Extended heat waves linked to higher mental-health hospitalizations across four countries

Using a time-stratified case-crossover analysis of 2,618,307 warm-season hospitalization records from 852 locations in Brazil, Canada, Chile and New Zealand (2000–2019), the study finds sustained extreme heat defined as four consecutive days above the local 97.5th percentile increases mental and behavioral disorder hospitalizations on the exposure day (RR 1.033) and cumulatively over the next 8 days (RR 1.056), with stronger effects among older adults and in low-density areas, indicating heatwaves can acutely raise demand for mental-health services and underscoring the need for targeted preparedness during severe heat events.