Weather May Shape a Heart Risk for Runners

Researchers examined 12 years of Taipei Marathon data from Taiwan, covering more than 316,000 full- and half-marathon participants. They compared sudden cardiac arrests during each event with shifts in apparent temperature over the preceding week. Apparent temperature reflects how conditions feel to the body, including the effects of wind and humidity.

Greater day-to-day variation in apparent temperature was associated with more cardiac arrests. For every increase in temperature variability, the cardiac-arrest rate was more than six times higher. Even so, cardiac arrest remained extremely uncommon: only 13 cases occurred among the runners studied. Most happened in the last quarter of the race, after prolonged exertion, and the rate was higher among men than women.

The researchers proposed that repeated adjustments to changing temperatures might place additional strain on the body. Temperature shifts can influence heart rate and blood pressure as the heart, blood vessels and other systems work to maintain a stable body temperature. During a marathon, those systems are also supplying oxygen to working muscles. Because the study was observational, it found an association rather than proof that weather changes caused the events. With so few cases, larger studies are needed to confirm whether temperature variability is truly a cardiac risk factor.