Marathons can prove just as fatal for non-runners on the big day –

Any event that draws a crowd and causes traffic detours – parades, sports fixtures, concerts – may cause similar problems, researchers warn.

It’s more than inconvenience: for every 100 people suffering a heart attack or cardiac arrest, three to four more died within a month if they had sought care on a marathon day versus another time, the study found.

It was published by the ‘New England Journal of Medicine’, just before Boston’s annual marathon race, set for Monday.

The publication timing was by chance, but “hopefully it will raise some attention around the issue”, said the study leader Dr Anupam Jena of Harvard Medical School.

The study included marathons in Boston, Chicago, Houston, Los Angeles, New York City, Orlando, Philadelphia, Seattle and Washington between 2002 and 2012.

Researchers compared death rates for patients hospitalised on the day of the race versus five weeks before or after it, or in surrounding areas less affected by closed roads.

The rate of death within 30 days was 28pc for those stricken on a marathon day versus 25pc for the others. Average ambulance times were more than four minutes longer on race days.

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