior issues in children. And since that only includes those noted in emergency department visits, there are likely others, the authors said.
The association article also notes long-held findings that high temperatures and criminal justice issues are linked, including an increase in both robberies and aggravated assaults, with an even greater increase in homicides compared to days with more normal temperatures.
“For local governments, heat mitigation is one of the primary ways to attempt to soften the psychological impacts of heat. When you cool down a neighborhood, it benefits your physical and your emotional health,” Ali Frazzini, a policy adviser with a background in public health at the L.A. County Chief Sustainability Office, was quoted in the article.