Actually, there is some modern science in Medicine (more applied than pure), so where is the scientific evidence for this claim?   Apparently when we laugh, we exercise our muscles, get blood flowing, decrease our blood pressure and stress hormones, improve sleep patterns and boost our immune system. It’s a new area of research known as ‘Psychoneuroimmunology’ – the study of how emotions affect our nervous and immune systems. It’s still a relatively new area of research, but the insights are promising.

Eight studies (315 participants; mean age 38.6) met our inclusion criteria; four were RCTs and four were quasi-experiment studies. Five studies evaluated the impact of watching a humour/comedy video, two studies evaluating laughter sessions administered by a trained laughter therapist, and one study evaluating a self-administered laughter program. Pooling these data showed a significant reduction in cortisol levels by 31.9% (95%CI -47.7% to -16.3%) induced by laughter intervention compared to control group with no evidence of publication bias (P = 0.66). Sensitivity analyses demonstrated that even a single laughter session induced a significant reduction of 36.7% in cortisol (95%CI -52.5% to -20.8%). In addition, analyses including the four RCTs reinforced these results by demonstrating a significant reduction in cortisol levels promoted by laughter as compared to the placebo arm [-37.2% (95%CI -56.3% to -18.1%)].