Marathons can be risky for hearts, but not necessarily those of the runners.
Residents who live near a marathon course - or location of other significant public event like parades, footy games, concerts and showgrounds - are less likely to survive a heart attack due to the extra time it needs to reach the hospital when an event is on, according to new research from the Harvard Medical School.
The concerns have been raised in the New England Journal of Medicine ahead of the Boston Marathon, which is due to get underway on Monday (local time).
The research, led by Dr Anupam Jena, found that for every group of 100 people suffering a heart attack or cardiac arrest, three to four more died within a month if they had sought emergency care on a marathon day versus another time.
Dr Jena said the publication timing of the research was a chance coincidence with Boston's 42 kilometre run but he hopes it will raise some attention to the issue.
The study included marathons in Boston, Chicago, Honolulu, Houston, Los Angeles, Minneapolis, New York City, Orlando, Philadelphia, Seattle and Washington between 2002 and 2012. It did not include 2013, when bombs at the Boston Marathon might have caused unusual delays.
Dr Jena came up with the idea for the study when he missed watching his wife run the marathon because of traffic jams.
"She made the offhand remark, 'Gee, I wonder what happens to people who need to get to the hospital during one of these large races,"' he said.
Researchers used patient medical records to determine if they were local residents, not race participants.
They found the death rate within 30 days was 28 per cent for those who suffered a heart attack on a marathon day, compared to 25 per cent for those who didn't.
The study also found average ambulance times were more than four minutes longer on race days.
