Running regularly has long been linked to a host of health benefits, including weight control, stress reduction, better blood pressure and cholesterol.
However, recent research suggests there may a point of diminishing returns with running.
A number of studies have suggested that a "moderate" running regimen -- a total of two to three hours per week, according to one expert -- appears best for longevity, refuting the typical "more is better" mantra for physical activity.
The researchers behind the newest study on the issue say people who get either no exercise or high-mileage runners both tend to have shorter lifespans than moderate runners. But the reasons why remain unclear, they added.
The new study seems to rule out cardiac risk or the use of certain medications as factors.
"Our study didn't find any differences that could explain these longevity differences," said Dr. Martin Matsumura, co-director of the Cardiovascular Research Institute at the Lehigh Valley Health Network in Allentown, Pa.
Matsumura presented the findings Sunday at the American College of Cardiology's annual meeting in Washington, D.C. Studies presented at medical meetings are typically viewed as preliminary until published in a peer-reviewed journal.
Matsumura and his colleagues evaluated data from more than 3,800 men and women runners, average age 46. They were involved in the Masters Running Study, a web-based study of training and health information on runners aged 35 and above. Nearly 70 percent reported running more than 20 miles a week.
The runners supplied information on their use of common painkillers called NSAIDs (nonsteroidal anti-inflammatory medications such as ibuprofen and naproxen/Aleve), which have been linked with heart problems, as well as aspirin, known to be heart-protective. The runners also reported on known heart risk factors such as high blood pressure, high cholesterol, diabetes, family history of heart disease and smoking history.