Heat Exposure and Hospital Admissions for Mental Health Disorders in a Changing Climate

OBJECTIVE: To examine associations between ambient temperature and hospital admissions for mental health disorders among children (aged ≤12 years), adolescents (aged 13-17 years), and young adults (aged 18-24 years) and to project future heat-attributable admissions under various climate change scenarios. METHOD: A case-crossover time series study was conducted using hospital admissions for mental health disorders in New South Wales, Australia (2001-2022). Daily average temperature was the exposure. Conditional logistic regression with lag-distributed nonlinear models was used to examine the association in cold and warm seasons. Relative risk (RR) was determined by comparing risk of high temperature (99th percentile) with the minimum morbidity temperature. Attributable fractions of heat (temperatures above minimum mortality temperature) were estimated, and future heat-attributable admissions were projected under 3 greenhouse gas emission scenarios (1980-2099). RESULTS: Among 719,375 admissions, high temperature was associated with increased admissions: RR 3.03 (95% CI 2.56-3.60) in cold seasons and RR 1.92 (95% CI 1.58-2.34) in warm seasons. Elevated risks were observed for substance use, depressive, anxiety, obsessive-compulsive, adjustment, attention-deficit/hyperactivity, disruptive, and impulse control disorders in both seasons (RR 1.45-5.49) and for schizophrenia, eating disorders, and deliberate self-harm in cold seasons (RR 2.22-5.23), but no effect was observed for manic episode and bipolar disorders in either season. Risks were higher among female patients and young adults in cold seasons and among male patients and children (≤11 years old) in warm seasons, with increasing effects in recent years. Heat accounted for 8.36% of admissions in cold seasons and 2.94% of admissions in warm seasons. By 2090 to 2099, heat-attributable admissions are projected to rise by 6.0%, 7.7%, and 20.8% under low-, medium-, and high-emission scenarios. CONCLUSION: High temperatures were associated with increased hospital admissions for mental health disorders among children and young adults. Climate change is projected to amplify this burden, highlighting the urgent need to prioritize mental health outcomes in climate adaptation and public health strategies.