In this study, we investigated whether the association between social support and mental health varied in different aging stages in relation to objects by integrating sub-dimensions of support such as functions and roles. Our results demonstrated different patterns within three categories of objects; either ESS or ISS from or to community neighbors showed a positive relationship with mental health whereas supportive interaction with kin or friends, as the main objects in a supportive social network among the older people, may lose its positive relation with mental health when it comes to specific subscales of social support (kin: provided ESS; friends: provided ESS or received ISS). Association between social support and mental health varied by the two age groups suggesting social support potentially related to the mental health status of pre-old age rather than the old age respondents. Our analysis showed a different association between specific objects and mental health, which was a novelty of our investigation for filling the blank of existing literature, considering available present publications barely discussed the social supports from the view point of those objects. We will discuss our findings regarding the three object categories respectively as follows.
Firstly; Models 1 in Table 3, Table 5 and Table 6 illustrated beneficial results from social supportive interaction with family and relatives, especially in terms of instrumental social support. Previous reports have shown that perceived support from family has a positive relationship [22], especially one’s spouse for married people and children for people living without a spouse [21, 23]. Secondly; our analyses demonstrated that a supportive connection with friends had a positive result on mental health (Models 2 in Table 3 & Table 6), which was in accordance with previous researches [7, 23]. However, our results show that the relationship only happened when it was received ESS or provided ISS, which suggests a preference for taking less and giving more to friends. This may be influenced by Japanese culture which values being modest and not bothering others; however, further research is needed to clarify the mechanism.
Thirdly; while previous reports were limited to the level of friends or family, our results show that supportive interaction with community dwellers had a positive relationship with mental health (Models 3 in Table 3, 4, 5, 6). The social supports from or to community dwellers were almost the same in the two age groups (Table 2); however, they were only related with better mental health in the pre-old age adults, especially in terms of ESS. This suggests that promoting community-level interaction from the pre-old stage is important. Cornwell [38] reported weak ties, like contacts with acquaintances or neighbors help with keeping independence for the older people and Stahl et al. [39] reported the beneficial effect of neighborhood social quality on depression for elderly people living alone. Given that family or relatives are connected by marriage or blood and individual friends need time to build and maintain, community dwellers as public resources are available to each community dweller. Our result suggests a feasible low-cost public health intervention by promoting community participation.
Although we hadn’t got a clear figure on the effects of social support during the real old age stage, Models 4, 5, and 6 in Table 3 to Table 6 demonstrated a negative pattern of being in long-term care only in the old-age group. The result is supported by some previous studies that indicated that low functional ability or disability was connected with a high incidence rate of depression [40, 41]. In addition, the present research verified the interaction of functional ability and social support and showed that providing family or relatives instrumental social support may mediate the negative relationship between low functional ability and mental health (Figure A1; see Additional file 5). This suggests that an intervention focused on disadvantaged older people groups could be introduced, which values provided social support within the family.
Taken together, our results confirmed the earlier finding [42] about an inward turn to close relationship in terms of social support in later life, as expected for the shrinking social networks documented in earlier findings [43–45]. In contrast, our data of association between mental health and social support suggested a potentially beneficial meaning of supportive interaction with community people. Given the shrinking social networks along with the natural aging process implies fewer interactions with not-so-close relationships like community neighbors or acquaintances, the older people are potentially at risk of losing availabilities of community-based mental-health-friendly support as time goes on. The intervention of community-based support is suggested to be discussed in the future.
Our investigation illustrated beneficial results of being a provider or a receiver of ESS or ISS on mental health, which echo previous studies [18, 46]; but the positive associations were only among pre-old respondents. An available paper revealed a similar outcome of a more significant association on well-being in the younger-old group [47]. A dynamic view of the aging process is suggested here; while the reasons about age-based differences on social support and mental health haven’t been well documented. Our data depicted a positive association of total received ESS in both pre-old and old groups (Table A1; see Additional file 6), while results in respect of objects varied according to two age phases (Table 3). Subdivision of objects could be an inspiration that contributes to clarifying the age-specific mechanism of social support and mental health in the future.
There were some limitations to our research. First, we used a cross-sectional sample which limited our ability to establish a causal relationship. Second, although quota sampling was conducted to compare different ages and subdivisions of social support, it introduced a weakness concerning representation and generalization of results. Third, few items of social support were designed to ease the burden of filling up the questionnaire, considering the physical and comprehension limitations of the older people. More details on the multiple sub-dimensions and need to be investigated in future research.