The term midlife crisis has become a cliché. Nevertheless, middle age can be an emotional low point. A 2008 study of 2 million people in 80 countries found that the middle-age years were associated with the highest risk of depression: at about age 40 for American women and 50 for men. (The data suggest that mood improves from the 50s on.) One of the best ways to promote emotional well-being is to get your blood pumping even a simple daily walk outside will do. And if any of your bad habits, like smoking or heavy drinking, have persisted into middle age, now is the time to kick them. "Tobacco just no," says Samet. "There's no better way to kill yourself in middle age."