Article

Active Social Participation and Mortality Risk Among Older People in Japan: Results From a Nationally Representative Sample

Research on Aging 2015, Vol. 37(5) 481–499 ª The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0164027514545238 roa.sagepub.com

Yuka Minagawa1 and Yasuhiko Saito2

Abstract A large literature suggests that active social participation contributes to the well-being of older people. Japan provides a compelling context to test this hypothesis due to its rapidly growing elderly population and the phenomenal health of the population. Using the Nihon University Japanese Longitudinal Study of Aging, this study examines how social participation, measured by group membership, is related to the risk of overall mortality among Japanese elders aged 65 and older. Results from Cox proportional hazards models show that group affiliation confers advantages against mortality risk, even after controlling for sociodemographic characteristics, physical health measures, and family relationship variables. In particular, activities geared more toward self-development, such as postretirement employment and lifelong learning, are strongly associated with lower levels of mortality. Findings suggest that continued social participation at advanced ages produces positive

1 2

Sophia University, Tokyo, Japan Nihon University, Tokyo, Japan

Corresponding Author: Yuka Minagawa, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo, 102-8554, Japan. Email: [email protected]

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health consequences, highlighting the importance of active aging in achieving successful aging in the Japanese context. Keywords social participation, aging, mortality, older adults, Japan

Introduction As the world’s elderly population grows and an increasing number of people now expect to remain productive and engaged well into their golden years, the term active aging has gained wide usage at the international level. According to the World Health Organization (2013), active aging refers to ‘‘the process of optimizing opportunities for health, participation and security in order to enhance quality of life as people age,’’ foregrounding the importance of continued engagement in social, economic, and cultural affairs at advanced ages. Using the concept of active aging, this study examines the impact of active social engagement, measured by group affiliation, on the risk of overall mortality among older Japanese men and women between 1999 and 2009. Due to its rapidly graying population and the phenomenal health of the population, Japan offers an excellent opportunity to test the idea of active aging. By using a large nationally representative sample, employing a longitudinal study design, and focusing on the types of activities that individuals pursue, this research contributes to the existing literature on the health effects of social participation in later life. Integrating the Japanese case into research serves as guidance for future social policy in other countries that will soon be faced with the challenge of aging.

Social Participation at Advanced Ages in the Japanese Context Japan leads the world in terms of population health status. First and foremost, men and women in Japan have one of the highest life expectancies in the world. The most recent figures, for 2012, show that male life expectancy at birth was 79.94 years, while female life expectancy reached 86.41 years (Ministry of Health, Labour and Welfare, 2013). In addition, Japanese people have the longest healthy life expectancy (HALE) at birth, denoting the number of years in which people can expect to live in good health. In 2010, HALE at birth was 70.6 years for men and 75.5 years for women (Salomon et al., 2012). Second, the Japanese population is aging at an extraordinary

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pace due to low levels of fertility and mortality. The proportion of the population older than 65 has increased from 17.4% to 25.1% between 2000 and the present and is expected to reach approximately 40% in 2060 (Cabinet of Office of Japan, 2013). The number of individuals aged 75 and above is rapidly growing in a phenomenon known as cho-koreika (hyperaging). These observations illustrate the outstanding health status of Japanese people, including the elderly population. Japan’s growing number of healthy elders has promoted ‘‘active aging’’ initiatives in the nation, making Japan a useful bellwether for understanding relationships among health, age, and activity on a larger scale. In 2001, the Cabinet Office of Japan launched ‘‘General Principles Concerning Measures for the Aging Society.’’ This program seeks to create a social environment in which older people can live with ikigai: ‘‘that which most makes one’s life seem worth living,’’ according to Matthews’ (1996, p. 718) translation. A particular emphasis is placed on social participation as a core element of aging well. There are various programs and measures to help Japanese elders continue to have ikigai in later life. The Silver Human Resource Centers (SHRCs), for instance, offer part-time paid work for those who wish to remain employed after retirement. The center’s major role is to place men and women aged 60 and older within temporary employment in departments of local governments or business (Weiss, Bass, Heimovitz, & Oka, 2005). SHRC employment includes outdoor work (e.g., cleaning up streets and parks), facility administration (e.g., administering car and bicycle parking lots), and office work (e.g., reception work; Bass & Oka, 1995). In addition to postretirement employment, there is a rising interest in personal development at older ages through continued education. The concept of lifelong learning is based on United Nations Educational, Scientific, and Cultural Organization’s declaration that education should be a lifelong process for all (Williamson, 1997). In Japan, the ‘‘Lifelong Learning Promotion Law’’ was introduced in June 1990 to enhance learning in later life, and a number of organizations offer educational opportunities for older citizens. While postretirement work and continued learning focus on selfdevelopment, other groups provide older individuals with opportunities to stay connected with the outside world. Chonaikai, neighborhood associations, are important for urban social life in Japan. Chonaikai, composed of all the households in the neighborhood, primarily have political and administrative functions, such as delivering notices from the municipal government to residents (Matsumoto, 2000). Socially, chonaikai help Japanese city dwellers develop and maintain a sense of community and solidarity (Bestor, 1985). Chonaikai sponsor neighborhood-level activities for local

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residents, particularly for older people. One such important activity is the celebration of the Respect for the Aged Day in September. Further, senior citizens’ clubs (rojin clubs in Japanese) promote active lifestyles among older people through a range of group activities, such as singing and crafting. Overall, Japanese elders have access to various forms of social participation, ranging from activities toward self-realization (e.g., part-time work after retirement or later life learning) to those toward maintaining ties with others (e.g., chonaikai or rojin clubs).

Social Participation and Elderly Well-Being There is a well-established literature in the fields of gerontology, sociology, and demography on the physical and mental health benefits of active social participation: More socially active individuals are at lower risk of death, physical health problems, and psychological distress compared to those who are socially isolated (for a comprehensive review, see Berkman, Glass, Brissette, & Seeman, 2000; House, Landis, & Umberson, 1988). Further, social integration yields particularly strong health consequences to older adults (Musick & Wilson, 2003). Individuals are likely to experience social withdrawal as a result of retirement and a loss of meaningful relationships as they age (Mirowsky & Ross, 2003). Being part of a community or social group facilitates access to social resources, including emotional and material support, reduces feelings of powerlessness or dislocation, and fosters a sense of purpose in life, thereby contributing to the physical and psychological well-being of older people (Harris & Thoresen, 2005; Musick & Wilson, 2003). Research in the United States, for example, indicates the protective effects of group membership against mental health problems (Musick & Wilson, 2003; Thoits & Hewitt, 2001), institutionalization (Steinbach, 1992), and death (Harris & Thoresen, 2005; Musick, Herzog, & House, 1999). A crossnational study by Engelhardt, Burber, Skirbekk, and Prskawetz (2010) shows that active social participation, such as attending educational courses, going to sports clubs, and doing charitable activities, is associated with improved cognitive performance across 11 European countries and Israel. In non-Western countries, social networks outside the household are related to lower levels of depressive symptoms, as in Chan, Malhotra, Malhotra, and Østbye’s (2011) findings for Singaporeans aged 60 and older, and membership in volunteering groups is predictive of better self-rated health status among older people in the Republic of Korea and Fiji (Su & Ferraro, 1997). Overall, these research findings offer strong cross-national evidence to suggest the health benefits of active social participation in later life.

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Contributions of the Present Study Although the positive impact of being socially active at older ages has been reported in many parts of the world, relatively few studies have focused on Japan. The small body of research that does explore the relationship between social participation and health has left several important issues unaddressed. We highlight four general weaknesses of this body of work. The first is that of generalizability. Iwasaki et al. (2002) find that group affiliation (e.g., hobbies and club activities) is associated with lower levels of overall mortality among men and women in Japan. Yet, their sample is taken from only two cities in Gunma Prefecture. Similarly, analysis by Murata et al. (2005) shows a negative relationship between social integration and the risk of mortality among men and women aged 65 and above, but the sample is restricted to those living in one rural town in Nagano Prefecture. Thus, due to geographic limitation, it remains an open question as to the extent to which we can generalize the results of these studies. Second, social participation has not been analyzed as the dependent variable. Instead, scholars most often look at it either as an independent variable (Iwasaki et al., 2002; Murata et al., 2005; Sugisawa, Liang, & Liu, 1994) or as one of the controls (Tiedt, 2010). Consequently, there remains a weak understanding of factors that lead individuals to be socially active. Some factors may influence both social participation and health and thus observed associations between social integration and health may be spurious in some cases (House et al., 1988; Musick & Wilson, 2003). Fully understanding the health consequences of social integration requires research that examines factors associated with these two outcomes. Third, social participation cannot occur without social relationships: Social participation may be fostered or restricted by interpersonal relationships, roles, and obligations that individuals already have (House et al., 1988; Musick & Wilson, 2003). This is of particular importance in the case of Japan, since traditional Japanese families follow a stem structure, in which older parents live with their sons and daughters. Although the number of multigenerational households has decreased over time, the extended family structure remains predominant in Japan (Takagi & Silverstein, 2006). However, limited attention has been paid to relational contexts in testing the health impact of social involvement in Japan. Finally, we must focus on the kinds of activities that individuals pursue. Prior research examines the influence of group membership on health but combines different types of activities into a single large entity, ‘‘social participation’’ (e.g., Murata et al., 2005; Sugisawa et al., 1994). There is indeed

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reason to expect that group membership may have different impacts on health by types and purpose of activity. Health consequences, for example, might differ for activities that simply require membership, namely chonaikai, versus for those requiring increased physical activity, such as sports clubs and SHRCs employment. It is therefore important to consider the kinds of activities people engage in as a form of social participation. Using a large nationally representative sample of Japanese elders and multivariate methods with appropriate statistical controls, this research investigates the association of social participation with the risk of death among Japanese elders between 1999 and 2009. This study addresses three questions raised by previous theoretical and empirical work on this topic: (1) What are the sociodemographic factors associated with active social involvement among the Japanese elderly? (2) How is group membership related to the risk of mortality among older men and women in Japan? and (3) Do health consequences differ by type of activity?

Method Data and Sample The data for the current analysis come from the Nihon University Japanese Longitudinal Study of Aging (NUJLSOA). The NUJLSOA is designed to monitor the health status of the Japanese elderly and has been conducted 5 times: Wave 1 (1999), Wave 2 (2001), Wave 3 (2003), Wave 4 (2006), and Wave 5 (2009). The survey was administered throughout Japan via a multistage sampling method, and it is representative of the Japanese population aged 65 and older at the baseline survey year of 1999. The study included community living residents and oversampled those aged 75 and older to closely analyze the older segment of the population. More detailed information about our data can be found at the NUJLSOA website http://gero.usc. edu/cbph/nujlsoa/ To observe changes in key variables between each of the waves, the data were pooled across the four observation periods (i.e., 1999–2001, 2001–2003, 2003–2006, and 2006–2009). The initial year of each interval is considered as the baseline and the ending year is treated as the follow-up. In the end, data from each interval were pooled for analysis. Drawing on prior research that has used interval observations of NUJLSOA data (Chan, Zimmer, & Saito, 2011; Takagi & Saito, 2013), this study employs the same analytical strategy and examines the relationship between group membership and mortality over the 10-year period (for more details of the method, see Hayward,

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Crimmins, & Saito, 1998). Our analysis is based on a total of 13,225, and over the entire observation period for all respondents, 1,434 deaths occurred among those observed to be alive at the beginning of the interval. It is important to note that longitudinal analyses often confront problems of data loss over time as a result of attrition (Singer & Willet, 2003). In total, 2,451 study observations were lost between 1999 and 2009. We found significant differences between observations included in the analyses and those out of the sample. In order to account for differences between these two groups, we created a weight adjusted for the probability of loss to follow up based on sociodemographic characteristics, such as age, gender, and marital status. Since using the adjusted weight did not largely alter the results of present analyses, we report the findings using an initial probability weight for the representativeness of the sample (the weighted results are available upon request). Concerning the observations with missing values, household income had the highest level of missing data (17.99%). Therefore, we used mean household income to fill missing values and included a dummy variable for missing responses of this item. The rest of the variables had missing data of less than 6% and were dropped from the analysis.

Measures The main independent variable we consider is group affiliation at baseline. Respondents are coded 1 if they belong to at least one of the following groups: chonaikai, neighborhood associations; keirokai, respect for the aged associations; fujinkai, women’s clubs; rojin clubs, senior citizens’ clubs; educational, hobby, and sports circles; volunteering groups; SHRCs; religious organizations; and something else. Further, in order to determine whether health consequences differ by type of activity, we created a dummy variable for self-development activity (1 ¼ belong to SHRCs or educational, hobby and/ or sports circles; 0 ¼ otherwise). Note that, while there are no clear conceptual guidelines as to how to define different types of activities, this study takes a speculative step by focusing on those geared more toward personal growth. Research has suggested that motivations for social activities involve both expressive (e.g., personal satisfaction or social network building) and instrumental dimensions (e.g., career advancement or skills building; Leung, Lui, & Chi, 2006). The current project employs this conceptual framework and focuses on the instrumental aspect of social participation. To best isolate the influence of social participation on mortality risk, the following sociodemographic factors are included in the analysis as controls: gender (1 ¼ male), age (continuous in years), marital status (1 ¼ currently

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married), educational attainment (1 ¼ more than high school education), and higher income (1 ¼ higher than the 50th percentile). We also controlled for physical health status variables. General health status is self-reported as very good (referent), good, fair, bad, and very bad. Physical impairment is a count of difficulties in activities of daily living (ADLs). Further, to account for the potential influences of relational contexts on individuals’ chances of social participation (House et al., 1988), we include the following variables: the number of immediate family members (continuous), provision of support to children (1 ¼ provided instrumental or emotional support to children), and receipt of support from children (1 ¼ received instrumental or emotional support from children).

Analytical Strategy The current analysis has two parts. The first part is based on logistic regression and identifies sociodemographic factors associated with social participation among Japanese elders, using any membership and membership in selfdevelopment activities as the dependent variables. The second part of the analysis uses Cox proportional hazards models to examine the relationship between social participation and mortality risk between 1999 and 2009. Group affiliation and all control variables are measured at baseline (i.e., at the beginning of each interval), whereas mortality is measured at follow-up (i.e., at the end of each interval). Thus, status changes between the beginning and the end of each interval are used to determine the hazard of experiencing a death. The first model contains only membership variables at baseline (Model 1), and theoretically important factors are included in Model 2. Our goal is straightforward, that is, to identify how social participation is associated with the risk of death (Model 1) and then to determine whether the effect of active social involvement is reduced after introducing control variables into the model (Model 2). Statistical analyses were conducted in Stata12.0 (2011).

Results Table 1 presents the frequency distributions of social participation, sociodemographic characteristics, health status measures, and relational variables. Chi-square tests were conducted to determine whether there were statistically significant differences between study sample observations and those classified as being dead. There are some striking differences in the distributions of the variables by survival status. In this sample, survivors were more

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Table 1. Frequency Distributions for Social Participation, Sociodemographic Factors, Health Status, and Relational Contexts in the Nihon University Japanese Longitudinal Study of Aging (NUJLSOA), 1999–2009.

Social participation Any affiliation Self-development activity Sociodemographic factors Male Age (mean) Married High school education Higher income Health status Self-reported health status (1–5, mean) Physical impairment (mean) Relational contexts Number of family (mean) Provide support to children Receive support from children

Alive (1)

Dead (2)

Difference (3)

61.98 19.41

35.73 6.63

*** ***

42.84 76.74 58.30 37.29 43.95

50.49 82.28 49.23 25.79 42.39

*** *** *** *** —

2.82 1.41

3.31 2.24

*** ***

3.24 34.19 42.97

3.47 28.16 54.53

— *** ***

Note. Columns 1 and 2 present proportions for categorical variables and mean values for continuous variables. Column 3 summarizes statistical significance for differences between survivors and decedents. All the variables were measured at the beginning of each interval. ***p < .001.

socially active compared to decedents: 61.98% of survivors belonged to at least one social group between 1999 and 2009 and 19.41% of them engaged in some kind of self-development activity. Survivors were also younger, were more likey to be currently married, and had higher educational attainment. Survivors had better physical health status, characterized by better self-rated health status and less restrictions on physical functioning. Additionally, they were less likely to receive emotional or instrumental support from children, but they were more likely to help children. The results of the logistic regression analyses illustrate several key predictors of group membership among older men and women in Japan (Table 2). As shown in Model 1, higher income (odds ratio [OR] ¼ 1.21, p < .001) and receiving support from children (OR ¼ 1.19, p < .001) are strongly associated with higher odds of joining at least one social group. Physical health problems, measured by self-rated health and difficulties in ADLs, reduce the odds of being socially active. Model 2 focuses on the kinds of activities that individuals pursue. Perhaps the most interesting finding follows from significant

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Table 2. Odds Ratios for Group Membership in the Nihon University Japanese Longitudinal Study of Aging (NUJLSOA), 1999–2009.

Sociodemographic factors Male Age Married High school education Higher income Income missing Health status Self-reported health status Very good Good Fair Bad Very bad Physical impairment (count) Relational contexts Number of family Provide support to children Receive support from children Number of observations

Any affiliation (1)

Self-development (2)

1.03 1.00 0.91 1.01 1.21*** 0.67***

0.98 0.97*** 0.73*** 1.65*** 1.51*** 0.65***

ref 1.08 0.86** 0.67*** 0.33*** 0.82***

ref 1.00 0.82** 0.49*** 0.21*** 0.73***

1.03 1.16* 1.19*** 10,804

.98 1.10 .85** 10,874

Note. Column 1 presents the odds of group affiliation of any kind, and column 2 presents the odds of engaging in self-development activities, such as postretirement employment or educational circles. Group affiliation and all the control variables were measured at the beginning of each interval. *p < .05. **p < .01 ***p < .001.

differences in the socioeconomic determinants of membership by the context of activity. For example, high school education does not have a significant relationship with group affiliation in Model 1, but it is a powerful predictor of self-development activities (OR ¼ 1.65, p < .001), suggesting that high school graduates tend to choose activities related to personal growth. Interestingly, age and being married are inversely associated with the odds of engaging in self-development activities (OR ¼ .97 and OR ¼ .73, p < .001). Also, receiving emotional or instrumental support from children is related to lower odds of engaging in self-development activities (OR ¼ .85, p < .01). Table 3 displays hazard model estimates for the relationship between group affiliation at baseline and all-cause mortality at follow-up among Japanese elders. We first focus on models using any group affiliation as the

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Table 3. Hazard Ratios of Mortality in the Nihon University Japanese Longitudinal Study of Aging (NUJLSOA), 1999–2009. Any affiliation (1)

Social participation Any affiliation (¼ 1) Self-development (¼ 1) Sociodemographic factors Male Age Married High school education Higher income Income missing Health status Self-reported health status Very good Good Fair Bad Very bad Physical impairment (count) Relational contexts Number of family Provide support to children Receive support from children Number of observations

Self-development (2)

Model 1

Model 2

Model 1

Model 2

0.56***

0.73*** —

— 0.48***

— 0.77**

1.98*** 1.10*** 0.88 0.87 0.91 1.29*

1.92*** 1.10*** 0.89 0.89 0.90 1.28*

ref 1.26 1.41** 2.27*** 3.93*** 1.14***

ref 1.26 1.41** 2.29*** 4.09*** 1.15***

1.02 0.84**

1.02 0.83**

10,804

10,874

Note. Column 1 uses any affiliation as the independent variable, and column 2 uses membership in self-development activities as the independent variable. Group affiliation and all the control variables were measured at the beginning of each interval. *p < .05. **p < .01. ***p < .001.

independent variable. Two important findings emerge from the analyses. First, as shown in Model 1, group membership is inversely associated with the hazard of mortality among older men and women in Japan. Those who belong to at least one social group are 44% less likely to die during the study period compared to those who do not belong to anything (hazard ratio [HR] ¼ .56, p < .001). Second, the protective effect of group affiliation against mortality risk continues to be strong, even net of all controls (Model 2). The relationship between group membership and mortality risk was slightly attenuated by the inclusion of sociodemographic characteristics,

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health status, and role context variables (HR from .56 to .73), but the result remains statistically significant at the .001 level. These results elucidate strong associations between group membership and the risk of mortality among older adults in Japan. The second set of analyses in Table 3, which focuses on the kinds of activities, again highlights the importance of social participation in shaping individuals’ mortality risk. Among Japanese men and women aged 65 and older, those who engage in self-development activities, such as postretirement employment and lifelong learning, are 52% less likely to die during the study period compared to those who do not (Model 1, HR ¼ .48, p < .001). Further, the relationship between mortality and self-development activities continues to be significant, net of all the theoretically important variables (Model 2). Even after adjusting for sociodemographic, physical health, and relational factors, self-development activities predict mortality risk (HR ¼ .77), and the results remain statistically significant at least at the .01 level. In short, these findings suggest that social participation, defined here by group membership, has a strong relationship with the risk of mortality among Japanese elders above and beyond effects due to potential confounders. Next, we look at the effects of sociodemographic characteristics, physical health conditions, and relational factors on mortality. Males have significantly higher levels of mortality compared to their female counterparts, and mortality risk increases just over 10% for each additional year of age. These results are consistent with many previous studies (for review, see Rogers, Everett, Onge, & Krueger, 2010). As expected, poor physical health status is a strong predictor of mortality. For instance, very bad self-rated health is related to almost 4 times the hazards of dying during the study period compared to very good health. Similarly, physical impairment is associated with increases in mortality risk. Interestingly, providing support to children confers advantages against mortality risk, whereas receiving support is not strongly related to the hazard of death in this sample.

Discussion In this article, we used five waves of the NUJLSOA (1999–2009) and tested how social participation is related to mortality risk among Japanese men and women aged 65 and above, with a special focus on group affiliation. This research improves upon previous studies by using nationally representative data on the Japanese elderly, investigating the sociodemographic determinants of active social involvement, accounting for relational contexts in

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which social participation takes place, and focusing on the types of activities that individuals pursue. The empirical information provided in this study allows several important conclusions to be drawn. First, we find some factors predictive of active social participation among Japanese elders. Sociodemographic factors have different impacts on group membership, and the association further depends on types of activities. People with higher socioeconomic status, namely higher levels of educational attainment, tend to join groups geared more toward personal development, such as postretirement part-time work and continued learning, whereas, older and married individuals have lower odds of engaging in such activities. Also, physical health problems are related to lower odds of social involvement of any kind. Analysis by Raymo, Liang, Kobayashi, Sugihara, and Fukaya (2008) indeed shows the strong influence of physical health conditions on retirement decisions among Japanese men. Thus, these results suggest that impaired mobility seems to hinder Japanese elders from staying socially active. Interestingly, receiving emotional or instrumental support from adult children is related to higher odds of being affiliated with at least one group, but it is predictive of lower odds of participating in self-development activities. These results raise the possibility that those who receive support from their children are likely to be physically or cognitively impaired, and thus they might find it challenging to engage in self-development activities, such as postretirement employment and continued learning. Taken together, these findings indicate that types of social participation seem to be influenced by individuals’ structural positions, resources, and physical health conditions. Scholars have less often looked at social participation as the dependent variable, and relatively little is known about factors that prompt continued engagement in society at older ages. This research represents an important first step toward understanding the context of active social participation in Japanese society. Second, our results provide clear evidence suggesting the physical health gains of active social participation among Japanese elders. Group affiliation confers substantial and significant advantages against the risk of mortality among Japanese adults aged 65 and over, even net of sociodemographic factors, functional health measures, and family relationship variables. Therefore, active social involvement is related to the risk of death beyond and above well-known predictors of mortality. The positive health consequences of active social involvement have been documented in a number of countries, but Japan is particularly unique, in that the country has one of the fastest growing and healthiest elderly populations in the world. Our findings add to the extant literature by demonstrating that active social involvement

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remains as a powerful predictor of mortality in a demographically unique environment such as Japan. Third, activities toward personal growth strongly predict the risk of death. Those who belong to educational, hobby, and sports circles, or short-term employment, display significantly lower hazards of death compared to those who do not during the study period. The protective effects of selfdevelopment activities remain strong even after adjusting for a range of control variables. We conducted supplemental analyses to include rojin clubs into the self-development category, but the substantive conclusions of this study remain the same with or without rojin clubs. Further, we reestimated all models with a different age range. The protective effect of selfdevelopment activities disappeared when the sample was limited to those aged between 65 and 80. In contrast, the effect continued to be significant among those aged 80 and older. These results indicate that selfdevelopment activities offer significant advantages against the risk of mortality particularly for the oldest old. Past studies most often use the single large category ‘‘social participation’’ and then test its relationship to physical and mental health outcomes (Murata et al., 2005; Sugisawa et al., 1994). Although the classification of activities in this study is crude, this research instead focuses on the kinds of activities individuals engage in, and it elucidates how health consequences might vary by type of activity. Overall, these results confirm the strength of active social involvement in later life as a predictor of subsequent mortality risk among older men and women in Japan. Scholars have long been interested in the health consequences of social participation, but little attempt has been made thus far to fully test this hypothesis in the Japanese context. The major strengths of our study include the use of a large nationwide longitudinal data set, the exploration of the determinants of social participation, and the statistical analysis of the impact of active social involvement on the risk of overall mortality. Further, this work extends the existing literature by focusing on an overlooked aspect of social participation, that is, the kinds of activities individuals pursue. Although suggestive, our results should be interpreted in light of the study’s limitations. First, this study focuses only on group membership and, thus, does not consider levels of commitment. Musick, Herzog, and House (1999) demonstrate that volunteering in moderate amounts (in their study, less than 40 hr per week) produces the lowest risk of mortality among older people in the United States. Also, previous studies have used the Berkman– Syme social network index, including marital status, social contacts, and group affiliation, as an indicator of broader social relationships (Berkman

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& Syme, 1979). The NUJLSOA, however, does not include questions about the amount or frequency of social activity or contacts, making it difficult to construct a similar index in the present analyses. Therefore, due to data constraints, our work focuses only on membership in social groups. More information is needed to identify specific mechanisms linking social participation to improved health among older adults. Second, our approach toward different types of social groups is only speculative. In this study, we roughly divide groups into self-development activities and community activities, rather than testing how membership in each group is related to mortality. Given that the majority of respondents were affiliated with more than one group, without detailed information about activities, namely levels of commitment, it is difficult to elucidate the mortality effect of a specific group. With all that said, since previous research findings show that health consequences differ by kind of activity (Moen, Dempster-McClain, & Williams, 1989; Musick et al., 1999), more precise distinctions between social activities should be explored in further research. Finally, although the current models include a wide range of control variables, there might be other factors linking social participation to mortality risk. Previous studies, for instance, have suggested depressive symptoms as an important factor impacting the health status of Japanese elders (Tiedt, 2010). We adjusted for the Center for Epidemiologic Study–Depression scale at baseline, but the results of this study remained almost unchanged. Further, according to Wilson, Mendes de Leon, Bienias, Evans, and Bennett (2004), personality is an important predictor of mortality in old age. Exploring possible confounding variables between social participation and mortality risk is a fruitful avenue for future research.

Conclusion The central implication of this study is that active aging is the key to achieving successful aging in Japan. This point is particularly important for Japanese public health policy. The Japanese government has addressed challenges posed by its growing elderly population, as in the implementation of the national long-term care insurance (LTCI) law (Kaigo Hoken Ho) in April 2000. The new law brought about fundamental changes to the traditional Japanese reliance on familial in-home care, which can burden family caregivers physically and psychologically (Lahaie, Earle, & Heymann, 2013). The LTCI law is innovative, in that it covers both home-based and institution-based care services and seeks to lessen the burden of elderly care on family members (Yong & Saito, 2012). While Japan has developed a

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system of comprehensive public long-term care, promoting active lifestyles among older people, as this study suggests, might be as important as providing instrumental support in shaping their physical health status. Analysis by Weiss, Bass, Heimovitz, and Oka (2005) finds that older men who actively work at SHRC jobs enjoy higher levels of ikigai compared to those who do not. In fact, it has been reported that continually receiving help from caregivers increases a sense of dependency, lowers self-esteem, and elevates the risk of psychological distress (Mirowsky & Ross, 2003). Therefore, active social involvement might contribute to improved health, longevity, and emotional well-being among older men and women in Japan. The present findings substantively contribute to the body of work investigating the phenomenal health status of the Japanese people. Researchers have long been interested in Japanese longevity, but the mechanisms of the phenomenal health of the Japanese people remain to be firmly established. While past research has tended to focus on biological and functional factors, such as biomarkers (Crimmins, Vasunilashorn, Kim, Hagedorn, & Saito, 2008), blood pressure (Davarian, Crimmins, Takahashi, & Saito, 2013), and obesity (Reynolds et al., 2008), this study brings new evidence to bear on this topic: Social factors might be just as important as individual characteristics in the production and distribution of health. Overall, in the face of the rapidly aging population, more research and policy attention should be directed toward the social and cultural circumstances in which older individuals are embedded. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported in part by Grant-in-Aid for Scientific Research (25293121) from the Japan Society for the Promotion of Science.

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Author Biographies Yuka Minagawa is Assistant Professor at Sophia University. Her research focuses on differentials in health and mortality across populations groups in Europe and Asia. Her current research considers how political, economic, and social environments influence the health status of populations in the former communist countries in Eastern Europe. Yasuhiko Saito is Professor at Nihon University Advanced Research Institute for the Sciences and Humanities. His research interests include health expectancy and aging. Over the last fifteen years, he has conducted a six-wave national longitudinal survey on aging and health in Japan.

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