Laughter

Dr. Lee Berk and fellow researcher Dr. Stanley Tan of Loma Linda University in California have been studying the effects of laughter on the immune system. To date their published studies have shown that laughing lowers blood pressure, reduces stress hormones, increases muscle flexion, and boosts immune function by raising levels of infection-fighting T-cells, disease-fighting proteins called Gamma-interferon and B-cells, which produce disease-destroying antibodies. Laughter also triggers the release of endorphins, the body's natural painkillers, and produces a general sense of well-being.

Source: Humor.com