Researchers have discovered that laughter may indeed be the best medicine after all. A new study published in PLOS One has found that spontaneous laughter can significantly reduce levels of the stress hormone cortisol, leading to positive effects for overall health.
When human bodies respond to stress, whether it’s physical (e.g. disease) or psychological (e.g. anticipating a threat), a system called the hypothalamic-pituitary-adrenal (HPA) axis is activated. The stress hormone, known as cortisol, is released as part of this.
Some studies suggest that spontaneous laughter can reduce levels of cortisol. Genuine laughter is intuitive, with brain pathways specific to laughter even developing before brain pathways for speech. Laughter and humor has been found to be beneficial for health, such as by increasing pain tolerance and improving general well-being in various medical settings.
Although many studies have proposed that laughter can decrease cortisol levels, these studies often had recruited only a small number of individuals, creating a difficulty in drawing definitive conclusions.
To clarify this further, researchers Caroline Kaercher Kramer (based at the University of Toronto, Canada) and Cristiane Bauermann Leitao (based at the Hospital de Clínicas de Porto Alegre, Brazil) conducted a systematic review and meta-analysis of studies.
This process involved pooling together relevant literature and scrutinizing them as a whole, in order to robustly evaluate the impact of spontaneous laughter on the stress response, as measured by cortisol levels.
Kramer and Leitao focused on randomized controlled trials (where participants are randomly assigned to either the experimental group or the control group) and quasi-experiments (a true experiment but without random assignment).
Four randomized controlled trials and four quasi-experiments were selected, published from 1989 to 2021, containing data from a total of 315 participants who were on average around 39 years old.
Laughter was induced by participants in the experimental group watching a comedy movie (five studies), undergoing laughter therapy conducted by a trained laughter therapist (two studies), or undergoing a self-administered laughter therapy (one study). The control group completed non-humorous usual activities.
Cortisol levels were measured through blood or saliva samples, and the change in cortisol levels before and after laughter was compared across the experimental group and the control group.
This is what the researchers found. Analysis of the data revealed an overall significant reduction in cortisol levels (31.9%) which was induced by laughter, compared to the control group.
Upon further investigation, the authors discovered that even a single laughter session (lasting 9 to 60 minutes) induced a significant reduction in cortisol levels (36.7%), as compared to the control group.
Interestingly, there was no impact of the duration of laughter on cortisol levels.
“The impact on [the] HPA axis found in our analyses suggests that genuine laughter holds positive effects for overall health as the excessive/prolonged cortisol secretion associated with chronic HPA-axis stimulation has negative implications for both physical and psychological diseases including obesity, depression, and chronic pain,” concluded Kramer and Leitao.
The authors reinforced how their results supported other research demonstrating the benefits of laughter and reduced cortisol.
Laughter has been found to have a cardioprotective effect (in other words, it protects the heart) by reducing the chances of developing coronary heart disease. The results also support literature which has highlighted potentially positive metabolic effects of reduced cortisol levels, for instance the increased stimulation of hair follicles, which ultimately leads to hair growth.
A few limitations are to be noted, one of which is that there are differences in the methods of inducing laughter between the studies. The time that cortisol levels were measured in participants varied between the studies, and may also have influenced the results.
The study, “Laughter as medicine: A systematic review and meta-analysis of interventional studies evaluating the impact of spontaneous laughter on cortisol levels”, was authored by Caroline Kaercher Kramer and Cristiane Bauermann Leitao.