Laughter up-regulates the genes related to NK cell activity in diabetes

Humor and Quality of Life in Adults With Chronic Diseases: A Systematic Review

Individuals grappling with chronic ailments often undergo a deterioration in their overall quality of life (QoL), encompassing psychological, social, and physical dimensions of well-being. Acknowledging that humor has demonstrated the potential to engender favorable effects on QoL, this systematic review endeavors to investigate the correlation between humor and QoL among adults contending with chronic health conditions. A comprehensive review of quantitative data was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. PubMed/MEDLINE, PsycINFO, and Cumulative Index to Nursing & Allied Health (CINAHL) were comprehensively searched from the establishment of each database up to June 22, 2023. Furthermore, reference lists of the included datasets and pertinent review articles were scrutinized exhaustively. The Newcastle-Ottawa Scale (NOS) was employed to assess the quality of eligible studies. A total of 18 studies satisfied the inclusion criteria. These studies encompassed a diverse spectrum of chronic disease categories (including cardiovascular diseases, various types of cancer, etc.) and collectively involved a participant cohort comprising 4,325 individuals. Remarkable findings surfaced, indicating a noteworthy association between distinct facets of humor-such as one's sense of humor, coping humor, humor styles, and laughter-and psychological QoL. Nonetheless, the relationship between humor and physical QoL exhibited a more intricate pattern, characterized by mixed outcomes. Despite the limited and inconsistent evidence across studies, humor appears to exhibit a positive association with QoL.

Subjective Happiness, Frequency of Laughter, and Hypertension: A Cross-Sectional Study Based on the Japan Gerontological Evaluation Study (JAGES)

In recent years, positive psychological factors, such as subjective happiness and laughter, have been reported to be associated with cardiovascular disease. In this study, we examined the relationship of hypertension with subjective happiness and frequency of laughter using the data from the Japan Gerontological Evaluation Study (JAGES). Of the 138,294 respondents, 26,368 responded to a version of the self-administered questionnaire that included a question about the frequency of laughter in the JAGES 2013. In total, 22,503 (10,571 men and 11,932 women) were included in the analysis after excluding those with missing responses regarding a history of hypertension, frequency of laughter, and subjective happiness. The prevalence of hypertension in this study was 10,364 (46.1%). Multivariate logistic regression analysis showed that age, female sex, obesity, infrequent chewing, former and current drinker, seeing three to five friends, and the absence of hobbies were positively associated with hypertension. However, infrequent laughter/high level of subjective happiness, frequent laughter/high level of subjective happiness, being underweight, and current smoker were negatively associated with hypertension. As per the findings of this study, it was determined that subjective happiness was negatively associated with hypertension. Therefore, this study suggests that having more opportunities to feel happiness may be important in preventing hypertension.

The Effects of Laughter Yoga on Perceived Stress, Positive Psychological Capital, and Exercise Capacity in Lung Cancer Chemotherapy Patients: A Pilot Randomized Trial

BACKGROUND

Lung cancer is the malignant tumor with the highest morbidity and mortality rate in China. Although chemotherapy is effective in improving clinical symptoms, it causes a variety of acute and chronic side effects, seriously aggravating the psychological stress of patients. Laughter Yoga as a new type of aerobic exercise can effectively reduce stress levels and increase positive mood in patients. This study aimed to examine the effects of laughter yoga on perceived stress, positive psychological capital, and exercise capacity in lung cancer patients.

METHODS

This study was a randomized, single-blind, parallel-group trial. The study enrolled 84 lung cancer chemotherapy patients from a general hospital in central China. These patients were randomly allocated to control and intervention groups (n = 42 per group) after baseline assessments. Patients in the control group received routine care and those in the intervention group received laughter yoga intervention. Perceived stress, positive psychological capital, and exercise capacity were assessed at baseline, immediately post-intervention.

RESULTS

During the implementation of the study, there were 2 dropouts in each of the intervention and control groups. Ultimately, 80 patients in the control and intervention groups completed the trial. Patients who received laughter yoga intervention had significantly higher scores in positive psychological capital (P < .01, Cohen's d = 0.692) and exercise capacity (P < .01, Cohen's d = 0.659). Discernible differences were also observed in perceived stress (P < .01, Cohen's d = 1.087) between the 2 groups.

CONCLUSIONS

The results of this study suggest that laughter yoga is an effective way and may produce beneficial effects on perceived stress, positive psychological capital and exercise capacity.

Laughter yoga as an enjoyable therapeutic approach for glycemic control in individuals with type 2 diabetes: A randomized controlled trial

BACKGROUND

Laughter has been reported to have various health benefits. However, data on the long-term effects of laughter interventions on diabetes are limited. This study aimed to investigate whether laughter yoga can improve glycemic control among individuals with type 2 diabetes.

METHODS

In a single-center, randomized controlled trial, 42 participants with type 2 diabetes were randomly assigned to either the intervention or the control group. The intervention consisted of a 12-week laughter yoga program. Hemoglobin A1c (HbA1c), body weight, waist circumference, psychological factors, and sleep duration were evaluated at baseline and week 12.

RESULTS

Intention-to-treat analysis showed that participants in the laughter yoga group experienced significant improvements in HbA1c levels (between-group difference: -0.31%; 95% CI -0.54, -0.09) and positive affect scores (between-group difference: 0.62 points; 95% CI 0.003, 1.23). Sleep duration tended to increase in the laughter yoga group with a between-group difference of 0.4 hours (95% CI -0.05, 0.86; P = 0.080). The mean attendance rate for laughter yoga program was high (92.9%).

CONCLUSIONS

A 12-week laughter yoga program is feasible for individuals with type 2 diabetes and improves glycemic control. These findings suggest that having fun could be a self-care intervention. Further studies with larger numbers of participants are warranted to better evaluate the effects of laughter yoga.

CLINICAL TRIAL REGISTRATION

http://www.chinadrugtrials.org.cn, identifier UMIN000047164.

The Association between Laughter and Functional Dyspepsia in a Young Japanese Population

The potential health benefits of laughter are recognized in relation to several chronic diseases. However, no study has yet investigated the association between laughter and functional dyspepsia (FD). The purpose of this study was to investigate this issue in a young Japanese population.

METHODS

This study was conducted on 8923 Japanese university students. Information on the frequency of laughter and types of laughter-inducing situations, digestive symptoms (Rome III criteria) were obtained through a self-administered, web-based questionnaire.

RESULTS

The percentage of respondents who laughed out loud almost every day was 64.3%. On the other hand, 1.8% of the subjects reported that they rarely laughed. No association was found between the total frequency of laughter and FD. Laughing while talking with family and friends almost every day was significantly inversely associated with FD (adjusted odds ratio (OR): 0.47 (95% confidence interval (CI): 0.28-0.81); p for trend was 0.003). On the other hand, laughing while watching TV or videos and laughing while looking at comics or magazines independently showed a positive correlation with FD (TV or videos: adjusted OR, 1-5 times a week: 1.74 (95% CI: 1.16-2.60); comics or magazines: adjusted OR, 1-5 times a week: 1.78 (95% CI: 1.08-2.81)).

CONCLUSION

In this young Japanese population, no association between laughter frequency and FD was observed although laughing while talking with friends and family was independently and inversely associated with FD.

Occasions for laughter and dementia risk: Findings from a six-year cohort study

AIM

Currently, there is little evidence on the relationship between laughter and the risk of dementia, and since laughter is mainly a social behavior, we aimed to examine the association between various occasions for laughter and the risk of dementia in Japanese older adults.

METHODS

We draw upon 6-year follow-up data from the Japan Gerontological Evaluation Study, including 12 165 independent older adults aged 65 years or over. Occasions for laughter were assessed using a questionnaire, while dementia was diagnosed using the standardized dementia scale of the long-term care insurance system in Japan. Cox proportional hazards models were estimated, yielding hazard ratios and 95% confidence intervals (CIs).

RESULTS

The multivariable hazard ratio of dementia incidence for all participants in the groups for high versus low variety of occasions for laughter was 0.84 (95% CI: 0.72-0.98, P for trend <0.001). A greater variety of occasions for laughter was associated with a lower risk of dementia 0.78 (95% CI: 0.63-0.96, P for trend <0.001) among women, but was less pronounced for men, with significant associations only for the medium group. Laughing during conversations with friends, communicating with children or grandchildren, and listening to the radio were primarily associated with decreased risk.

CONCLUSION

A greater variety of laughter occasions in individual and social settings was associated with a reduced risk of dementia. Geriatr Gerontol Int 2022; 22: 392-398.

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.

Diabetes and Humor: A Preliminary Investigation

Diabetes can take a tremendous toll on physical and psychological health. Given the growing evidence of the benefits of humor, this study examined the association between diabetes and humor. The sample consisted of 249 participants: 72.3% with type 1 diabetes, 70.3% female, 89.5% Caucasian, and 70.9% college educated. Participants completed the Humor Styles Questionnaire (HSQ) and were compared with HSQ norms. On the affiliative humor scale, the diabetes group did not differ from the norm (P >0.05), nor did those with type 1 diabetes (P >0.05). Scores of those with type 2 diabetes were lower than the norm (P <0.05). On the self-enhancing humor scale, the diabetes group did not differ from the norm (P >0.05), nor did the subgroups with type 1 diabetes (P >0.05) or type 2 diabetes (P >0.05). The diabetes group was lower than the norm on aggressive humor (P <0.01), as were the subgroups with type 1 diabetes (P <0.01) and type 2 diabetes (P <0.05). The diabetes group was higher than the norm on self-defeating humor (P <0.01), as were the subgroups with type 1 diabetes (P <0.01) and type 2 diabetes (P <0.01). Results suggest that people with either type of diabetes are more inclined toward self-enhancing humor, are less inclined toward aggressive humor, and score higher on self-defeating humor, and those with type 1 diabetes are also inclined toward affiliative humor. Results are discussed relative to the sample being comprised of individuals with good glycemic control (mean A1C 7.06 ± 1.39%). This study offers a preliminary comparison of humor among people with diabetes versus those in a healthy norm group without diabetes.

Longitudinal Trends in Blood Pressure Associated With the Frequency of Laughter: The Circulatory Risk in Communities Study (CIRCS), a Longitudinal Study of the Japanese General Population

Background

The frequency of laughter has been associated with cardiovascular disease and related biomarkers, but no previous studies have examined association between laughter and changes in blood pressure levels. We sought to identify temporal relationships between frequency of laughter in daily life and systolic and diastolic blood pressure changes in participants from 2010 through 2014.

Methods

Participants were 554 men and 887 women aged 40–74 years who answered self-administered questionnaire quantifying frequency of laughter at baseline. We measured participant blood pressure levels twice using automated sphygmomanometers for each year from 2010 to 2014. The associations between laughter and changes in blood pressure over time were analyzed using linear mixed-effect models.

Results

There was no significant difference in blood pressure according to frequency of laughter at baseline in either sex. Men with frequency of laughter 1 to 3 per month or almost never had significantly increased systolic and diastolic blood pressure levels over the 4-year period (time-dependent difference: 0.96 mm Hg (95% confidence interval [CI], −0.2 to 1.8; P = 0.05). Changes in blood pressure associated with infrequent laughter (ie, 1 to 3 per month or almost never) were evident in men without antihypertensive medication use over 4 years (0.94 mm Hg; 95% CI, −0.2 to 2.0; P = 0.09) and men who were current drinkers at baseline (1.29 mm Hg; 95% CI, −0.1 to 2.3; P = 0.04). No significant difference was found between frequency of laughter and systolic (0.23 mm Hg; 95% CI, −1.0 to 1.5; P = 0.72) and diastolic (−0.07 mm Hg; 95% CI, −0.8 to 0.7; P = 0.86) blood pressure changes in women.

Conclusions

Infrequent laughter was associated with long-term blood pressure increment among middle-aged men.

Beneficial effect of laughter therapy on physiological and psychological function in elders

AIM

In the present study we investigated the effect of laughter therapy on physiological and psychological function in older people.

DESIGN

An open-label trial.

METHODS

Seventeen older people who regularly attended an elderly day care centre were recruited. Stand-up comedy as laughter therapy was performed once a week for 4 weeks. Parameters of physiological and psychological function were evaluated before and after laughter therapy.

RESULTS

Laughter therapy intervention resulted in a significant reduction in systolic blood pressure and heart rate, accompanied by a significant increase in plasma concentration of serotonin and a significant decrease in salivary concentration of chromogranin A. Questionnaire surveys of SF-8, GDS-15, and Vitality Index demonstrated alleviation of depression and improvement of sociability and activity in older people. Laughter therapy could be expected to become a practical treatment to improve quality of life of older people in an elderly day care centre.

Oxidative Stress and Inflammation Induced by Environmental and Psychological Stressors: A Biomarker Perspective

SIGNIFICANCE

The environment can elicit biological responses such as oxidative stress (OS) and inflammation as a consequence of chemical, physical, or psychological changes. As population studies are essential for establishing these environment-organism interactions, biomarkers of OS or inflammation are critical in formulating mechanistic hypotheses. Recent Advances: By using examples of stress induced by various mechanisms, we focus on the biomarkers that have been used to assess OS and inflammation in these conditions. We discuss the difference between biomarkers that are the result of a chemical reaction (such as lipid peroxides or oxidized proteins that are a result of the reaction of molecules with reactive oxygen species) and those that represent the biological response to stress, such as the transcription factor NRF2 or inflammation and inflammatory cytokines.

CRITICAL ISSUES

The high-throughput and holistic approaches to biomarker discovery used extensively in large-scale molecular epidemiological exposome are also discussed in the context of human exposure to environmental stressors.

FUTURE DIRECTIONS

We propose to consider the role of biomarkers as signs and to distinguish between signs that are just indicators of biological processes and proxies that one can interact with and modify the disease process. Antioxid. Redox Signal. 28, 852-872.

Homeostatic effect of laughter on diabetic cardiovascular complications: The myth turned to fact

AIMS

Laughter has been used for centuries to alleviate pain in morbid conditions. It was not until 1976 that scientists thought about laughter as a form of therapy that can modulate hormonal and immunological parameters that affect the outcome of many serious diseases. Moreover, laughter therapy was shown to be beneficial in type 2 diabetes mellitus (T2DM) by delaying the onset of many diabetic complications. Laughter is also described to influence the cardiovascular and endothelial functions and thus may protect against diabetic cardiovascular complications. In this review, we outline the different biochemical, physiological and immunological mechanisms by which laughter may influence the overall state of wellbeing and enhance disease prognosis. We also focus on the biological link between laughter therapy and diabetic cardiovascular complications as well as the underlying mechanisms involved in T2DM.

METHODS

Reviewing all the essential databases for "laughter" and "type 2 diabetes mellitus".

RESULTS

Although laughter therapy is still poorly investigated, recent studies show that laughter may retard the onset of diabetic complications, enhance cardiovascular functions and rectify homeostatic abnormalities associated with T2DM.

CONCLUSIONS

Laughter therapy is effective in delaying diabetic complications and should be used as an adjuvant therapy.

Affective immunology: where emotions and the immune response converge

Affect and emotion are defined as “an essential part of the process of an organism's interaction with stimuli.” Similar to affect, the immune response is the “tool” the body uses to interact with the external environment. Thanks to the emotional and immunological response, we learn to distinguish between what we like and what we do not like, to counteract a broad range of challenges, and to adjust to the environment we are living in. Recent compelling evidence has shown that the emotional and immunological systems share more than a similarity of functions. This review article will discuss the crosstalk between these two systems and the need for a new scientific area of research called affective immunology. Research in this field will allow a better understanding and appreciation of the immunological basis of mental disorders and the emotional side of immune diseases.

Effects of a Humor Therapy Program on Stress Levels in Pediatric Inpatients

OBJECTIVE

Disease and hospitalization generate stress, which can affect the response to treatment. Humor has been used in many hospitals to decrease stress. The aim of this study was to evaluate the impact of a humor therapy program on stress levels in pediatric inpatients.

METHODS

In the first phase, an intervention and a control group were studied over 2 consecutive 3-month periods; the interventions were performed by a team of artists trained in humor therapy. Salivary cortisol levels were measured by enzyme-linked immunosorbent assay, and the Weisz test, a pictorial chart that determines subjective stress perception, and the Parker test, which assesses objective stress, were applied. In the second phase, salivary cortisol levels were measured and the Weisz test was administered before and after the interventions.

RESULTS

A total of 306 patients were recruited into this study: 198 in the first phase (94 in the intervention group and 104 in the nonintervention group) and 108 in the second phase. There were no differences between groups regarding age, sex, or medical diagnosis. The children in the intervention group presented lower cortisol levels, lower scores on the Parker test, and higher scores on the Weisz test than children in the nonintervention group. In the second phase, the children showed lower salivary cortisol levels and higher scores on the Weisz test after the intervention.

CONCLUSIONS

Humor therapy has beneficial effects on stress and cortisol levels in pediatric inpatients. This supports the implementation and reinforcement of these therapies in pediatric hospitals.

Laughter is the Best Medicine? A Cross-Sectional Study of Cardiovascular Disease Among Older Japanese Adults

Background

We sought to evaluate the associations between frequency of daily laughter with heart disease and stroke among community-dwelling older Japanese women and men.

Methods

We analyzed cross-sectional data in 20 934 individuals (10 206 men and 10 728 women) aged 65 years or older, who participated in the Japan Gerontological Evaluation Study in 2013. In the mail-in survey, participants provided information on daily frequency of laughter, as well as body mass index, demographic and lifestyle factors, and diagnoses of cardiovascular disease, hyperlipidemia, hypertension, and depression.

Results

Even after adjustment for hyperlipidemia, hypertension, depression, body mass index, and other risk factors, the prevalence of heart diseases among those who never or almost never laughed was 1.21 (95% CI, −1.03–1.41) times higher than those who reported laughing every day. The adjusted prevalence ratio for stroke was 1.60 (95% CI, 1.24–2.06).

Conclusions

Daily frequency of laughter is associated with lower prevalence of cardiovascular diseases. The association could not be explained by confounding factors, such as depressive symptoms.

Effects of Laughter Therapy on Immune Responses in Postpartum Women

OBJECTIVE

To examine the effects of laughter therapy on secretory IgA (sIgA) in postpartum women.

METHODS

The study used a nonequivalent control group with nonsynchronized design. The participants were 76 postpartum women who agreed to participate in this study and were selected by convenience sampling (experimental group, n = 38; control group, n = 38). The data were collected from December 15, 2009, to April 8, 2010. The experimental group participated in a postpartum laughter program from a laughter therapy expert for 60 minutes per session, twice a week for 2 weeks, for a total of four sessions. To evaluate the effects of the postpartum laughter program, sIgA levels in breast milk were measured. The data were analyzed using SPSS WIN 20.0 software.

RESULTS

Immune response (sIgA) significantly differed between the experimental and control groups.

CONCLUSION

A postpartum laughter program can be applied as a complementary and alternative intervention to postpartum women in a transitional mother-infant care center.

'As above, so below' examining the interplay between emotion and the immune system

While the concept of a palpable relationship between our mental and physical well-being is certainly not new, it is only in the light of modern scientific research that we have begun to realize how deeply connected our emotional and immune states may be. We begin this review with a series of studies demonstrating how four fundamental emotional responses: anger, anxiety, mirth and relaxation are able modulate cytokine production and cellular responses to a variety of immune stimuli. These modulations are shown to be either detrimental or beneficial to a patient's health dependent on the context and duration of the emotion. We also discuss the reverse, highlighting research demonstrating how the loss of key immune cells such as T lymphocytes in clinical and animal studies can negatively impact both emotional well-being and cognition. Additionally, to give a more complete picture of the manifold pathways that link emotion and the immune system, we give a brief overview of the influence the digestive system has upon mental and immunological health. Finally, throughout this review we attempt to highlight the therapeutic potential of this burgeoning field of research in both the diagnosis and treatment of immune and disorders. As well as identifying some of the key obstacles the field must address in order to put this potential into practice.

“Does happiness help healing?” Immune response of hospitalized children may change during visits of the Smiling Hospital Foundation’s Artists

Psychoneuroimmunologic studies on positive emotions are few, and their clinical relevance is limited. Aims: This “SHoRT” (Smiling Hospital Research Team) study evaluates the effects that Smiling Hospital artists have on hospitalized children. Methods: Blood samples were taken in a non-painful way through branules in an accredited Infectology Ward, 30 minutes before and 1 hour after a visit of tale tellers, puppeteers and handicraft artists. 24 children were visited and 9 were included in the control group. Blood lymphocyte counts and Th1/Th2 cytokine levels were determined. Artists evaluated their effect on a subjective scale. Results: In the visited group, the increase of lymphocytes was 8.43% higher, the decrease was 12.45% lower, and the proportion of children showing increased lymphocyte counts was more increased. Changes were more marked after more successful visits. Authors found non-significant, still considerable changes in interferon-γ level (p < 0.055) and in Th1/Th2 cytokine ratios. Conclusions: This pediatric study suggests that immunological changes may develop when more attention is given to hospitalized children. Orv. Hetil., 2011, 152, 1739–1744.

Glucose metabolism disorders and the risk of cancer

Diabetes and cancer are diseases which take the size of an epidemic spread across the globe. Those diseases are influenced by many factors, both genetic and environmental. Precise knowledge of the complex relationships and interactions between these two conditions is of great importance for their prevention and treatment. Many epidemiological studies have shown that certain types of cancer, especially gastrointestinal cancers (pancreas, liver, colon) and also the urinary and reproductive system cancers in women are more common in patients with diabetes or related metabolic disorders. There are also studies showing the inverse relationship between diabetes and cancer, or the lack of it, but they are less numerous and relate mainly to prostate cancer or squamous cell carcinoma of the esophagus. Epidemiological studies, however, do not say anything about the mechanisms of these dependencies. For this purpose, molecular research is needed on the metabolism of cells (including tumor cells) and on metabolic dysfunctions that arise due to changes in the cell environment taking place in the sick, as well as in the intensely treated human organism.

Assessing the human immune system through blood transcriptomics

Blood is the pipeline of the immune system. Assessing changes in transcript abundance in blood on a genome-wide scale affords a comprehensive view of the status of the immune system in health and disease. This review summarizes the work that has used this approach to identify therapeutic targets and biomarker signatures in the field of autoimmunity and infectious disease. Recent technological and methodological advances that will carry the blood transcriptome research field forward are also discussed.

The effects of laughter on post-prandial glucose levels and gene expression in type 2 diabetic patients

This report mainly summarizes the results of our study in which the physiological effects of laughter--as a positive emotional expression--were analyzed with respect to gene expression changes to demonstrate the hypothesis that the mind and genes mutually influence each other. We observed that laughter suppressed 2-h postprandial blood glucose level increase in patients with type 2 diabetes and analyzed gene expression changes. Some genes showed specific changes in their expression. In addition, we revealed that laughter decreased the levels of prorenin in blood; prorenin is involved in the onset of diabetic complications. Further, laughter normalized the expression of the prorenin receptor gene on peripheral blood leukocytes, which had been reduced in diabetic patients; this demonstrated that the inhibitory effects of laughter on the onset/deterioration of diabetic complications at the gene-expression level. In a subsequent study, we demonstrated the effects of laughter by discriminating 14 genes, related to natural killer (NK) cell activity, to exhibit continuous increases in expression as a result of laughter. Our results supported NK cell-mediated improvement in glucose tolerance at the gene-expression level. In this report, we also review other previous studies on laughter.