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Hot nights linked to more OHCA

Association between nighttime heat exposure and emergency hospitalization for out-of-hospital cardiac arrest: A time-stratified case-crossover study in Japan
International Journal of Biometeorology · 2026-10-23 · Added 25 October 2026

A nationwide time-stratified case-crossover study of 135,898 emergency hospitalisations for OHCA in Japan found hot nights (minimum temperature above the regional 92.5th percentile) were associated with a 9% higher OHCA hospitalisation risk, with the highest risks in people aged 75+ and women in northern regions.

Study type

Case-control

Design

Time-stratified case-crossover, nationwide administrative database (2011–2021)

Participants

135,898 emergency hospitalisations for OHCA in Japan

Main finding

Hot nights were associated with more OHCA hospitalisations (RR 1.090, 95% CI 1.047–1.135); RRs were higher in people ≥75 (1.295) and women in northern regions (1.352), and higher again for both groups where air conditioners were less common

Caveat

Hospitalisation-based — arrests not transported or dead at scene are invisible, and daily minimum temperature is a crude exposure measure

Bottom line

Hypothesis-generating

Learning goal

Recognise hotter nighttime temperatures as a driver of out-of-hospital cardiac arrest risk in older and female patients.

More

• Topic: Cardiac arrest
• Daily scan: 25 October 2026
• Podcast: Paramedic Papers Daily, 25 October 2026

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