Does Extreme Heat Prompt More Mental Health-Related ED Visits?

The hottest days on record over the last decade were linked with increased mental health-related emergency department (ED) visits among U.S. adults, a large case-crossover study found.

Using medical claims data from 2010 to 2019, extreme heat days -- the 95th percentile for warm-season temperature distribution -- were associated with a modestly higher rate of ED visits for any mental health condition (incidence rate ratio [IRR] 1.08, 95% CI 1.07-1.09), reported Amruta Nori-Sarma, PhD, MPH, of Boston University School of Public Health, and colleagues.

Writing in JAMA Psychiatry, this association was significant for a range of specific mental health conditions:

• Substance use disorders: IRR 1.08 (95% CI 1.07-1.10)
• Anxiety, stress-related, and somatoform disorders: IRR 1.07 (95% CI 1.05-1.09)
• Mood disorders: IRR 1.07 (95% CI 1.05-1.09)
• Schizophrenia, schizotypal, and delusional disorders: IRR 1.05 (95% CI 1.03-1.07)
• Self-harm: IRR 1.06 (95% CI 1.01-1.12)
• Childhood-onset behavioral disorders: IRR 1.11 (95% CI 1.05-1.18)

"Our finding that heat was associated with a similar increase in the rate of ED visits for a variety of different mental health conditions is consistent with the hypothesis that heat is an external stressor that is not specific to any given mental health condition," Nori-Sarma's group wrote. "One etiological mechanism may be disrupted sleep during periods of high ambient temperature, which may be associated with adverse mental health outcomes."

Men appeared to be at higher risk (IRR 1.10, 95% CI 1.08-1.12) as were those living in the Northeast, Midwest, and Northwest regions of the U.S.

The regional findings suggest there is an elevated risk of adverse mental health outcomes in areas less accustomed to hot temperatures compared with historically hot geographical regions.

However, hot temperatures may not be the only threat to mental health, Nick Obradovich, PhD, of Max Planck Institute for Human Development in Germany, and Kelton Minor, MS, of the University of Copenhagen in Denmark, warned in an accompanying editorial.

While the current study does exhaustively highlight the impact that heat can have on a wide range of mental health conditions, the researchers' focus on high temperatures is limiting. This focus on heat, rather than cold temperatures, is an "all-too-common," albeit problematic practice in research.

"Researchers should consider the full distribution of temperature -- and a full suite of other potentially confounding meteorological variables -- in their analyses," the editorialists wrote. "After all, understanding the net effect of temperature change across the shifting distribution of temperature (climate change will produce warming across all seasons) is of great importance to understanding the consequences of climate change for mental health in the future."

In their article, Nori-Sarma's group did point out that while mental health consequences surely arise due to extremely cold temperatures, these adverse outcomes may affect health on a different time scale "with substantially longer lag effects during cold periods compared with hot periods."

Another limitation Obradovich and Minor highlighted was the use of clinical diagnoses to evaluate the impact of climate change on mental health. "Although some work has been done on day-to-day emotional states and self-reported mental health status, the frontier in such empirical work remains understanding what climatic stressors do to the mental health of the large percentage of the population that will rarely show up in clinical or hospital settings," they wrote.

For the analysis, the researchers gathered county-specific daily maximum ambient temperature data from May through September using the Parameter-Elevation Regressions on Independent Slopes (PRISM) model from the PRISM Climate Group.

Claims for adults with commercial health insurance or Medicare Advantage from 2,775 U.S. counties were included in the analysis. Overall, Nori-Sarma's group identified data from 3,496,762 ED visits among 2,243,395 individuals. The study sample had a mean age of 51 years and 56.8% of the population identified as women.

Based on their results, Nori-Sarma's group recommended that mental health clinicians and emergency health practitioners should consider increasing capacity to provide necessary care during and after periods of extreme heat.

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