Run for Your Life(21-year period. The participants were 50...),Health

At 19 years, just 15 percent of the runners had died, compared with 34 percent of the non-runners.

Also, said Fries, who is almost 70, runs 20 miles a week and plays tennis, "Running delayed the onset of disability by an average of 16 years, and that is largely a conservative number, because the control group was pretty darn healthy."

And the slew of predicted orthopedic injuries never materialized.

Surprisingly, the health gap between runners and non-runners only increased with time. "I always thought that the two curves would start to parallel each other and that eventually aging would overpower exercise," Fries said. "I think that will happen, but we can't find even a little twitch toward that gap narrowing in the present time."

Which is not to say that running is the only activity that's good for you.

"Vigorous activity has a really dramatic impact, but we can't ignore that there are also helpful benefits to people who are active at all levels, meaning those people who are just out walking" said Ory. "It's so important to be physically active your whole life, not just in your 20s or 40s, but forever."

Added Dr. Suzanne Steinbaum, director of women and heart disease at Lenox Hill Hospital in New York City: "Exercise is like the most potent drug. Exercise is by far the best thing you can do."

More information

Visit the U.S. National Institute on Aging for more on healthy aging.

SOURCES: James Fries, M.D., emeritus professor of medicine, Stanford University School of Medicine, Stanford
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