Death rates from heart attacks are nearly 4 percent higher during large marathons in major U.S. cities, possibly due to road closures delaying the arrival of patients to the hospital, according to a study published this week in the New England Journal of Medicine.

By the numbers — Researchers from Harvard Medical School analyzed 30-day death rates for Medicare beneficiaries admitted to hospitals for heart attacks on the days of the 11 largest U.S. marathons, comparing them to rates from nonrace days and from hospitals outside of the area affected by the marathon. They found that mortality rates for marathon-affected hospitals were 3.7 percentage points higher — 28.6 percent versus 24.9 percent — than in other hospitals or on nonrace days.

The analysis found that ambulance transport times increased from 13.7 minutes on nonrace days to 18.1 minutes on marathon days, without any difference in the number of miles driven. The higher death rates suggest that three to four additional people would die each year because of the 11 marathons considered in the study.

Bottom line — The study is looking at past data rather than controlling the parameters of the study, and so is not able to draw any firm conclusions about the relationship between marathons, road closure and heart attack deaths. But the researchers were able to rule out many other possible explanations, including that marathons brought more visitors or that race participants were incurring heart attacks. The study authors suggested that if ambulances were delayed it is likely that patients arriving by private transportation were delayed even longer.