Staying active is more important than ever for seniors. Adopting such painless habits as walking 30 minutes a day or parking farther from the supermarket can lower the risk of dementia and help relieve chronic pain. It can also be a great mood booster. A 2008 study of people in 80 countries found that after the onset of middle age (40 for U.S. women and 50 for men), people enter the highest-risk age group for depression. Gloom leads to lethargy, and lethargy exacerbates the sadness. Getting your blood pumping breaks that cycle.