It makes sense to fool yourself. New research shows that feeling young actually makes your body age slower. A British study found that seniors who felt at least three years younger in age had a lower chance of dying over an eight year period than those who felt their age or older. The study also confirmed the power optimism—yes, you already know that. “Optimism in many ways is a self-fulfilling prophecy,” says one of the scientists. “If you feel your life and your health is largely under your control, and you believe you are capable of doing things like managing stress, eating right and exercising, then you are more likely to do those things.”