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AI-DRAFTED — PHYSICIAN REVIEW IN PROGRESSThe citation for this entry was checked against Crossref and PubMed, but its summary and interpretation were drafted by an AI model from the published abstract and have not yet been individually read by a physician. Read the linked source before relying on this operationally.
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Meteorological and Environmental Factors Associated With Sudden Cardiac Arrest During Marathons in Japan[1]

Kato J, Manabe T, Iwagami M, Yamasawa F, Honda Y · 2026 · JACC Adv

Summary

Nationwide race-level study of JAAF-certified full marathons in Japan (April 2011-March 2020), linking 4.53 million runners and 75 identified SCA cases to race-start meteorology (temperature, humidity, solar radiation, wind, precipitation, pressure) and ambient air pollutants (PM2.5, SPM, photochemical oxidants, SO2, NO2, CO) via Poisson regression adjusted for race and participant composition. The signal was temperature: LOWER ambient temperature at race start was associated with HIGHER SCA risk (adjusted incidence rate ratio 0.94 per 1 C increase; 95% CI 0.90-0.99). No air pollutant showed a statistically significant association. The authors note these races are held predominantly in autumn and winter.

So what

A large, adjusted dataset putting a number on the cold-as-cardiac-risk mechanism the Purple Guide Weather chapter asserts and the weather-beyond-heat page (#20) argues: for marathon runners, each 1 C DROP in start temperature raised SCA risk (~6% per degree), while air pollution did not reach significance. It reframes the reflexive event-medicine fixation on heat - for the exerting cardiac at a cold-weather endurance race, the environmental risk runs the other way. Directly reinforces the weather page's "cold has a cardiac tail" claim and the library's Goldberg cold-transport finding, and tells a cold-race medical director to expect cardiac, not just hypothermic, load. Race-level ecological design (not individual-level), so cite for the association and direction, not causation.

Key findings

  • Japan, JAAF full marathons 2011-2020, 4.53M runners, 75 SCA
  • Lower race-start temperature -> higher SCA risk: adjusted IRR 0.94 per 1C increase (95% CI 0.90-0.99)
  • No significant association for any ambient air pollutant (PM2.5, NO2, SO2, CO, etc.)
  • Races predominantly autumn/winter — the cold-exertion window
  • Quantifies cold-as-cardiac-risk; reinforces weather page #20 and Goldberg cold-transport; free PMC

Read the paper