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New research conducted at the state level provides evidence that exposure to extreme heat is linked to a higher prevalence of depression and anxiety across the United States. The findings suggest that as the number of days with temperatures exceeding 100 degrees Fahrenheit increases, the rates of reported mental health issues also tend to rise. This study was published in the Journal of Psychiatric Research.
“We were motivated to conduct this study because we both have an interest in the topic of climate change,” said study authors Dale Pendleton, a clinical resource coordinator at Rush University Medical Center and Aneta Kwak, a manager of division operations at the Ann & Robert H. Lurie Children’s Hospital of Chicago.
“During the period of choosing a topic, California just experienced significant wildfires and most of the United States just finished an extreme polar vortex so climate change was a relevant topic. We also had a strong interest of weather and climate change prior for many years.”
“Nevertheless, our current presidential cabinet has expressed the debate about whether climate change does exist. With these issues at hand, we were eager to dive into the issue of climate change. We also expressed interest in the topic of mental health, from previous classes that covered topics of mental health. With that said we decided to combine the study of mental health and climate change.”
To investigate this relationship, the research team employed a lagged cross-sectional design. They utilized publicly available data from several federal sources, including the Centers for Disease Control and Prevention and the U.S. Census Bureau. The study focused on creating a clear picture of environmental exposure and subsequent health outcomes.
The researchers measured extreme heat exposure by calculating the average number of days where temperatures exceeded 100 degrees Fahrenheit. This data was collected for the period between June and September of 2020. They chose this specific timeframe to capture the peak summer months when heat exposure is most acute.
This environmental data was then compared against mental health data collected in 2022. Using a two-year lag allowed the researchers to look for potential delayed or lingering effects of environmental stress on the population.
The primary measure for mental health was the prevalence rate of depression and anxiety within each state. To ensure the results were not skewed by other factors, the researchers controlled for several key demographic variables.
These included the percentage of the population aged 65 or older and the gender distribution within the state. They also accounted for racial and ethnic composition, specifically looking at the percentages of residents identifying as White, Hispanic, African American, or other races.
Socioeconomic factors were also a major component of the analysis. The team included data on educational attainment, defined as the percentage of the population with a high school education or less.
They also included the percentage of individuals without health insurance. By adjusting for these variables, the researchers aimed to isolate the specific relationship between heat and mental health. The final sample included data from all 50 U.S. states.
The analysis revealed a positive association between the number of extreme heat days and the prevalence of mental health issues. States that experienced more days over 100 degrees Fahrenheit in 2020 reported higher rates of anxiety and depression in 2022. This relationship held true even after the researchers adjusted for the demographic and socioeconomic factors.
The study provides specific estimates regarding the magnitude of this effect. The data indicates that for every additional 10 days of extreme heat, there was a 6.2 percent increase in the odds of reporting mental health issues. While this percentage might seem modest at first glance, the authors note that it represents a meaningful shift when applied to the entire population of a state.
Descriptive statistics from the study show the scale of the issue. The median prevalence of mental health conditions across the states was 51 percent. The median number of extreme heat days was approximately eight. However, there was significant variation between states, which allowed the researchers to detect the underlying pattern connecting heat to health outcomes.
“Climate change is a very real event that does impact many people global, especially impacting mental health such as in forms of anxiety and depression,” Pendleton and Kwak told PsyPost. “Our study highlights the escalating public health concerns associated with climate change by revealing a substantial correlation between extreme heat events and detrimental mental health outcomes across all 50 U.S. states.”
“Notably, increased exposure to extreme heat at the state level was significantly linked to higher prevalence rates of mental health issues, particularly anxiety and depression. Our study findings are consistent with prior research highlighting the negative impact of extreme heat exposure on mental health.”
The results also highlighted the role of socioeconomic vulnerability. There was a strong correlation between lower educational attainment and higher rates of mental health issues. Similarly, states with a higher percentage of uninsured residents tended to have higher prevalence rates of depression and anxiety.
“These findings suggest that the mental health impacts of climate-related heat exposure may be significantly worse in states with greater social and structural vulnerability, highlighting the intersection between environmental stressors and inequities in education and access to health insurance,” the researchers explained.
One finding stood out as unexpected to the researchers. The analysis showed that states with a higher proportion of adults aged 65 and older actually had lower odds of reported mental health issues. This contrasts with many assumptions in public health that older adults are universally more vulnerable to the impacts of climate change. The authors suggest this warrants further investigation.
The researchers also examined correlations with race and ethnicity. The data showed that a higher percentage of residents identifying as “other races” was negatively correlated with mental health prevalence. Meanwhile, the relationships between other racial groups and mental health outcomes were less consistent once other variables were controlled.
It is important to consider certain limitations when interpreting these findings. The mental health data was collected in 2022, a time when the United States was still dealing with the societal and psychological aftershocks of the COVID-19 pandemic.
“A key caveat is that the elevated prevalence of mental health issues observed in 2022 may partly reflect the lingering psychological and social impacts of the COVID-19 pandemic, rather than climate-related heat exposure alone,” the researchers noted. “Readers should therefore avoid interpreting the observed associations as solely attributable to extreme heat, as pandemic-related stressors and disruptions in access to care may have contributed to mental health outcomes during this period.”
Additionally, the study utilized state-level data. This approach provides a broad overview but cannot capture the nuance of individual experiences. The researchers were unable to control for every potential confounding variable, such as access to mental healthcare facilities, population density, or local policies designed to help residents adapt to the heat.
Despite these limitations, the study offers evidence that climate change is a multifaceted threat to public well-being. The findings indicate that the warming climate may act as a threat multiplier, worsening existing health disparities. The authors argue that these results demonstrate the need for comprehensive strategies to address the mental health impacts of extreme weather.
“Our future research could extend this work by focusing on single state or local level analyses and by examining the mental health impacts of other climate-related disasters such as wildfires or floods,” Pendleton and Kwak said. “We would focus heavily on the role of insurance coverage and access to mental health care. Comparing different types of extreme events could help determine whether certain disasters pose greater mental health risks and whether existing health systems and insurance structures are equally effective in responding across event types.
“We would like to emphasize that this study underscores the importance of expanding climate change related health research, because the health consequences of climate change remain underrecognized particularly for mental health. Climate change represents a fundamental threat to human health with implications not only for individuals, but also for the sustainability and resilience of health care systems. By focusing on the association between environmental exposures and social vulnerability, this work emphasizes the need for expanded research to inform public health planning and policy responses.”
The study, “Mental health impacts of extreme heat exposure in the United States: Results from a state-level analysis,” was authored by Aneta Kwak, Dale Pendleton, and Chien-Ching Li.
