Included studies
Using electronic database searches we identified 6,556 records for title and abstract screening after removing duplicates (figure 1). We conducted a full text review of 263 records, of which 16 met all the inclusion criteria and were included in the narrative synthesis. Foreign language full text articles were translated (seven in Japanese, two in Spanish, two in German, two in Chinese (simplified) and one in French). No additional studies were found through grey literature searching, or hand searches of journal contents of included studies’ reference lists.
Initial rates of agreement between the two reviewing authors were 97% for screening, 98% for data extraction and 98% for the quality assessment. All disagreements were resolved through discussion.
Study characteristics
The 16 included papers reported results from 15 different studies, with one study reported in two included papers [28, 29] at different follow-up time points.
Of the 15 samples included (Table 1), nine sampled populations in North America (USA and Canada) [28–36], two in China [37, 38] two in Israel [39, 40], one in Colombia [41] and one in Norway [42]. The earliest study was published in 1985 and the most recent in 2019. The sample size of included studies ranged between 44 and 803 participants. Mean age of samples ranged between 33 and 79 and, except for one study, the majority of participants in each sample were female. Participant groups were defined as those bereaved by natural disasters [28, 37, 38, 42, 43], homicide [30–32, 34], suicide [35, 39, 40, 44], accidental death [36, 45] or armed conflict [41]. One study was longitudinal in design (27), and measured outcomes six months after baseline measurement (at a mean of 1.66 years post-loss). Another study (25) followed-up a sample described in an included cross-sectional analysis [28] but reported different measures, so was essentially a separate cross-sectional analysis and not comparable. All other studies were cross-sectional in design.
Across the 15 different studies, 11 different validated measures of social support were used (table 2). The Multidimensional Scale of Perceived Social Support (MSPSS) [46] was the most frequently included measure, employed in five studies [30, 32, 37, 39, 40].
Measures were based on different theoretical approaches to social support, with some distinguishing between perceived and received social support (measuring one or both), and some distinguishing between structural support (integration with social network) and functional support (specific functions provided by others) and measuring one or both [47], and some developed and validated for specific populations.
Across the 15 different studies, 15 different mental health and psychological wellbeing outcomes were measured. The most frequently measured outcomes were post-traumatic stress disorder [31, 32, 34, 36, 38, 41], depression [28, 31, 32, 34, 35, 44, 45] and complicated grief [31, 32, 34, 40, 42]. The remaining measures were of other distinct psychiatric and psychological wellbeing outcomes (table 3). No studies measured service use as an indicator of wellbeing. Where studies measured prevalence of an outcome rather than symptom severity, a cut-off score on an assessment tool was used rather than self-report of an existing clinical diagnosis.
Quality assessments
Table 4 shows the results of the NOS quality assessments for included studies. Most studies were judged as either good quality [34, 36, 38, 40, 42, 44] or fair quality [28, 29, 31, 41, 45], and five studies were rated as poor quality [30, 32, 35, 37, 39].The most frequent source of bias was sample size. No studies were deemed to have a justified sample size as none had carried out a power calculation. Low response rate or no response rate, and lack of comparison between respondents and non-respondents were also a common source of bias across studies, where 13 studies did not meet the criteria to score a point in this category.
In addition to the NOS, we noted that exploratory approaches were common, with multiple statistical models often used in study analyses, reflecting multiple outcomes and exposure variables. There was also great variation in the degree to which analyses controlled for potential confounding variables, and in the specific variables chosen as potential confounders, resulting in a risk of residual confounding in reported estimates.
Summary of findings
Table 5 summarises the overall findings extracted from included studies for each outcome type.
Psychiatric Outcomes
Depression (seven studies)
There was limited evidence that social support was associated with reduced risk of meeting the threshold for depression diagnosis or reduced depression symptom severity, with seven studies [28, 31, 32, 34, 35, 44, 45] measuring this outcome. The single longitudinal study [31] included in this review was of fair quality and was exploratory in nature, but did control for baseline outcome measures. This study found no association between the two variables.
Four studies [28, 34, 35, 44] reported a positive association between measures of social support and depression; two were good quality [34, 44], one was fair quality [28] and one was poor quality [35].
Two more exploratory studies reported a partial positive association between social support and depression. A study judged as fair quality [45] found that only one (perceived support from friends) of two social support variables in one of three analysis models was cross-sectionally associated with reduced symptom severity, with the other 2 models finding no association. A poor quality study [32] found that two (grief support and percentage of anticipated negative relationships) of six social support variables correlated significantly with reduced symptom severity.
PTSD (six studies)
There was limited evidence that social support was associated with a reduced risk of meeting the threshold for PTSD diagnosis or with reduced symptom severity. All six studies [31, 32, 34, 36, 38, 41] that measured PTSD as an outcome found some evidence of an association between increased social support and reduced severity of/likelihood of meeting threshold for PTSD, however studies were of mixed quality.
In the longitudinal study [31], one (satisfaction with physical assistance) out of twelve measured social support variables predicted lower symptom severity. Another poor quality study [32] found a partial positive association, with only one (percentage of actual negative relationships) of out six social support variables correlated with lower symptom severity.
Four other studies [34, 36, 38, 41] found a positive association between social support and PTSD. Three of these studies were of good quality [34, 36, 38] and one was of fair quality [41].
Complicated grief [CG] (six studies)
There was mixed evidence regarding whether social support was associated with a reduced risk of meeting the threshold for CG diagnosis or reduced symptom severity, with six studies [31, 32, 34, 37, 40, 42] measuring this outcome. The included longitudinal study [31] found that only one (satisfaction with physical assistance) of twelve social support variables was associated with CG, predicting increased severity of symptoms.
Two studies reported a positive association: two good quality studies [40, 42] reported a positive association between the social support risk of CG. Another study [32] found a partial positive association; this poor quality study found that two (percentage of actual negative relationships and available support system) of six social support variables was correlated with reduced symptom severity of CG.
Two more studies [34, 37], one poor quality [37] and one good quality [34], found no cross-sectional association between social support and CG.
In one fair quality cross-sectional study [41]assessed the outcome of prolonged grief, a concept similar to CG, and found no association with social support.
Other psychiatric outcomes (two studies)
The outcome of anxiety was measured in the included longitudinal study [31], where one of twelve measured social support variables at T1 significantly predicted lower levels of anxiety at T2 and the other variables showing no association.
A separate good quality study [44] found a significant positive association between a global social support measure and lower levels of suicidal ideation.
Other psychological wellbeing outcomes (eight studies)
Nine separate psychological wellbeing outcomes were measured, demonstrating limited evidence that social support is associated with improved psychological wellbeing.
There was consistent evidence that social support influences positive wellbeing, with three separate studies [30, 39, 44] measuring personal growth, stress-related growth and resilience. A good quality study [44] found that increased personal growth was cross-sectionally associated with increased social support, and a low quality study [39] found that increased stress-related growth was cross-sectionally associated with increased social support. Social support mediated the association between traumatic stress and resilience in a poor quality study [30].
The similar constructs of grief, mourning, and extent of grief difficulties, were each significantly cross-sectionally associated with social support in two separate exploratory studies [36, 44], both high quality.
Two studies measured distress with conflicting findings; one fair quality study [41]found a positive association between social support and emotional distress whereas another fair quality study [29]found no cross-sectional association between social support and mental distress.
A single fair quality study [45] assessed the initial impact of event (IES) and found that one (perceived support from friends) of two social support variables in one of three analysis models was cross-sectionally associated with reduced impact, the other two models finding no association.
Two further psychological outcomes, loneliness [35] and recovery [29], were mentioned as having been measured in the methods sections of separate studies but were not included in statistical analysis models reported.
Subgroup: people bereaved by suicide (four studies)
Four of the cross-sectional studies reported above [35, 39, 40, 44] included only participants who had been bereaved by suicide, each controlling for a range of demographic and health-related variables. Study results consistently found that increased social support was associated with improved wellbeing.
One poor quality study [39] found a partial positive association between social support and stress-related growth, and another good quality study [40] found that social support was cross-sectionally associated with a significantly reduced risk of CG.
Two other exploratory cross-sectional studies [35, 44], one good quality [44] and one poor quality [35], demonstrated a positive association between social support and depressive symptoms, suicidal ideation and grief difficulties.
Other subgroups
No other meaningful patterns of results defined by subgroups became apparent during the process of data synthesis, whether based on type of loss or type of social support measurement. Insufficient information was provided in studies to compare results by relationship type or time since loss and the limited number of longitudinal studies did not allow for consideration of whether studies support or refute the main effects or buffering models of social support.