Effects of a laughter program on body weight and mental health among Japanese people with metabolic syndrome risk factors: a randomized controlled trial

BACKGROUND: While there have been several intervention studies on the psychological effects of laughter, few have examined both the psychological and physical effects. This study investigates the effects of a laughter program on body weight, body mass index (BMI), subjective stress, depression, and health-related quality of life (HRQOL) among Japanese community-dwelling individuals using a randomized controlled trial with a waitlist. METHODS: Overall, 235 participants (37 men and 198 women) aged 43–79 years (mean 66.9, median 67.0) were randomized into laughter intervention and control groups (n = 117 and n = 118, respectively) to participate in a 12-week laughter program. Body weight, subjective stress, subjective well-being, and HRQOL were measured at the baseline, with a 12-week follow-up. The laughter program intervention’s effects on these factors were analyzed using an analysis of covariance adjusted by age, sex, risk factors, medication, and area. Furthermore, Pearson’s correlation and a general linear model analyzed the relationship between participants’ BMI and psychological index changes. RESULTS: The comprehensive laughter program significantly improved the mean body weight (p = 0.008), BMI (p = 0.006), subjective stress (p = 0.004), subjective well-being (p = 0.002), optimism (p = 0.03), and physical component summary (PCS) scores of HRQOL (p = 0.04). A similar tendency occurred for the mean changes in BMI and subjective stress score by area, sex, and age. Moreover, there was a significant and negative correlation between the change in BMI and PCS change (p = 0.04). CONCLUSION: The comprehensive 12-week laughter intervention program, mainly comprising laughter yoga, significantly improved physical and psychological functions such as body weight, BMI, subjective stress, subjective well-being, and HRQOL among predominantly elderly Japanese community-dwelling individuals with metabolic syndrome risk factors. Moreover, PCS improved among participants who reduced BMI after the intervention. These results suggest that the laughter program may help reduce body weight in participants with metabolic syndrome risk factors by reducing stress and improving HRQOL and mental health factors, such as subjective well-being and optimism. TRIAL REGISTRATION: Registered with the University Hospital Medical Information Network Clinical Trials Registry UMIN-CTR000027145 on 27/04/2017. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-022-03038-y.