Living longer is related to the number of calories burned per week. Dr. Ralph Paffenbarger conducted a highly acclaimed and comprehensive study for the US Public Health Service, started in the 1960s. Results have been published in the Journal of the American Medical Association, April 1995 (co-authored by Doctors Lee and Heieh).
The conclusion: as the amount of exercise increases, rates of death from all major causes are reduced. Those who exercise more can statistically predict that they will live longer than they would when sedentary or with minimal exertion. His extensive research has also shown that the more calories burned, the greater the benefit.
From Women's Complete Guide to Running, page 60-61.