“You may have heard the advice ‘If you exercise, you'll live longer.’ The good news -- or the bad news, if you hate doing anything more active than downloading iTunes -- is that it's true. Research backs this up. A 2007 study in the Journal of the American Medical Assn. found that fitter people lived longer, even if they had extra pounds around the middle. Among 2,603 adults 60 and older enrolled in that longitudinal study, the fittest people (those who did best on a treadmill test) also had the lowest risk factors for hypertension, diabetes and high cholesterol. Most of the negative changes to our bodies over time can be chalked up to two things, says Wojtek Chodzko-Zajko, head of the department of kinesiology at the University of Illinois at Urbana-Champaign: normal aging and disease-related aging (that is, changes accelerated by illnesses and conditions such as diabetes and heart disease).