Laughter reduces stress hormones like cortisol and epinephrine, thus stimulating the immune system. In Alternative Therapies in Health & Medicine in March 2003, researchers showed that laughter increased natural killer (NK) cell function, as well as many other types of immune system cells.[1]
[1] Bennet, M., J. Zeller, and L. Rosenberg. “the effect of mirthful laughter on stress and natural killer cell function.” Alternative Therapies in Health & Medicine Vol. 9. (Issue 2, 2003): 38-43.
