Childhood maltreatment (CM) is a global issue with serious life-long consequences (Fang et al., Reference Fang, Fry, Brown, Mercy, Dunne, Butchart, Corso, Maynzyuk, Dzhygyr, Chen, McCoy and Swales2015; Ferrara et al., Reference Ferrara, Corsello, Basile, Nigri, Campanozzi, Ehrich and Pettoello-Mantovani2015; Gilbert et al., Reference Gilbert, Widom, Browne, Fergusson, Webb and Janson2009). Up to one billion children aged 2–17 years had experienced various types of CM, including physical, sexual, or emotional abuse or neglect (Hillis et al., Reference Hillis, Mercy, Amobi and Kress2016). CM substantially increases the likelihood of later-on mental health problems, for instance, it can increase the risk of depression by 2–3-fold (Chapman et al., Reference Chapman, Whitfield, Felitti, Dube, Edwards and Anda2004; Li et al., Reference Li, D'Arcy and Meng2016).

Social support and coping strategies are the most frequently studied factors that are involved in the relation between CM and mental health outcomes (Runtz & Schallow, Reference Runtz and Schallow1997; Vranceanu et al., Reference Vranceanu, Hobfoll and Johnson2007; Zhao et al., Reference Zhao, Peng, Chao and Xiang2019). Social support refers to an individual’s perception of being loved, cared for, respected, and valued by other members of the community (Cobb, Reference Cobb1976). Coping strategies refer to psychological patterns that individuals use to manage thoughts, feelings, and actions (Franklin, Reference Franklin, Morris and Knechtle2014; Lazarus & Folkman, Reference Lazarus and Folkman1984) and are generally categorised into positive and negative coping (or adaptive and maladaptive coping) based on the outcomes that have been associated with these behaviors (Smedema & McKenzie, Reference Smedema and McKenzie2010). The associations between social support, coping strategies, and mental health outcomes are often made under the context of a stress coping framework (Chernomas, Reference Chernomas2014). Reviews have consistently synthesized that both social support and positive coping strategies are associated with positive health outcomes in maltreated victims (Domhardt et al., Reference Domhardt, Münzer, Fegert and Goldbeck2015; Dufour et al., Reference Dufour, Nadeau and Bertrand2000; Meng et al., Reference Meng, Fleury, Xiang, Li and D’Arcy2018; Su et al., Reference Su, Meng and D'Arcy2020), whereas negative coping strategies are associated with more severe psychiatric problems, depressive symptoms, and life dissatisfaction (Gustems-Carnicer & Calderón, Reference Gustems-Carnicer and Calderón2013; Hebert et al., Reference Hebert, Zdaniuk, Schulz and Scheier2009).

Studies have been conducted to explore the potential mechanisms of social support and coping strategies in the relation between CM and depression. Many cross-sectional studies have tested both moderating (Dale et al., Reference Dale, Weber, Cohen, Kelso, Cruise and Brody2015; Easton et al., Reference Easton, Kong, Gregas, Shen and Shafer2017; Eisman et al., Reference Eisman, Stoddard, Heinze, Caldwell and Zimmerman2015) as well as mediating (Arslan, Reference Arslan2017; Lagdon et al., Reference Lagdon, Ross, Robinson, Contractor, Charak and Armour2021; Massing-Schaffer et al., Reference Massing-Schaffer, Liu, Kraines, Choi and Alloy2015; White Hughto et al., Reference White Hughto, Pachankis, Willie and Reisner2017) effects in the relation between CM and depression. The correlations between perceived social support and coping strategies have also been well-documented (Çevik & Yildiz, Reference Çevik and Yildiz2017; Fiksenbaum et al., Reference Fiksenbaum, Greenglass and Eaton2006; Holahan, Valentiner, et al., Reference Holahan, Valentiner and Moos1995; Roohafza et al., Reference Roohafza, Afshar, Keshteli, Mohammadi, Feizi, Taslimi and Adibi2014). Previous literature suggests that social support and coping strategies could act in a sequential manner to mediate different health outcomes. For instance, high social support predicted less subsequent depression in cardiac illness patients, and this relation was partially mediated by adaptive coping strategies (Holahan, Moos, et al., Reference Holahan, Moos, Holahan and Brennan1995). A more recent study discovered mediating effects of positive and negative coping strategies in the relation between social support and anxiety symptoms in Chinese medical staff during the COVID-19 pandemic (Zhu et al., Reference Zhu, Wei, Meng and Li2020). Studies also suggested that social support may also mediate the relation between coping strategies and mental health outcomes. The mediating roles of three sources of social support (subjective support, family support, and counselor support) were found between cognitive coping and behavioral coping, and anxiety, respectively (Li & Peng, Reference Li and Peng2021). This finding could be partially explained by the fact that social support could serve as coping assistance (Thoits, Reference Thoits1986), and it could work with positive coping strategies to eliminate or alter problematic demands and control the feelings of anxiety or depression that are usually triggered by those demands.

Radell et al. (Reference Radell, Abo Hamza, Daghustani, Perveen and Moustafa2021) suggested that different types of CM may have different etiological contributions relating to depression. For example, psychological abuse was often found to be strongly associated with depression later in life (Infurna et al., Reference Infurna, Reichl, Parzer, Schimmenti, Bifulco and Kaess2016; Powers et al., Reference Powers, Ressler and Bradley2009; Shapero et al., Reference Shapero, Black, Liu, Klugman, Bender, Abramson and Alloy2014; Spertus et al., Reference Spertus, Yehuda, Wong, Halligan and Seremetis2003) and depression severity (Nelson et al., Reference Nelson, Klumparendt, Doebler and Ehring2017), whereas neglect was a stronger predictor of adult depression compared to physical and sexual abuse in childhood (Powers et al., Reference Powers, Ressler and Bradley2009). The mediating effects of social support and coping strategies had also been separately examined in the relations between specific types of CM and depression (Berg et al., Reference Berg, Hobkirk, Joska and Meade2017; Zhang et al., Reference Zhang, Li, Wang, Li, Long and Cao2020; Zhou et al., Reference Zhou, Feng, Hu, Pao, Xiao and Wang2019). However, there is a lack of research conducted to compare the mediating effects of social support and coping strategies in the relations between various types of CM and depression.

Depression is moderately inheritable (probably 40%∼50%) (Levinson & Nichols, Reference Levinson and Nichols2022) and ample studies have recognized the joint contributing roles of genetic predispositions and CM in depression (Grabe et al., Reference Grabe, Schwahn, Appel, Mahler, Schulz, Spitzer, Fenske, Barnow, Lucht, Freyberger, John, Teumer, Wallaschofski, Nauck and Völzke2010; Li, Liu et al., Reference Li, Liu, D'Arcy, Gao and Meng2020; Normann & Buttenschøn, Reference Normann and Buttenschøn2020). It is well accepted that CM interacts with genetic vulnerability to produce lasting effects on the neural structure or function and stress physiology (McEwen et al., Reference McEwen, Gray and Nasca2015) and increases the risk of mental disorders (McEwen, Reference McEwen2007). For example, the polymorphisms of 5-HTTLPR which are involved in the regulation of serotonergic signaling and emotional behaviors and play an important role in brain development and function were found to interact with CM in determining the risk of adult depression (Brown et al., Reference Brown, Ban, Craig, Harris, Herbert and Uher2013; Caspi et al., Reference Caspi, Sugden, Moffitt, Taylor, Craig, Harrington, McClay, Mill, Martin, Braithwaite and Poulton2003). Studies have also been conducted to investigate the genetic basis of stress coping which in turn related to the development of depression (Horwitz et al., Reference Horwitz, Czyz, Berona and King2018; Skapinakis et al., Reference Skapinakis, Bellos, Oikonomou, Dimitriadis, Gkikas, Perdikari and Mavreas2020). Met allele carriers of brain-derived neurotrophic factor reported higher levels of emotion-focused coping strategies compared to Val/Val individuals (Caldwell et al., Reference Caldwell, McInnis, McQuaid, Liu, Stead, Anisman and Hayley2013). A systematic review of genetic influences on stress coping strategies also discovered differential coping strategies among people with different genotypes of the serotonin transporter (SLC64A) and the adrenergic receptor beta 2 (ADRB2) (Dunn & Conley, Reference Dunn and Conley2015). Because of the role of genetic predispositions in stress coping and to control its potential confounding in the relation between CM and depression, it is crucial to control for genetic predispositions while examining the roles of social support and coping strategies in the relation between CM and subsequent depression.

The literature highlights the importance of social support and coping strategies in the relation to CM and depression and has valuable attempts to identify their specific roles in this relation. An in-depth exploration of the sequential order of social support and coping strategies is needed to triangulate their roles in the relation between CM and depression. There are several limitations in the literature: (a) previous mediation studies were mainly cross-sectional without temporal order among studied variables (Lagdon et al., Reference Lagdon, Ross, Robinson, Contractor, Charak and Armour2021; Li & Peng, Reference Li and Peng2021; Zhu et al., Reference Zhu, Wei, Meng and Li2020). There is a lack of causal evidence on the mediating effects of social support and coping strategies in the relation between CM and depression. (b) Little is known about the sequential chains among social support and coping strategies as mediators in this relation. (c) A better understanding of how social support and coping strategies mediate the relations between different types of CM and major depressive disorder (MDD) can help to elucidate the differential effects of various stressors in MDD. (d) Other meaningful factors, such as sociodemographic characteristics and genetic predispositions, have not been comprehensively studied in previous mediation studies either.

To address the knowledge gap in the potential mediating effects of social support and coping strategies, the present study aimed to articulate their roles in the relation between CM and subsequent depression with a comprehensive exploration of other potential factors in a longitudinal cohort study. We hypothesized that social support and coping strategies not only simultaneously but also sequentially mediate the relation between CM and depression. Figure 1 presents the conceptual framework of the present study. This study also tested all the possible serial chains among social support and coping strategies to explore their potential mechanisms in the relation between CM and depression, which can (a) help to explain why maltreated individuals are more likely to develop depression in adulthood on average, and (b) direct intervention and prevention strategies and efforts for maximum payoff. We also compared the mediating effects of social support and coping strategies in the relations between different types of CM and depression and considered the genetic predispositions of depression and sociodemographic characteristics (age, sex, ethnicity, and education) that might also contribute to the different likelihood of depression onset.

Figure 1. The conceptual framework of the present study.

Results

Of the 902 participants, most were females (n = 586, 65.0%), had post-secondary degree or diploma (n = 624, 69.2%), being French-Caucasian (n = 430, 47.7%) or non-Caucasian (n = 381, 42.2%), and were not diagnosed with MDD at Wave IV (n = 676, 74.9%). Table 1 presents a summary of the study cohort stratified by MDD. Participants were more likely to be diagnosed with MDD if they were: not graduating from secondary schools, or French-Caucasian. MDD was positively associated with CM and its subtypes and negative coping but negatively associated with social support and positive coping. No significantly statistical differences were found in age, sex, and PRS_MDD between participants with and without MDD.

Table 1. Characteristics of the study cohort stratified by depression status (N = 902)

Note.

^a χ ² tests.

^b t-tests.

^c Logistic regressions adjusted for principal component scores (pc1 to pc10). PRS, polygenic risk score.

Table 2 presents correlation tests among CM, social support, positive and negative coping strategies, age, and PRS_MDD. CM was positively associated with negative coping and inversely associated with both social support and positive coping. As expected, social support was positively associated with positive coping, whereas negatively associated with negative coping. Positive coping was negatively associated with negative coping. These results satisfied our criteria for testing potential mediation among these variables. In addition, age was positively correlated with CM and negatively correlated with social support. PRS_MDD was positively associated with CM.

Table 2. Pearson correlations among childhood maltreatment, social support, positive and negative coping strategies, age, and PRS_MDD

Note. *p < 0.05; **p < 0.01.

Mediation effects of social support, positive and negative coping strategies

Both parallel and serial mediation analyses were used to explore the potential mediating mechanisms of the studied variables. A series of parallel mediation path analysis models were used to examine the DEs of CM (Figure 2), as well as its subtypes (Appendix 3), on subsequent MDD as well as any IEs potentially mediated by social support, positive and negative coping strategies. Table 3 presents the DEs, total indirect effects, IEs of each mediator, and ratios of IEs to the total effect. We present the results by different types of maltreatment.

Figure 2. Parallel Mediation Model (PMM). Indirect effects of childhood maltreatment on major depressive disorder (MDD) through social support, positive coping, and negative coping, respectively. Models were controlled for age, sex, education, ethnicity, and PRS. Unstandardized effects are presented. *p < 0.05, **p < 0.01, ***p < 0.001.

Table 3. Direct and indirect effects and ratio of indirect to total effects for parallel mediation models (PMMs)

Notes. Table shows unstandardized direct effects and indirect effects with bootstrapped 95% confidence intervals. X, exposure. M, mediator. Mediators in bold indicate statistically significant indirect effects. LLCI, lower limit confidence interval; ULCI, upper limit confidence interval; CM, childhood maltreatment; MDD, major depressive disorder; EA, emotional abuse; PA, physical abuse; SA, sexual abuse; PN, physical neglect; EN, emotional neglect.

^a Ratio of indirect effect to total effect = indirect effect β/(direct effect β + total indirect effect β).

*p < .05; **p < .01.

Any CM and MDD

CM was directly and significantly associated with subsequent MDD (DE = 0.015, SE = 0.007, p = 0.027). Significant IEs of social support (IE = 0.004, Boot SE = 0.002, Boot 95% CI = 0.0001–0.008) and negative coping (IE = 0.013, Boot SE = 0.003, Boot 95% CI = 0.008–0.020) on the association between CM and MDD were also noted. Their mediation effects accounted for 12.1% for social support, and 39.4% for negative coping, of the total effect on the association between CM and MDD. The ratio of the total IE to the total effect was 54.5%. No significant mediation effect of positive coping was found.

Subtypes of maltreatment and MDD

We also conducted subgroup analyses classified by different subtypes of CM. Significant DEs were found for the associations between emotional neglect (DE = 0.042, SE = 0.021, p = 0.042) and physical neglect (DE = 0.081, SE = 0.035, p = 0.021), respectively, and MDD. Negative coping strategies mediated the associations between all different types of maltreatment and MDD, with the mediation effects accounted for 31.0%–44.3% of total effects. Social support only mediated the associations between emotional abuse and physical abuse, respectively, and MDD, with the mediation effects accounted for 11.3% for emotional abuse and 15.6% for physical abuse.

Serial causal effects of social support, positive and negative coping

SMMs were performed to examine whether these mediators (social support, positive and negative coping strategies) sequentially mediating the impact of CM on MDD. Figure 3 illustrates an example of the six SMMs and coefficients of each path (CM→social support→positive coping→negative coping). The rest of the SMMs and coefficients are shown in Appendix 4. Table 4 presents the IEs of each path in these serial models and their ratios to the total effects of CM on MDD. These three mediators in all the six possible serial orders partially mediated the relation between CM and MDD (total IE = 0.018, Boot SE = 0.004, Boot 95% CI = 0.012–0.026). The DE of CM on MDD was 0.015 (SE = 0.007, p = 0.027, 95% CI = 0.002–0.028), and the ratio of the total IE to the total effect was 0.545. The DE, total IE, and the ratio to the total effect, were the same as in the PMM for CM group.

Figure 3. Serial Mediation Model (SMM). Indirect effects of childhood maltreatment on major depressive disorder (MDD) through serial chains of social support, positive coping, and negative coping. The model were controlled for age, sex, education, ethnicity, and PRS. Unstandardized effects are presented. *p < 0.05, **p < 0.01, ***p < 0.001.

Table 4. Indirect effects and ratio of indirect to total effects for the paths on the serial mediation models (SMMs)

Notes. Table shows unstandardized direct effects and indirect effects with bootstrapped 95% confidence intervals. Paths in bold indicate statistically significant indirect effects. LLCI, lower limit confidence interval; ULCI, upper limit confidence interval; CM, childhood maltreatment; MDD, major depressive disorder; SS, social support; PC, positive coping; NC, negative coping.

^a Ratio of indirect effect to total effect = indirect effect β/(direct effect β (0.015) + total indirect effect β (0.018)).

When considering three mediators simultaneously in the relation between CM and MDD, all six models were compared in terms of the significant path created by each different order of the mediators. All the models yielded three to six significant indirect paths out of the seven possible paths. Three of the six models yielded significant indirect paths involving all three mediators in a serial model with the equal ratio of indirect to total effect (0.030) (CM→SS→PC→NC→MDD (SMM1), CM→PC→NC→SS→MDD (SMM3), CM→PC→SS→NC→MDD (SMM4), and CM→NC→PC→SS→MDD (SMM5)). These results showed that exposure to CM led to the poor social support or increased negative coping strategies as well as reduced positive coping strategies, which in turn increased the risk of MDD.

The indirect paths involving positive coping and negative coping/social support (one after the other and vice versa) were statistically significant in two out of the six SMMs, specifically in SMM3 and SMM4.

The indirect paths involving negative coping and social support (one after the other and vice versa) were statistically significant in all SMMs. This indicates that the exposure to CM increased negative coping (or decreased social support) which in turn decreased social support (or increased negative coping) resulting in an elevated risk of subsequent MDD. The serial mediating effects of these two mediators were significant in all the serial models.

Sensitivity analyses

To explore whether MDD status could influence the results, sensitivity analyses were conducted for those without MDD at Wave I. A total of 614 participants were included in the sensitivity analyses. Of which, 59 (9.6%) participants were firstly diagnosed with MDD from Wave II to Wave IV. Both parallel and serial mediation analyses identified the similar results, with negative coping strategies being the significant mediator in the relation between CM and MDD. In the PMM, Significant IEs of negative coping (IE = 0.004, Boot SE = 0.003, Boot 95% CI = 0.003–0.011) was found in the relation between CM and MDD. The total IE was 0.0103 (Boot SE = 0.005, Boot 95% CI = 0.003–0.021). The mediation effect of negative coping accounted for 8.3% (0.0044/(0.042 + 0.0103)) of the total effect. No significant mediation effect of social support or positive coping was found. In the SMMs, the mediators partially mediated the relation between CM and MDD in the path CM→positive coping→social support→negative coping→MDD (IE = 0.0002, Boot SE = 0.0002, Boot 95% CI = 0.00002–0.001). This serial mediation effect accounted for 0.38% (0.0002/(0.042 + 0.0103)) of the total effect.