According to the United Nations, there are currently around 962 million people aged 60 years and above in the world, comprising 13% of the global population. It is projected that the number of older people in the world will reach 1.4 billion by 2030, 2.1 billion by 2050, and rise to 3.1 billion by 2100, with a growing rate of about 3% per year [1]. Iran, with 9.3 percent older adults aged 60 years and over in 2016, like many other countries around the world, is heading towards declining fertility rates combined with improvements in life expectancy [2]. As the population ages, identifying novel ways to maintain and promote the well-being of older adults is imperative.

According to the gerontological and geriatric literature, one of the most important contributing factors to older adults’ well-being is a sense of humor. It has been defined in the literature as a cognitive ability to remember, create and understand jokes, an appreciation of humor, a tendency to laugh, a habitual cheerfulness, and a coping strategy [3].

The sense of humor has three meanings. A person is humorous if: 1- people laughed at what he/she does; 2- he/she laughs a lot and is easily amused; 3- he/she narrates funny stories and amuses others [4]. Moreover, humor refers to the willingness to experience or express what is amusing and funny [5].

There is a growing body of evidence which shows that humor improves physical and mental health, and enhances a positive worldview [6-9]. It has been considered as the most natural and cost-free method of reducing stress, anxiety, and tension. It creates psychological, emotional, and physiological changes that result in people having control over their lives [10]. The results of a study conducted by Morse et al. [11] to examine the effect of improvisation comedy on healthy older adults emerged the common themes including increased positivity, increased sense of comfort and ease with the unexpected, a sense of self-development and self-awareness, and a feeling of acceptance by their social group. The authors stated that humor combats several common geriatric conditions, such as depression, stress, and isolation. The other studies have documented that sense of humor is a health-protecting cognitive coping resource [9] that increases the probability of survival into retirement [12] and assists in the process of aging, particularly in improving health, reducing stress, and improving psychological well-being and life satisfaction among older adults [10]. The studies have examined the effect of humor on older adults, which found that humor may play a role in alleviating death anxiety [13], providing a sense of hopefulness [14], reducing pain and providing a sense of camaraderie [15], and improving older adults’ attitude about the aging process [10]. Thus, it can be found from the literature that sense of humor not only induces positive emotions, but also it may help to reduce negative emotions and stress [8].

Although the positive effect of humor on older adults has been documented by several studies, unfortunately, it should be noted that there is evidence to indicate that ability to produce, appreciate, and comprehend humor declines with age [12, 16-18]. The most important issue of humor research is that many of these studies have conducted in the cross-sectional design and conducted experimental studies did not focus on older adults.

Generally, although humor is a universal phenomenon, the way people use and express humor is strongly influenced by cultural norms, beliefs, attitudes, and values [4, 19, 20]. Thus, humor training can be influenced by culture. With regard to the positive effect of sense of humor in later life and its culture-based nature, it is imperative to find ways to maintain and improve a sense of humor. This study, therefore, has been conducted to examine humor training programs on the sense of humor among older adults.

A total of 38 community-dwelling older adults with a mean age of 67.05 years (SD=5.83) (ranging from 60 to 80 years) were included in the study as intervention and control groups.

The mean age of the participants was found to be 65.15 (SD=4.25). Intervention group consisted of 18 community-dwelling older adults (age: M = 66.50, SD = 6.14; 7 males, 11 females) and the waiting control group consisted of 20 community-dwelling older adults (age: M = 67.60, SD=5.64; 8 males, 12 females). The results of the independent t-test showed no significant difference between groups in the means of age (t(36)=-0.58, p=.568).

The sociodemographic and health characteristics of the sample by groups are presented in Table 2 The results of the bivariate analysis revealed no statistically significant difference between the intervention group and the control group in terms of age, sex, level of education, marital status, living arrangement, and chronic medical conditions (Table 2).

A series of independent-samples t-test were conducted to assess two groups at baseline regarding the sense of humor score. Table 3 shows the baseline scores on the sense of humor of the study participants. As shown in Table 3, no statistically significant difference was observed between the intervention group and the control group at baseline except for “laughing at yourself” which was higher in the control group (P ≤ 0.05).

Fig. (2). Score changes of the sense of humor and its subscales over time in both groups.

A series of paired samples t-test were conducted to evaluate the impact of the intervention on older adult’s scores on the sense of humor and its subscales. Table 4 shows the results of paired samples t-tests by study groups. As shown in Table 4, a statistically significant increase was observed in total score of sense of humor from Pre-test (M =77.28, SD = 13.62) to Post-test (M = 101.11, SD=17.06), t= -6.77, p<.001, in the intervention group. Results of other paired t-tests showed statistically significant changes from pre-test to post-test for enjoyment of humor (t= -4.59, p<.001), laughter (t= -7.83, p<.001), verbal humor (t= -4.73, p<.001), finding humor in everyday life (t= -4.19, p<.001), laughing at yourself (t= -6.36, p<.01), and humor under stress(t= -2.54, P≤.05) in intervention group. As shown in Table 4, no statistically significant changes were observed in any outcome variables from pre-test to post-test in the control group. Fig. (2) shows changes of the sense of humor and its subscales from pretest to post-test in both groups.

Additionally, a difference-in-differences analysis using an adjusted general linear model was carried out to compare two intervention and control groups in terms of a sense of humor before and after the intervention. The analysis revealed a significant increase in the sense of humor for the intervention group compared to the control group (F=43.54, p<.001), after controlling for age, sex, level of education, marital status, and chronic medical conditions. The mean score of sense of humor increased from 77.28 to 101.11 (30.8%) among the intervention group, while the average score of the sense of humor for the control group did not change substantially over time.

Humor has been conceptualized both as a cognitive ability (humor comprehension) and as an aesthetic response (humor appreciation) [24]. It has been considered a successful coping technique that can provide a more optimistic attitude towards life [25]. According to McGhee [26], humor can allow individuals to manage serious situations by redefining the circumstances as less threatening.

The current study investigated the effectiveness of the 7 humor habits on a sample of older adults in a randomized controlled trial. The intervention group received McGhee’s eight-week humor training. For the intervention group, the sense of humor increased from pre to post intervention. This indicated that the sense of humor could be malleable through a humor training program. The findings from the current study are consistent with some previous studies which found the 7HHP effectively foster humor [8, 25, 27].

In their study, Ruch, Hofmann [8] found that while the exposure to humor may increase the cheerfulness and decrease the seriousness, it cannot increase the sense of humor. In other words, unsystematic exposure to humor may result in a short-term induction of humor-related mood; it does not foster the sense of humor.

A growing body of research has documented the positive relationships between sense of humor and well-being. Individuals with a higher sense of humor are more likely to be able to reframe adverse events [25].

As people age, their cognitive abilities, such as conceptual reasoning, memory, and processing speed, gradually decline. It has been found that fluid intelligence, which refers to abilities involving executive function, processing speed, memory, and psychomotor, peaks in the third decade of life and then declines [28]. Humor requires many different cognitive functions particularly fluid cognitive abilities, which decline with age [29]. With regards to the bulk of evidence that indicates training improves cognitive function [30-32], it can be postulated that the humor training program may enhance the cognitive vitality of elderly people, consequently results in improving a sense of humor.

While several studies have documented humor as a potent predictor of life satisfaction and well-being, there is evidence indicating a sense of humor declines with age [33]. In addition to the declining humor in old age, eastern culture is less likely to use self-enhancing humor and may deprecate humor [19]. Therefore, elderly people need to be trained to enhance their sense of humor. The results of this study underline the importance of training on a sense of humor among the elderly. Our findings support the previous studies conducted by Jiang, Li [19] and Ruch, Hofmann [8] who found humor can be trained in old age and improved by standardized programs. It is suggested that the applicability of the program needs to be tested further in future studies in different settings.

Like other research, this study is not free of limitations which need to be acknowledged. Although this study attempted to use rigorous methodology, it is impossible to eliminate all threats to the study. The first limitation of this study was the relatively small sample size due to the limited number of participants per group in group therapy, which is limited to a maximum of 15 persons per group [34]. Secondly, the limitation that should be acknowledged is that only a self-report method was used to collect data, it is suggested that in the future studies, a peer-rating method will be used to complement the self-reported humor.