As the United States recovers from its 4 July heatwave, a new study warns that prolonged extreme heat may increase hospitalisations for mental health and behavioural disorders. Published in Nature Health, the research is the first multi-country study to examine heatwave-related mental health hospitalisations and was led by researchers at Monash University in Australia.
Led by Professors Yuming Guo and Shanshan Li, the study analysed more than 2.6 million warm-season hospitalisations across 852 locations in Brazil, Canada, Chile and New Zealand between 2000 and 2019. The researchers found that sustained exposure to extreme heat during heatwaves was associated with a higher risk of hospitalisation for mental and behavioural disorders. Heatwaves are generally defined as periods of extremely high temperatures lasting several days, when heat-related illness and deaths can rise substantially.
The association between heatwave exposure and mental health-related hospitalisation was particularly pronounced among older adults and people living in areas with low population density. According to Guo, the findings suggest that prolonged extreme heat can rapidly increase demand for hospital care related to mental health. The results highlight the need for targeted health system preparedness and support for vulnerable populations during periods of severe and sustained heat.
Li said climate change has become an increasingly important influence on mental health worldwide. Extreme weather events, shortages of essential resources and disruptions to ecosystems can intensify psychological stress and increase mental health risks. Of particular concern is the growing frequency and intensity of heatwaves, including extreme heat events recently experienced in the United States and across Europe. As global temperatures rise, researchers are increasingly examining how climate-related hazards affect not only physical health but also psychological and behavioural well-being.
Several factors may explain the relationship between heatwaves and mental health hospitalisations. Extreme heat can disrupt sleep and trigger physiological stress responses, potentially worsening existing mental and behavioural disorders. People with impaired ability to regulate body temperature may be especially vulnerable, as may individuals taking medications that increase sensitivity to heat. Heat-related psychological distress and changes in behaviour may also destabilise symptoms, contributing to a greater need for hospital care during or following prolonged periods of extreme temperatures.
The study is the first to estimate the risks and hospital burden associated with heatwave-related mental and behavioural disorders across multiple countries and population groups. Researchers examined differences by sex, age, GDP per capita, population density, air-conditioning access, travel time to healthcare facilities and specific causes of mental and behavioural disorders. The findings provide new evidence of the mental health consequences of extreme heat and suggest that healthcare systems may need to strengthen preparedness as heatwaves become more frequent and intense under climate change.
More information: Yanming Liu et al, Mental health hospitalizations associated with sustained extreme heat in multiple countries, Nature Health. DOI: 10.1038/s44360-026-00166-2
Journal information: Nature Health Provided by Monash University
