Can running 2 hours a week, generate an increase in life expectancy of 3.2 years, for a net gain of about 2.8 years.? This study suggests so.
"Cumulatively, the data indicated that running, whatever someone’s pace or mileage, dropped a person’s risk of premature death by almost 40 percent, a benefit that held true even when the researchers controlled for smoking, drinking and a history of health problems such as hypertension or obesity.
Using those numbers, the scientists then determined that if every non-runner who had been part of the reviewed studies took up the sport, there would have been 16 percent fewer deaths over all, and 25 percent fewer fatal heart attacks. (One caveat: the participants in those studies were mostly white and middle class.)