Waves of extreme heat, which are on the rise due to climate change, are linked to an uptick in emergency room visits for mental health conditions, a new study has determined.
On such hotter-than-normal days over the past decade, emergency department check-ins for any mental health condition surged by 8 percent in comparison to days of optimal temperature, according to the scientists, who shared their results on Wednesday in the journal JAMA Psychiatry.
The authors also identified robust connections between such temperatures and emergency room (ER) visits for specific mental health conditions, including substance use disorders; anxiety- and stress-related disorders; mood disorders; self-harm; childhood-onset behavioral disorders and schizophrenia, schizotypal and delusional disorders.
“Days of extreme heat can profoundly affect our physical and mental health,” lead author Amruta Nori-Sarma, an assistant professor of environmental health at the Boston University School of Public Health, told The Hill in an email.
While the implications of extreme heat for physical ailments have been well documented, the potential connection between elevated temperatures and mental health issues remains poorly understood, according to the authors.
Seven of the warmest-ever years in contiguous U.S. history have occurred since 2014, with 2016 topping the charts and 2020 ranking as the second warmest year in the 141-year record available, the study said. Heat stress, the authors explained, is known to trigger adverse physiological reactions in the body, and exposure is associated with increased morbidity and mortality.
“Climate change poses an unprecedented threat to human health,” Nick Obradovich, of the Max Planck Institute for Human Development, and Kelton Minor, of the University of Copenhagen, wrote in a JAMA editorial accompanying the study.
“Among the myriad likely human impacts of climate change, the potential for environmental stressors to undermine global mental health and emotional well-being is one of the most considerable,” the editorial added.
Although an increasing number of studies have reported possible adverse consequences of heat on mental health, this research has been limited to small sample sizes or specific populations, according to the study.
“Thus far the collective scientific and clinical knowledge is sparse relative to the specter of the coming threat climate change poses to human mental health,” the JAMA editorial stated. “Ever-more mental health scientists and clinicians are needed to work on this topic.”
To draw their conclusions, the scientists analyzed a pool of 3.4 million emergency department visits among 2.2 million adults in the contiguous U.S. during warm season months — May to September — from 2010 in 2019. About 57 percent of these individuals were women, with a median age of 51 years old.
Looking at links between extreme heat and emergency department visits for any type of mental health condition, the authors calculated an “incidence rate ratio” of 1.08 in comparison to a baseline of 1.0. This meant that mental health visits to the ER of any type experienced an 8-percent increase on such days.
For substance use disorders specifically, the ratio was also 1.08, while for anxiety and stress-related disorders it was 1.07; mood disorders were 1.07; self-harm was 1.06; childhood-onset behavioral disorders it was 1.11 and for schizophrenia, schizotypal and delusional disorders it was 1.05.
While associations were higher in men than in women, the authors found no evidence of differential links according to age groups, which they said contrasted previous findings.
The scientists also said they observed higher rates of mental health-related ER visits during heat waves in the Northeast, Midwest and Northwest regions of the U.S. This observation, they concluded, could suggest “an increased risk of adverse mental health outcomes in regions of the U.S. that are less well adapted to heat,” or where air conditioning may be less common.
Some factors that might lead to a surge in visits include heat’s role as an external stressor, its ability to disrupt sleep, resultant daytime discomfort and an increase in hopelessness or maladaptive anxiety, the authors conjectured.
The emergency room, which might be the only healthcare facility open during heat-related shutdowns, could also provide patients with relief from hot weather, according to the study.
The connection between heat and ER visits across a variety of mental health outcomes demonstrates that this external stressor is not likely specific to any one condition, Nori-Sarma explained.
“Rather, we think of it as exacerbating existing mental health conditions,” she said.
While the authors described their study as “filling an important gap in existing literature,” they also acknowledged its limitations.
For example, the scientists said that they did not consider meteorological conditions aside from heat, such as precipitation or cloud cover, which could also alter mental health. Data providing individual-level characteristics like race and ethnicity, socioeconomic means and occupation was not available, while the focus on ER visits meant focusing on severe mental health presentations only, the authors added.
In addition, the scientists said they could only access data on individuals who have commercial health insurance or Medicare Advantage, meaning that many lower-income patients could not be included. This absence may have led to a “skewing of the sample toward wealthier socioeconomic status” and could limit the generalizability of the study, according to the authors.
“We do think that our study is an underestimate of the actual burden of high temperature on mental health since we rely on data among insured individuals, and we are missing the potentially very vulnerable population of uninsured individuals,” Nori-Sarma told The Hill.
Accessing information on such vulnerable communities would be difficult by the methods the authors used in this study, which explored expansive datasets across the U.S., she said.
What might be more feasible, she suggested, would be “to rely on highly local work looking at climate impacts on mental health outcomes within those communities and done in collaboration with those communities.”
With the currently available data, however, Nori-Sarma said that clinicians and public health experts could make use of their study to prepare additional outreach to patients who have existing mental health conditions, when heat wave forecasts come up.
“Our findings indicate that the needs for mental health services may be especially high during times when extreme heat is being predicted, giving us a leg up on preparing the healthcare system to address those needs,” Nori-Sarma added.