We found that during genuine laughter energy expenditure and HR increased by up to 20% above resting.
Laughter is a unique human behavior naturally occurring in a variety of social situations. Facial, respiratory and laryngeal muscles are all recruited for laughter production2
leading to changes in lung volume and dynamic compression of the airways.15
These disturbances of the chest walls and other parts of the body may cause physiological changes requiring increased oxygen consumption leading to a higher HR. Logic suggests that an increase in HR and oxygen consumption should cause an increase in EE. Indeed, participants in our study had 10–20% higher EE during episodes of laughter than during rest. This increase was dependent on laugh intensity as measured by its duration and rate. Although, to our knowledge, no studies measuring energy cost of laughter have been reported, Boone et al
in their pilot study with eight college students, have shown a significant increase in stroke volume and cardiac output during viewing a laughter evoking film clip.
To place our data in perspective, we compared these laughter outcomes with some routine daily activities. Sedentary activities such as light clerical work, writing or playing cards can also increase EE by approximately 10–20%. Other forms of more intense physical activity such as jogging, or household chores can increase EE by 100% or more.17
Energy deficit of 170 kJ/day could be obtained by walking approximately half to one kilometer. Therefore, although laughter cannot replace exercise or other forms of intense physical activity, its production should not be discounted in the total balance of energy and should be considered a component of the non-exercise activity thermogenesis.18
We have calculated that the energy cost of 15 min of laughter ranges from 40 to 170 kJ (10–40 kcal), depending on individual body weight and laughter intensity. This amount of energy expenditure during 1 year, with no changes in other components of energy balance, may translate into an annual weight loss of 0.5–2km of body weigh, if all other components of energy balance remained unchanged.
Heart rate during laughter episodes was significantly higher than during rest in our study. There are several reasonable explanations for this increase. Mild exercise inhibits the parasympathetic nervous activity resulting in higher HR.19
Moderate or strong exercise activates sympathetic activity with simultaneous withdrawal of parasympathetic nerve activity.20,21
It has been shown that laughter has strong but transient effects on the autonomic nervous system22
and may contribute to cardioprotection in some personality traits.10
In some studies, laughter affected hormonal response, mostly as an effect of increased level of circulating catecholamines.23
suggested that the association of some emotions with HR change might reflect association with a motor program or action tendency, which makes significant metabolic demands on the heart. Thus, we could assume that similar mechanisms contributed to the increased HR and EE in our participants during the laugh episodes.
Our data must be interpreted with some caution. First, our study was carried out in young adults, which limits the applicability of our results to other age groups. Second, we used a room calorimeter for EE measurements and dyads as measurements units to create a comfortable yet strictly controlled environment. Laughter is far more likely to occur in social situations than in isolation25
and is more likely to occur with friends than with strangers.10
To ensure adequate laugh production, participants were therefore asked to bring a friend and to participate in dyads. This arrangement most likely reduced anxiety about being in the testing environment. The limitation was that oxygen consumption and carbon dioxide production were measured for dyads rather than individuals. In normal healthy adults, however, interindividual differences in resting EE are relatively small.26
Small EE measurement errors are inherent but mostly systematic and should not affect the difference between EE at rest and laughter EE measured in a strictly controlled environment. Furthermore, using an average increase in EE minimized bias caused by the differences in body mass between individuals in a single dyad. Differences in body composition between individuals in dyads did not affect laughter EE (paired t
To ensure that laughter was genuine, participants were unaware that the focus of the study was laughter. They produced various amount of laughter as measured by its duration and rate; both inter- and intra-individual variability was high. Differences between the quartiles sorted by laughter duration shown in illustrate this variability well. A plausible explanation for such variability is that humor appreciation and any resulting laughter depend not only on cognition but other factors such as education, language, semantic, and culture. The level of friendship and social comfort across dyads was unlikely to be equivalent and therefore lead to variability in the laughter duration and rate. It is likely that different social environments (i.e., a comedy show) could facilitate more frequent, longer and more intense laughter episodes and consequently would be more energetically expensive.
Figure 4 Laughter energy expenditure (EE) calculated as a difference between EE at rest and during viewing humorous film clips intended to evoke laughter (Laughter EE (kcal/min)=EE during laugh − EE at rest) and laughter heart rate (laughter HR) calculated (more ...)
In conclusion, genuine voiced laughter causes a 10–20% increase in energy expenditure and HR above resting values. We calculated that 10–15 min of laughter could increase energy expenditure by 50–170 kJ (10–40 kcal) per day.