Overview
- The Nature Health study, published in July 2026, analyzed more than 2.6 million warm-season hospital admissions from 852 sites across Brazil, Canada, Chile and New Zealand and found multi-day heatwaves raise emergency and inpatient visits for behavioral and mental-health disorders.
- Researchers defined heatwaves as at least four consecutive days above a location’s 97.5th percentile of daily mean temperature and tied prolonged hot spells to acute worsening of mood disorders, anxiety, psychosis, substance use and self-harm.
- Experts say the harms likely work through clear mechanisms: hot nights that disrupt sleep, direct physiological stress, and higher sensitivity to medications that impair the body's ability to cool.
- The study highlights who is most at risk—older adults, people in low-density communities and young people showing steep rises in admissions in some analyses—and recommends targeted actions such as neighborhood cooling, welfare checks and heat-aware clinical care.
- The findings build on earlier peer-reviewed work and warn that as heatwaves grow more frequent and intense health systems should expect higher mental-health demand while policymakers expand cooling, access to care and heat-prepared public-health plans.