Running too much could shorten your lifespan

Despite running regularly being linked to a host of health benefits, including weight control, stress reduction, better blood pressure and cholesterol, a new study suggests that running may not be all that beneficial.

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, CBS News reported.

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.

Dr. Martin Matsumura, co-director of the Cardiovascular Research Institute at the Lehigh Valley Health Network in Allentown, Pennsylvania said that the study didn't find any differences that could explain these longevity differences.

Matsumura presented the findings Sunday at the American College of Cardiology's annual meeting in Washington, DC.

Even though the heart disease risk factors couldn't explain the shorter longevity of high-mileage runners, there do seem to be potentially life-shortening ill effects from that amount of running, Dr. James O'Keefe, director of preventive cardiology at the Mid-American Heart Institute in Kansas City said.

O'Keefe, who reviewed the findings, believes there may simply be "too much wear and tear" on the bodies of high-mileage runners.

Chronic extreme exercise, O'Keefe said, may induce a "remodeling" of the heart, and that could undermine some of the benefits that moderate activity provides.