Lead author Peter Kokkinos of the Veterans Affairs Medical Center in Washington said the Veterans Affairs study is the largest known study to assess the link between fitness and mortality.

"It is important to emphasize that it takes relatively moderate levels of physical activity -- like brisk walking -- to attain the associated health benefits," Kokkinos said in a statement.

"Certainly, one does not need to be a marathon runner. This is the message that we need to convey to the public."

Kokkinos and colleagues investigated exercise capacity as an independent predictor of overall mortality in 6,749 African-American men and 8,911 Caucasian men, who were tested by treadmill test and were tracked for an average of 7.5 years.

The study, published in the Circulation: Journal of the American Heart Association, found men who achieved "very highly fit" levels had a 70 percent lower risk of death compared to those in the "low fit" category.

"Our findings show that the risk of death is cut in half with an exercise capacity that can easily be achieved by a brisk walk of about 30 minutes per session five to six days per week," Kokkinos added.