Association of Regular Leisure-Time Physical Activity with Happiness among Middle-Aged and Older Adults in Taiwan

The aim of the present study was to clarify the relationship between regular LTPA (i.e., 150–300 min of moderate-intensity or 75–150 min of high-intensity physical activity) and happiness among middle-aged and older adults in Taiwan. The cross-sectional study data were obtained from the Taiwan National Physical Activity Survey, a nationally representative survey of the Taiwanese population. A total of 12,687 middle-aged and older adults (45–108 years) were ultimately enrolled in this study. The questionnaire data obtained through this national telephone survey included sociodemographic characteristics, self-reported health status, self-evaluations (comprising height, body weight, and happiness), and zip code of residence. The results suggest a significant positive relationship between regular LTPA and happiness scores; that is, the middle-aged adults who engaged in more LTPA may report higher happiness occurrence than others. This study suggests that regular LTPA is an essential factor influencing happiness. LTPA is an essential form of physical activity that helps middle-aged and older people to relax.


Introduction
Happiness is a subjective mental state characterized by feelings of enjoyment and satisfaction, and it reflects the overall subjective well-being of an individual [1]. In several countries such as Canada, France, and the United Kingdom, improvements in people's overall happiness level are regarded as a sign of national progress [2,3]. Happiness also has positive effects on the long-term quality of relationships [4,5] and social interactions [6]. Moreover, in 32 countries, higher levels of life satisfaction and happiness were found to be related to lower suicide rates [7]. Higher levels of happiness are also related to lower mortality and morbidity [8,9]. The aforementioned findings constitute a part of a growing body of evidence supporting the essential role of happiness in people's health.
Leisure-time physical activity (LTPA) has beneficial effects on physical and psychological health [10][11][12]. LTPA has also been established to have positive effects on quality of life [3,13]. In addition, studies have revealed the psychological benefits of LTPA in alleviating feelings of depression and anxiety [14,15]. LTPA not only promotes life satisfaction and happiness among adults aged 18-30 years but also has a positive relationship with perceived health [16] in healthy adults [17] (Downward and Dawson, 2016) and older adults [18]. Moreover, adults who engage in more LTPA enjoy higher levels of life satisfaction, and this effect is more pronounced in older adults relative to younger adults [19].
Considering the aforementioned findings, people may be inclined to consider engaging in regular LTPA. However, Taiwan's Sports Administration [20] reported that 82.8% of the population participated in physical activity but only 33.0% regularly exercised. Studies exploring the relationship between age and happiness have produced inconsistent results; specifically, one study revealed an inverted U relationship [21] and another study discovered a U-shaped relationship, with lower physical activity levels from ages 45 to 54 but higher from ages 55 to 64 [22]. Such controversial arguments provide uncertain theories that warrant further examination. Furthermore, the association between regular LTPA and happiness has been less discussed previously. Therefore, the aim of the present study was to clarify the relationship between regular LTPA (i.e., 150-300 min of moderate-intensity or 75-150 min of high-intensity physical activity) and happiness among middle-aged and older adults in Taiwan.

Study Sample and Data Collection Procedures
The study data were obtained from the Taiwan National Physical Activity Survey (TNPAS), a nationally representative survey of children and adolescents (13-17 years), adults (18-64 years), and older adults (65 years and older) conducted by the Sports Administration, Ministry of Education, Taiwan. Enrollment was conducted through randomdigit-dialing of individuals in a sample that was proportionally stratified by age, gender, and geographical district; the enrollment protocol was implemented in accordance with that used in another study [23]. The sample population consisted of citizens aged over 13 years and was stratified by city/county (22 cities/counties in Taiwan). The sample size for each city/county was calculated to reflect that city/county's population as a proportion of Taiwan's population. The initial total sample size for the present study was 25,526, with a sampling error range of 3-5% and confidence level of 95%; hence, a sufficient sample size and statistical power were achieved. Subsequently, a computer-assisted telephone interview (CATI) was conducted from August to October 2020 by a group of well-trained and experienced interviewers, who served to ensure the quality of data collection. The questionnaire data obtained through this national telephone survey comprised sociodemographic characteristics (age, gender, education, monthly income, and occupation), physical activity behavior, self-reported health status, self-evaluations (comprising height, body weight, and happiness), and zip code of residence. A total of 12,687 middle-aged and older adults (45-108 years) were ultimately enrolled in this study. The participants were fully informed about the objective, procedures, and contents of the present study, which was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of Fu Jen Catholic University in Taiwan (FJU-IRB C109085). The participants provided oral consent prior to being interviewed. All relevant data are in a deidentified secondary dataset that has been made publicly available for research purposes.

LTPA
In the present study, regular or nonregular LTPA was determined through a series of questions during the CATI. First, the participants were asked to describe their current LTPA level. The question was as follows: "Have you participated in any LTPA in the past month?" Participants who provided a positive response were asked to describe their LTPA participation frequency and duration; the questions used were as follows: "How many times do you engage in LTPA every week?" and "How many minutes do you usually spend on each LTPA session?" Furthermore, LTPA intensity was assessed by asking the participants to describe their breathing and sweating when they were engaging in LTPA; the question asked was as follows: "When you are engaged in LTPA, you usually feel . . . ". In response, the participants structural answers such as "no changes in my breath or sweating", "I breathe faster but do not sweat", "I breathe normally but I sweat", and "I breathe quickly and sweat". Participants who reported that they usually breathed quickly and sweated were considered to have engaged in moderate-intensity LTPA. Subsequently, the participants were segmented into two groups. First, participants who participated in 150-300 min of moderate-intensity LTPA per week or 75-150 min of high-intensity LTPA per week and reported breathing quickly and sweating during LTPA were assigned to the regular LTPA group. The remaining participants were assigned to the nonregular LTPA group.

Happiness
The concepts and determinants of happiness are diverse [1,[25][26][27]. Several methods are used to measure happiness, including the Oxford Happiness Inventory [28] and Satisfaction with Life Scale [29]. Nevertheless, these methods usually use a single-item question (i.e., "Taking all things together (in general), how happy would you say you are?") to measure happiness in the LTPA domain [21,[30][31][32][33][34]. This item has been validated [35,36] and tested for its temporal stability (test-retest reliability; r = 0.86) [37]. In TNPAS 2020, happiness was measured using the aforementioned single-item question and scored on a 5-point scale from 1 ("very unhappy") to 5 ("very happy"). Furthermore, to establish binary data, the respondents were dichotomized into happy (i.e., very happy, happy, and fair) and unhappy (i.e., unhappy and very unhappy) groups according to the protocol used in another study [38].

Statistical Analysis
IBM SPSS 25.0 (IBM Co., Armonk, NY, USA) was used for this study. Student's ttest was performed to compare the continuous variables of the regular and nonregular LTPA groups. A Chi-square test was used to examine the associations between the regular and nonregular LTPA groups and the associations among their categorical variables. Multiple linear regression, with the happiness score being the dependent variable, was performed to examine the association between regular LTPA and happiness scores after adjustment for potential confounders. Unconditional logistic regression models were applied to calculate the adjusted odds ratios for happiness. Analysis results are presented herein as mean ± standard deviation or as numbers (frequency percentages). A result was considered statistically significant at a two-tailed p-value of < 0.05. Table 1 shows the research population's demographic characteristics. A total of 12,687 participants were categorized into two groups according to their engagement in LTPA. Of the participants, >20% were assigned to the regular LTPA group. Compared with the nonregular LTPA group, the regular LTPA group had a higher proportion of men (53.3%), higher percentage of participants in the normal weight range (48.8%), and higher level of education (27% received at least college education); approximately 34.9% of the participants in this group were already retired, and 75.5% self-reported that they were in excellent or good health. The two groups differed significantly in all demographic data, except for BMI.  Table 2 presents a comparison of the happiness scores of the participants in the regular and nonregular LTPA groups. Both men and women in the regular LTPA group reported higher happiness scores than did those in the nonregular LTPA group; moreover, a significant difference was observed between these two groups with respect to the happiness scores reported by the 50-54 age group (p < 0.05). Among men in the 60-64 and ≥65 age groups, a significant difference in happiness scores was observed between the regular and nonregular LTPA groups (p < 0.05). Among women in the 45-49 and 55-59 age groups, a significant difference in happiness scores was observed between the regular and nonregular LTPA groups. Significant differences were observed (p < 0.05) for all comparisons that used pooled data.  Table 3 shows a comparison of the prevalence of happiness/unhappiness between the regular and nonregular LTPA groups. In both groups, significant differences in the prevalence of happiness and unhappiness were observed among the age groups (p < 0.05). Among women in the 45-49 and 50-54 age groups, significant differences in the prevalence of happiness and unhappiness were observed between the regular and nonregular LTPA groups. Among men in the 50-54, 60-64, and ≥65 age groups, significant differences in the prevalence of happiness and unhappiness were observed between the regular and nonregular LTPA groups. Furthermore, both the regular and nonregular LTPA groups exhibited a higher prevalence of unhappiness relative to happiness. Table 4 presents the multivariate linear regression results for the happiness scores of the regular LTPA group. The results indicated a significant positive relationship between engagement in regular LTPA and happiness (p < 0.05). After adjustments for age, education, occupation, obesity status, and self-reported health status, the explanatory power of the significantly decreased for both men and women (β = 0.028 for men, β = 0.045 for women).    Table 5 provides the results from the multiple logistic regression models. The LTPA population was planned as the reference for all analyses (OR = 1.000). The results from model 2 indicated that male and female participants engaged in regular LTPA had better likelihood to report they were happy (OR = 1.216 for men, OR = 1.401 for women; p < 0.05).

Discussion
This study explored the association of regular LTPA with happiness among 12,687 middleaged and older adults in Taiwan. The results suggest a positive relationship between regular LTPA and happiness; that is, the middle-aged adults who engage in more LTPA may have higher happiness occurrence than others. In particular, in the regular LTPA group, both men and women reported relatively high happiness. In both the regular and nonregular LTPA groups, the prevalence of happiness and unhappiness was significantly different among age groups. However, in both the regular and nonregular LTPA groups, the prevalence of happiness and unhappiness was significantly different in two female age groups (45)(46)(47)(48)(49) and 50-54) and three male age groups (50-54, 60-64, and ≥65).
These findings provide evidence of how multiple factors influence the relationship between regular LTPA and happiness among middle-aged and older people. Previous studies have produced similar results regarding the association of LTPA with life satisfaction [16,19] and quality of life [39,40]. Hence, further research on the direct and indirect influence of LTPA on happiness may help clarify the discrepancies pertaining to age-and sex-related trends. Some studies have identified age as a factor that reduces LTPA [41,42], but others have suggested age to be associated with an increasing or stable trend [43] or diversification patterns of LTPA [44][45][46]. Therefore, the existence of other moderating or mediating variables cannot be ruled out.
Furthermore, in both the regular and nonregular LTPA groups, the prevalence of happiness and unhappiness did not differ significantly between the two genders. A previous study discovered gender to be associated with longer television viewing time and poorer cardiovascular health, which was observed even among participants who met physical activity recommendations; this observation could not be explained [47]. Future studies may reveal previously unknown underlying mechanisms or verify the absence of gender differences.
The strength of this study was using a huge sample size to analyze the relationship between regular LTPA and happiness among Taiwanese middle-aged adults and elders. However, there are some limitations that should be carefully addressed. First, the use of a secondary database meant that other potential confounders such as chronic diseases or mental disorders could not be considered. Furthermore, the daily activity levels were not able to take part in our analysis. Specifically, the level of activity of daily living (ADL) might be crucially confounding one's quality of late-life, as well as his/her LTPA participation. In other words, the gap may have existed in the LTPA-happiness relationship, particularly for the individuals who have a low ADL level. Therefore, future research should conduct comprehensive investigations that allow analyses of any possible confounders. Second, this study did not examine low-intensity LTPA and might have overlooked the differences engendered by LTPA of varying intensities. Third, the study used a cross-sectional design and was thus unable to verify the existence of a causative relationship. Fourth, although a huge data set was used, the data collected from the CATI was based on self-reported information. The trustworthiness of the data may not be guaranteed.

Conclusions
In summary, this study revealed that regular LTPA is an essential factor influencing happiness. LTPA is an essential form of physical activity that helps people to relax. Therefore, regular LTPA is crucial for middle-aged and older people, who should be encouraged to increase the duration and intensity of their LTPA.
Author Contributions: C.L. participated in the design, conducted the statistical analyses, interpreted the data, and drafted the manuscript. P.-L.W. helped to manage and analyze the data and assisted in data interpretation. P.-F.L. helped to revise the manuscript and assisted in data interpretation. C.-C.H. supervised the study and critically reviewed and revised the manuscript. All authors have read and agreed to the published version of the manuscript.

Informed Consent Statement:
The participants provided oral consent prior to being interviewed.

Data Availability Statement:
The design and data used in this study were approved and provided by the Sports Cloud: Information and Application Research Center of Sports for All, Sport Administration, Ministry of Education, Taiwan.