Effectiveness of Social Support for Community-Dwelling Elderly with Depression: A Systematic Review and Meta-Analysis

Depression in the elderly is an important health factor that requires intervention in the form of social support resources. The purpose of this study was to conduct a systematic review, while synthesizing available evidence on what kind of social support, such as social participation and social connection/network, is effective for depression in the elderly. We performed a quality assessment of the included studies using the revised Risk of Bias for Non-randomized Studies tool and a meta-analysis of studies published up to 14 May 2021. Of the 3449 studies, 52 were relevant to this study. The various types of social resource applications reported in these were classified into three types: social support, social participation, and social connection/network. The social support group had significantly lower depression compared to the control group (0.72 [0.65, 0.81], p < 0.00001, I2 = 92%). There was a significant decrease in depression in the social participation group compared to the control group (0.67 [0.56, 0.80], p < 0.00001, I2 = 93%) (2.77 [1.30, 5.91], p = 0.008, I2 = 97%) (0.67 [0.56, 0.80], p < 0.00001, I2 = 93%). Finally, the social connection/network group showed decreased depression compared to the control group (2.40 [1.89, 3.05], p < 0.00001, I2 = 24%) (0.83 [0.76, 0.90], p < 0.00001, I2 = 94%). The results of this systematic review confirmed the effects of various social support interventions in reducing depression among the elderly living in the community.


Introduction
The pathophysiological model of human health and disease has succeeded to some extent in identifying its causes and consequences through continuous research spanning decades. However, studies on the socio-psychological impacts on human health and disease have received relatively less attention [1]. Nevertheless, the social impact on health, especially the effect of social relations, has been reported through recent studies [2,3]. More specifically, the influence of social relationships is related to the number of human relations and their quality and effects in terms of social connections [1,4]. We need to pay attention to this social connection, especially in the case of the elderly, as it can be seen that the quantity and quality of social connections directly affect the health of the elderly [1,5,6]. For example, social isolation or loneliness in the elderly was found to be associated with a 50% increased risk of developing dementia [7], 30% increased risk of coronary artery disease or stroke [8], and 26% increase in mortality rates [9]. Although there are differences by country, 16.4% of the elderly living with their spouses and 21.7% of the elderly living with their adult children experienced depression, while 30.2% of the elderly living alone experienced depression [10]. Nurses, as health care professionals, need to identify the effects of social connections on diseases among the elderly and pay attention to depression in the elderly. In particular, among the suicide risk factors in the elderly, depression is an important factor that can be mediated and has been the subject of several suicide prevention studies [11]. However, late-life depression is not easy to agreed upon by the two reviewers.

Statistical Analysis
We conducted a meta-analysis using the Review Manager 5.4 (RevMan) progr for the items that could be synthesized among the results of 52 included studies. The timated effect, measured as odds ratio (OR) with 95% confidence intervals, was extra ed. Between the studies, I 2 statistics were used to evaluate statistical heterogeneity, an fixed-effects model was used to analyze the data. We used a random effects model wh heterogeneity was absent.

Study Selection
After full-test reviews, 3449 studies were searched from the database. After exclu ing duplicates, 2948 studies remained. A full-text review revealed that 52 docume were relevant to this study. Figure 1 illustrates a flowchart of the study selection proce Reliability was checked by two reviewers using Cohen's kappa coefficient (k = 0.85).  Table 1 represents the characteristics of the 52 included studies. The search was c ried out on 14 May 2021. Studies published between 1997, when the search engine sta ed, and 2021 were considered. The selected studies included 42 cross-sectional and longitudinal studies. There were 37 studies from Asia, 11 from North America, two fro Africa, one from Australia, and one from Europe. Specific items for each study were search design, sample size, age, gender of participants, depression and social supp measurement tools, and other related variables. Supplementary Table S1 presents  Table 1 represents the characteristics of the 52 included studies. The search was carried out on 14 May 2021. Studies published between 1997, when the search engine started, and 2021 were considered. The selected studies included 42 cross-sectional and 10 longitudinal studies. There were 37 studies from Asia, 11 from North America, two from Africa, one from Australia, and one from Europe. Specific items for each study were research design, sample size, age, gender of participants, depression and social support measurement tools, and other related variables. Supplementary Table S1 presents the characteristics of the subjects presented in each study, and Supplementary Table S2 presents various depression intervention methods, which are the main interests of this study, classified into social support, social participation, and social connection/network. The scale provides a brief measure of social functioning.

Study Characteristics
(1) how many people are so close to you that you can count on them if you have great personal problems? (none, 1-2, 3-4, and 5 or more),   (1) To consult in trouble (2) To consult in bad physical condition (3) To help with your daily housework (4) To take to a hospital (5) To take care of you

Risk of Bias within Studies
The 15 selected studies were assessed using the revised (RoBANS) tool ( Figure 2). The risk of possibility of target group comparisons and target group selection were low in 35 of the 52 studies. The risk of confounding and selective outcome reporting was low for all studies. The risk of exposure measurement was low in 39 studies. The risk of blinding of assessors was unclear. The risk of outcome assessment was low in 50 studies. The risk of incomplete outcome data was low in 42 studies.

Risk of Bias within Studies
The 15 selected studies were assessed using the revised (RoBANS) tool ( Figure 2). The risk of possibility of target group comparisons and target group selection were low in 35 of the 52 studies. The risk of confounding and selective outcome reporting was low for all studies. The risk of exposure measurement was low in 39 studies. The risk of blinding of assessors was unclear. The risk of outcome assessment was low in 50 studies. The risk of incomplete outcome data was low in 42 studies.

Social Support
The social support group showed significantly decreased depression compared to the control group (0.72 [0.65, 0.81], p < 0.00001, I 2 = 92%) ( Figure 3A). Heterogeneity between studies was confirmed, and an additional subgroup analysis was performed. Subgroup analysis of social support by research type revealed that depression was significantly reduced in longitudinal studies (0.80 [0.72, 0.89], p < 0.0001) as well as in cross-sectional studies (0.71 [063, 0.80], p < 0.00001, I 2 = 93%). Subgroup analysis was performed, but the heterogeneity was not reduced. In the subgroup analysis of social support of articles published by continents, social support significantly decreased depression compared to the control group in the western (0.45 [0.34, 0.61], p < 0.00001, I 2 = 95%) and eastern continents (0.88 [0.83, 0.95], p = 0.0004, I 2 = 54%). The heterogeneity value in eastern countries decreased, and depression decreased as social support increased in both groups.

Social Support
The social support group showed significantly decreased depression compared to the control group (0.72 [0.65, 0.81], p < 0.00001, I² = 92%) ( Figure 3A). Heterogeneity between studies was confirmed, and an additional subgroup analysis was performed. Subgroup analysis of social support by research type revealed that depression was significantly reduced in longitudinal studies (0.80 [0.72, 0.89], p < 0.0001) as well as in crosssectional studies (0.71 [063, 0.80], p < 0.00001, I² = 93%). Subgroup analysis was performed, but the heterogeneity was not reduced. In the subgroup analysis of social support of articles published by continents, social support significantly decreased depression compared to the control group in the western (0. 45

Social Participation
As shown in Figure 3B, high social participation increases depression scores, which means that depression decreases (for tools interpreting depression as decreasing as the number increases). The social participation group reported a significant decline in depression compared with the control group (2.77 [1.30, 5.91], p = 0.008, I 2 = 97%), and all articles in the analyzed group were cross-sectional studies and the published continents were Eastern ( Figure 3B). Figure 3C1 shows that if there is a lot of social participation, the depression score decreases, which means that depression decreases. There was a significant decrease in depression in the social participation group compared to the control group (0.67 [0.56, 0.80], p < 0.00001, I 2 = 93%) ( Figure 3C1). Subgroup analysis was performed to reduce heterogeneity. In the subgroup analysis of social participation by research type, cross-sectional studies did not significantly reduce depression (0.47 [0.18, 1.21], p = 0.12, I 2 = 95%), whereas longitudinal studies did (0.78 [0.72, 0.86], p < 0.00001, I 2 = 82%) ( Figure 3C2). In the subgroup analysis of social participation by published continents, depression in the social participation group was significantly reduced compared to the control group in the western (0.76 [0.59, 0.98], p = 0.03) and eastern continents (0.64 [0.52, 0.79], p < 0.0001, I 2 = 95%) ( Figure 3C3). The effect size of social participation in the eastern (0.64) was larger than that in the western continents (0.76).

Social Connection and Social Network
As shown in Figure 3D1, many social networks increase depression scores. The social network group showed decreased depression compared with the control group (2.40 [1.89, 3.05], p < 0.00001, I 2 = 24%), and all analyzed articles were published in Eastern continents ( Figure 3D1). Subgroup analysis of social networks by published continents revealed that depression was significantly reduced in cross-sectional studies (2.51 [1.91, 3.29], p < 0.00001, I 2 = 34%), but not in longitudinal studies (1.73 [0.84, 3.56], p = 0.14) ( Figure 3D2). Figure 3E1 shows that if there are many social networks, depression scores decrease. There was a significant decrease in depression in the social network group compared to the control group

Discussion
This study is the first to quantitatively synthesize the effect of social support on the elderly in the community using a meta-analysis. We conducted a systematic review of elderly depression in the community and conducted a meta-analysis on what kind of social resources among intervention methods such as social support, social participation, and social network are effective for elderly depression. As a result of the systematic review, which included a total of 52 studies, social support, social participation, and social connection/social network were identified as effective intervention methods for depression in the elderly in the community. In the subgroup analysis of social participation by research type, cross-sectional studies did not significantly reduce depression, whereas longitudinal studies did. Subgroup analysis of social networks by study type revealed that depression significantly decreased in cross-sectional studies but not in longitudinal studies. In the subgroup analysis of social networks by published continents, depression in the social network group was significantly reduced compared to the control group in the eastern, but not in the western continents.

Social Resources Were Effective Interventions for Depression in the Elderly of the Community
Social support, social participation, and social connection/network were identified as effective intervention methods for depression among the elderly in the community. It is necessary to discuss the results of this study and other research using a systematic review. According to a systematic review, which was already conducted 10 years ago, depression decreased in the group that applied social activities compared to the group that did not receive intervention [44]. However, since the number of trials was small, the results should be interpreted carefully. Nevertheless, the study showed that discussion groups sharing experiences with each other, designed to strengthen social networks and support, could help reduce loneliness among the elderly and increase social contact and social activities of the elderly. The 52 studies analyzed in this review also identified studies on interactions with families and neighbors as well as various programs; in this study, they were classified as social participation, including community and individual levels, and the results were found to have a positive effect on depression in the elderly. Another review paper analyzing 21 papers on depression intervention reported a study in which social support intervention had a small but significant effect on the reduction of depression symptoms, reporting that health manager and problem-solving interventions reduced depression [45]. As in the previous study, a systematic review in 2019 strongly supported the results of this study and confirmed the effect of depression intervention on 53 elderly residents in the community. The results of the study indicated that group-centered interventions and interventions including social factors have a positive effect on the mental health of participants. Therefore, group-based interventions should be considered first when considering that many elderly people have social difficulties [46]. Another recent systematic review found that through a total of 66 studies, social support has structural and functional aspects, and perceived social support is more generally measured than received social support. Social support has various factors depending on the study, but it was concluded that there is a clear association between social support and elderly depression [5]. Mohd et al. [5] classified social support into structural aspects such as marital status and residential environment and functional support such as emotional satisfaction. However, this study divided it into social support, social participation, and social connection/network. In conclusion, the results of the systematic review of the effects of depression intervention for the elderly consistently report that studies related to social support or participation are effective in depression.

Implications of the Meta-Analysis and Subgroup Analysis Results
We need to pay attention to the meta-analysis results of this study for the application of social support to practically reduce elderly depression. As mentioned in the results section, in this study, the effects were confirmed through meta-analysis by dividing the interventions for depression of the elderly into three categories: social support, social participation, and social connection/network. The overall meta-analysis results conducted in this study were found to indicate that social support interventions, including social support and social participation, help reduce depression. Additionally, the meta-analysis reported that heterogeneity between the studies was high; therefore, an additional subgroup analysis was performed.
The subgroup analysis of social participation intervention by type of study showed that cross-sectional studies did not significantly reduce depression, while longitudinal studies were found to reduce depression. In other words, long-term follow-up studies confirmed that social participation interventions were effective in depression, thus, they confirmed the positive effect of social participation on depression more clearly. This is because the descriptive cross-sectional study investigates at one point, so it is difficult to generalize the cause and result, while longitudinal research is a study that complements the disadvantages of cross-sectional research. Similarly, as a result of subgroup analysis by research type on social network intervention methods, depression did not decrease in cross-sectional studies, but significantly decreased in longitudinal studies. This difference according to the research type suggests that we should avoid simply understanding the meta-analysis results. In addition, the subgroup analysis of published continental social network interventions showed that depression by social network intervention decreased in Asia compared to the control group, but similar results were not found in the West.
In other words, the results of the subgroup meta-analysis conducted in this study can be presented as follows: First, as suggested in the longitudinal studies, social support, social participation, and social connection/network were all effective interventions for depression among the elderly in the community. Second, interventions using social networks can be more effective in Asian countries than in Western countries. Based on this, the following interventions are needed for nurses to promote social support for the elderly in the community. It is to create a center that can monitor the daily life of the elderly, especially the elderly living alone, centered on the community, and to provide a social support system for the elderly and to create a system that can detect high-risk groups such as depression in advance. It is necessary to make efforts to expand the important role of nurses centering on existing community health centers.

Strengths and Limitations
The main strength of this review is that it is the most recent and comprehensive quantitative synthesis of interventions in terms of social support for depression in the elderly. In particular, this study differs from previous studies in that a review of more effective intervention methods was conducted through meta-analysis by dividing various social supports. In other words, it can be said that the main achievement of this study was to provide practical guidelines for depression interventions for the elderly in the community.
Regarding the limitations of this study, the heterogeneity was high in the studies included in the meta-analysis. However, social support and social participation consistently produce results in the same direction, and it is judged that there will be no difficulty in drawing conclusions. Second, long-term follow-up studies on depression in the elderly are needed, therefore, the current results should be interpreted carefully. Finally, another limitation is that only studies published in English or Korean were used as targets for analysis.

Conclusions
The results of this systematic review support the effects of various social support interventions in reducing depression in the elderly living in the community. Various interventions in the reviewed study were divided into social support, social participation, and social connection/network, and a meta-analysis was conducted. According to the meta-analysis, social support was effective in reducing depression among the elderly in the community; therefore, nurses should allow the elderly in the community to create a system that allows them to perceive social support resources and escape negative emotions such as depression by experiencing emotional support and exchange through social participation. However, not all social resources for depression among the elderly in the community can be provided by nurses; hence, it is necessary to speak out so that related social systems can be established.

Supplementary Materials:
The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/healthcare10091598/s1, Table S1: Characteristics of the subjects presented in each study; Table S2: Various depression intervention methods.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.

Conflicts of Interest:
The authors declare no conflict of interest.