Physical activity, such as a brisk walk, reduces mortality.
Here are some stats on lifespan and exercise:
Having a normal weight but being inactive: -3.1 years.
Having a normal weight and being active: +7.2 years.
Walking at least 150 minutes a week: +3.4-4.5 years.
Even low amounts of activity, such as 75 minutes of walking a week, adds 1.8 years.
Bottom line: maintaining a normal weight and being active adds the most years to your life, but even some activity is better than none.
Personal Trainer, Fitness Instructor since 1998.