If you want to live longer and better, break out those jogging shorts. A recent study determined that people who exercised had longer leukocyte telomeres — the parts of white blood cells that shorten with age and eventually lead to cell death. Exercise also showed an anti-inflammatory effect in 4,000 adults who participated in a 2006 study. One reason why exercise may stave off aging is because it naturally increases hormone levels. “As you age, your hormone levels drop, and that changes your body composition, your energy levels, and your quality of life,” says Vincent Giampapa, MD. “Exercise is the easiest, least expensive way to balance your hormones. Twenty minutes of aerobics followed by 40 minutes of weight training or yoga actually changes your testosterone level, your DHEA level, your cortisol level, your thyroid hormone level, as well as a number of other hormones.” But as you get older, you'll need to do it more and more to see benefits, he says. So if you're in your 30s, aim for exercise three times a week; in your forties, four times a week; and so on.