Positive psychology—in a nutshell, the study of happiness—has found that the more joy you feel, the healthier you're likely to be. "Positive emotions make us feel lighter, happier and more at ease," says Dr. Rakel. It's hard to say, though, which comes first—if being happy improves health or if wellness makes it easier to feel joy. In 2008, the Mayo Clinic reported that "people in excellent health are almost twice as likely to be happier than those in merely good health."
Try it: Volunteering may increase your happiness and health, explains "mindfulneess" expert Saki Santorelli, Ed.D., associate professor of medicine at the University of Massachusetts Medical School. "There's a sense of giving back or helping out, and the mood is elevated. That happiness, inspiration or feeling of connectedness seems to improve health."