"Trying to maintain weight and fitness doesn't mean you have to be an Olympic athlete," says Samet. But a daily routine of physical activity gets more and more important as you age — not only to prevent weight gain and chronic illness but also to keep the brain sharp. Studies have shown that even small amounts of moderate exercise can help reduce the risk of dementia. In addition to cardiovascular exercise and strength training, doctors advise working on balance and flexibility, which can help protect against falls and injury in later life.