Overview
- University of Tokyo researchers and the Tokyo Metropolitan Medical Examiner released an updated joint analysis on June 18–19, 2026 after studying 1,447 heatstroke deaths in Tokyo's 23 wards from 2013–2023.
- The study finds daytime maximum temperatures above 27.1°C are associated with a sudden rise in heatstroke death risk and establishes 31.0°C as the point where elevated danger persists for four to five days.
- Each 1°C increase on days over 31.0°C raises the five‑day mortality risk by about 1.5 times regardless of age or sex, with people aged 85 and older and women at particularly higher risk.
- Not having air conditioning greatly increases danger at very high temperatures, with mortality risk more than three times higher at 33°C and about seven times higher at 36°C compared with those with AC.
- Tokyo authorities are using the results to urge people to use air conditioning once daytime highs exceed 27.1°C and to seek medical care for lingering symptoms, while researchers say the findings underscore growing heat and cardiovascular risks as temperatures climb.