The association between social relationships and health has been extensively investigated. Social networks, and the degree to which individuals are embedded in supportive social relationships, are related to favorable health outcomes. For example, those with richer social networks have a lower risk of mortality [1
], morbidity [2
], and even functional decline [3
]. The psychological effects of social relations are also documented. Especially among older persons, informal ties such as with family members, friends, neighbors, or relatives, are important sources of well-being [1
]. In studies of social relationships and health, various measurement strategies have been used for assessing social relationships. One strategy was a quantity-based approach (i.e., number of social ties or participation in organizations), and the other was a quality-based approach (i.e., function or nature of social support). When one person interacts with another, something is exchanged. Social support refers to that something exchanged between persons. In other words, social support is embedded in people’s social networks [1
]. Social support is exchanged as a form of daily assistance, care, financial assistance, gift giving, counseling, or emotional assurance.
However, there are relatively few studies on the longitudinal effects of social support on health. Studies in the US demonstrated that instrumental support was associated with higher disability risk [7
]. Cross-sectional studies in China demonstrated a stronger association of support from spouses with well-being compared to support from children or others [9
]. A similar result has been reported in South Korea [11
]. These studies have attempted grouping social network types based on marital status, number of friends, number of children, or group participation, and found that a diverse network, characterized by the presence of both family and friends, was more beneficial for health, and a restricted network with only limited family ties was related to poor health [11
]. Although few studies assess the effect of social support on health in Asia, a study in South Korea demonstrated the longitudinal effect of social network changes on mental health [14
]. Recent Japanese studies demonstrated the protective effect of social participation on functional health among the old [4
]. However, in Asia, the longitudinal effect of social ties on disability risk remains unclear.
Cultural differences are also implicated in the association between social support and health. Cheng et al. suggested that interactions with friends are less well-being-enhancing in Asian societies than those in Western societies. This is partly explained by the relative importance of the norms of reciprocity and social harmony in Asian cultures. In such societies, the cost of seeking help from others, especially from non-family members, might be higher compared to more individualistic Western societies. In fact, the advantage observed in Western studies of non-family networks for health benefits was not detected in this study in China [13
]. In a cross-sectional study in South Korea [11
], a couple-focused network was associated with better mental health. In addition, they found more older persons were isolated compared to those in China [13
] or in Japan [15
]. In general, in studies in Asian nations, friends or neighbors were not considered to be sources of support when needs arose [16
However, recent studies in Japan suggested a health protective effect from support exchange with outside family members among the old [9
]. Due to a rapid decline in traditional family systems, the number of older persons living alone is on the rise in Asian nations. Japan is no exception. Household size is getting smaller, as in other industrialized nations, and more adult children live separately from their parents once they get married [16
]. According to the annual report released by the Cabinet Office of Japan for the fiscal year 2014, 23.3% of households with persons aged 65 and over were one-person households [18
]. This might lead to a shifting importance toward more diverse social networks including non-family members among the old. Thus, we expect that, in present day Japan, the health protective effect from non-family ties would be observed independent of family ties. Since the longitudinal effect of support from non-family members remains unclear, we attempt to fill the knowledge gap by assessing this effect, using public insurance data maintained by local governments in Japan.
In this study, we analyzed the association between social ties, assessed by social support exchange and onset of functional disability, using 10-year follow-up data. Our aim was to investigate the relative effect of ties with family or relatives (co-residing, or living apart) compared to ties with non-family members (friends or neighbors) on the functional health of older persons in Japan.
2. Materials and Methods
2.1. Data and Participants
The present study is a part of the Aichi Gerontological Evaluation Study (AGES) Project. This is a community-based prospective cohort study in Japan in which investigators evaluated factors associated with incident functional disability among non-institutionalized older people aged 65 years or above. The baseline survey was conducted in October of 2003. Questionnaires were sent to a random sampling of community-living older adults aged 65 years or older in six large municipalities and a complete census from four smaller cities. A detailed description of the study population and the baseline survey has been published [19
]. Study participants were comparable to entire older Japanese populations in terms of age and sex. Detailed descriptions of questions on the survey were also published [20
After excluding those with incomplete data on sex and age, 15,313 people (7381 men and 7932 women) were introduced into the cohort and followed for 10 years from 1 November 2003 to 28 March 2013, using the Long-term Care Insurance (LTCI) system database maintained by local governments. Japan’s LTCI system is a government-operated national insurance system for long-term care and was introduced in April of 2000, to allow every Japanese person aged 65 and older with functional limitations or dementia access to care for basic activities of daily living [21
]. Since receipt of benefits under this LTCI system is on an application basis, some people do not receive benefits despite being dependent for activities of daily living for various reasons, such as the availability of family members to provide care or financial burden, since a 10% co-insurance is required to use services under the LTCI. Thus, we asked about basic activities of daily living, such as using the toilet, bathing, or transferring, in the survey of 2003 to eliminate those already functionally dependent as a baseline. Those with missing data in their activities of daily living were also eliminated. This procedure left 14,088 older people or, 92% of the total sample of this cohort for the analyses. The study protocol and informed consent procedure were approved by the Ethics Committee in Research of Human Subjects at Nihon Fukushi University (#10-05).
2.2. Incident Disability
We obtained information regarding certification of long-term care needs, death, and relocation of participants (e.g., moving out of the study area) from the LTCI system database. We defined people with functional disability as those who became eligible for care under the LTCI during the 10-year follow-up. In this system, certification of long-term care needs was based on an evaluation of each applicant’s degree of physical and mental disability, determined by a home-visit interview and a diagnosis from the primary care physician. A municipality certification committee determines the eligibility for receiving services [21
2.3. Explanatory Variables
To elucidate social ties in this study, we asked respondents about five types of social support with persons in the three social network categories of co-residing family, family and relatives living apart, and friends and neighbors. “Family” refers to a spouse or partner, children, siblings, older parents, and other relatives. Types of support were emotional (providing/receiving), instrumental (providing/receiving), and appraisal (receiving). “Listening to concerns and complaints” was regarded as emotional support and “looking after when sick in bed for a few days” as instrumental support. Appraisal support was elicited by asking, “Do you have someone who acknowledges your existence and value?”
We considered that respondents had social ties when at least one person was giving or receiving any of above five types of support in specific network category. Social ties in each network category were then dichotomized as “having ties” (coded 1) or “not having ties” (coded 0). Our main aim was to study the relative effect of social ties in three different social network domains. Thus, we dichotomized social ties in each network category to calculate the relative risk of disability. In other words, we wanted to know what happens to a person with no ties, exchanging no support, with family members.
Controlling variables were age in years, health status, and living arrangement. Age and health status are important confounders when assessing the relationship between social ties and incident disability [1
]. Health status was elicited by asking whether the participant was under medical treatment or not. We asked, “Are you currently receiving any medical treatment?”. The answering categories were, “I have no illnesses or conditions”, “I have illnesses or conditions but need no treatment”, “I discontinued treatment on my own decision”, and “I am currently receiving medical treatment”. Living arrangement in five categories, alone, only with spouse, with spouse and children, no spouse with children, other, was treated as a covariate. In sub-analyses, we analyzed the data by stratifying those living alone and those living with someone. The direction of the association between social ties and functional decline was the same. Moreover, in our sample, 6.5% of men and 10.9% of women did not have anyone with whom to exchange support despite living in the same house. Thus, instead of analyzing data by stratifying those living alone and those living with someone else, we treated living arrangement as it was, as studies suggested that loneliness has a stronger effect on health [1
]. Our underlying assumption was that being isolated psychologically rather than living alone, per se, had higher risk for functional decline.
2.5. Statistical Analyses
Age-adjusted cumulative incidence of functional decline was calculated using a general linear model for each covariate. A Cox hazard proportional model stratified by sex was employed to calculate hazard ratios for functional decline since sex differences were observed in the associations of social relations and health in previous studies [1
]. Those who died or moved away from the study site during the follow-up period were considered as censored cases.
To test whether the effects of each factor were independent from the influence of the others, we used hierarchical regression modeling procedures. First, we constructed a model adjusted for age in years and living arrangement to predict incident disability. Then, we added health status in the second model to consider the effect of ill health on need-driven cohabitation. “Need-driven” means those who need support due to ill health are more likely to live with family members, especially with adult children [16
]. Finally, we entered all social ties in the three network categories simultaneously along with age, living arrangement, and health status to evaluate the independent effect of each social tie.
We used SPSS 21.0J (SPSS, Chicago, IL, USA) for statistical analysis. A p-value of less than 0.10 was considered marginally significant, and a p-value less than 0.05 was considered statistically significant.