Do Heatwaves Cause More Mental Health Hospitalizations?

A new study published in the Journal of Nature Health looked at whether mental health hospitalizations were associated with sustained extreme heat in multiple countries.

“Our study investigated whether heatwaves are associated with an increased risk of hospitalization for mental and behavioural disorders,” study author Yanming Liu told us. “Although the physical health effects of extreme heat are well established, its effects on mental health have received less attention, particularly across different countries and populations. We wanted to understand whether prolonged periods of extreme heat increase demand for mental health-related hospital care, and whether some population groups or communities are more vulnerable than others.”

The researchers expected that exposure to heatwaves would be associated with a higher risk of hospitalization for mental and behavioural disorders. They also expected that more intense and longer-lasting heatwaves would have stronger effects, because sustained exposure gives the body and mind less opportunity to recover. In addition, the researchers anticipated that certain groups, including older adults and people living in communities with fewer resources or less access to health services, might be more vulnerable.

“Heatwaves are becoming more frequent, intense and prolonged due to climate change, but their mental health consequences remain comparatively understudied,” Liu told us. “Most heat-health research has focused on outcomes such as cardiovascular disease, respiratory illness and mortality. However, extreme heat can also affect sleep, emotional regulation, medication responses, social behaviour and the management of existing mental health conditions. We felt it was important to quantify this burden using large-scale health data, particularly because mental health services are already under considerable pressure in many countries.”

The research team analyzed over 2.6 million warm-season hospitalizations for mental and behavioural disorders across 852 communities in Brazil, Canada, Chile and New Zealand between 2000 and 2019. They used a case-crossover study design, which compares the temperature conditions immediately before a person’s hospitalization with temperature conditions during other comparable periods for the same person. This approach helps control for individual characteristics that do not change over a short period.

“We tested several definitions of a heatwave, using different temperature thresholds and durations, and examined both immediate and delayed effects over the following days,” Liu told us. “We also assessed whether the associations differed by age, sex, diagnosis and community characteristics.”

The researchers found that exposure to heatwaves was associated with an increased risk of hospitalization for mental and behavioural disorders. The effects were generally stronger when heatwaves were more intense or lasted longer. Under one of the most extreme heatwave definitions, temperatures above the 97.5th percentile for at least four consecutive days, the cumulative risk of hospitalization increased by approximately 5.6% on the day of exposure and over the following eight days.

“We also found that the association was more pronounced among older adults and among people living in lower-population-density communities,” Liu told us. “Some specific categories of mental and behavioural disorders also appeared to be particularly sensitive to extreme heat. Overall, we estimated that heatwaves accounted for around 3% of warm-season hospitalizations for mental and behavioural disorders across the study locations, although the burden varied between countries and population groups.”

While the overall association was consistent with the research team’s expectations, they found the scale and pattern of vulnerability to be striking.

In particular, the stronger effects among older adults highlighted that heat-related mental health risks may be concentrated among people who already face physiological, social or healthcare-related vulnerabilities. The higher risks in lower-population-density communities were also notable. 

“Although our study could not determine the exact reasons, these areas may have less access to healthcare, cooling infrastructure, public transport or other forms of support during extreme weather,” Liu told us. “We were also struck by how the effects could persist for several days after the heatwave exposure, rather than being limited to the hottest day itself.”

Liu believes the findings suggest that mental health needs to be included more explicitly in heatwave preparedness and climate adaptation planning. Hospitals and mental health services may need to prepare for increased demand during and shortly after severe heatwaves. Heat-health warning systems should consider mental and behavioural disorders alongside more commonly recognized physical health outcomes.

“Targeted support may be particularly important for older adults, people with existing mental health conditions and communities with limited access to healthcare or cooling resources,” Liu told us. “This could include early warnings, medication guidance, welfare checks, access to cooling spaces and better coordination between weather services, public health agencies and mental health providers. More broadly, the results show that climate change is not only a physical health issue. It also has important consequences for mental health and the capacity of healthcare systems.”

Categories: Anxiety , Depression , Health | Tags: heatwave, anxiety, depression