Blisters and shin splints may not be the only health hazards of marathons—new research shows ambulances forced to navigate around road closures took longer to get to the hospital during U.S. marathons, and that some elderly patients hospitalized on marathon days had a higher risk of dying.

The research, published in the New England Journal of Medicine, found ambulances took 4.4 minutes longer, on average, to get elderly patients to the hospital before noon on marathon day during the 11 largest U.S. marathons, compared with...