Contributions of childhood peer victimization and/or maltreatment to young adult anxiety, depression, and suicidality: a cross-sectional study

Our study sample comprised participants of the ongoing, Internet-based Students’ Health Research Enterprise (i-Share) project, a prospective, population-based study of volunteer students in French-speaking universities and higher education institutions. Enrollment in the i-Share project started in 2013; to be eligible, a student had to be officially registered at a University or higher education institute, at least 18 years of age, able to read and understand French, and provide informed consent for participation. The i-Share enrollment procedure was described previously [23].

The self-administered baseline questionnaire collected sociodemographic characteristics, health information, personal and familial histories, living conditions, and consumptions. For this cross-sectional retrospective study, participants completed the baseline questionnaire and a complementary questionnaire, which was proposed after inclusion to the study. Student volunteers received compensation of a 20-euro gift card for completing the supplementary questionnaire, part of which included questions about childhood adversity. For the present study, we retrieved data from a sample of students that were included in the i-Share cohort study between February 2013 and September 2019, had participated in the complementary questionnaire, and had data available on the outcomes of interest.

We first described the overall study sample, and grouped participants according to the categories of the exposure variable (i.e., none, peer victimization only, maltreatment only, or both maltreatment and peer victimization). Continuous variable “age” is expressed as the mean ± standard error. Categorical variables are described as the count and proportion (%). The Kruskal-Wallis test was used to compare distributions of age in the exposure variable groups. Proportions were compared with the Chi-square test.

We evaluated maltreatment and/or peer victimization associations with other binary outcomes (i.e., “anxiety”, “depression”, or “any mental health problems”) by performing binary logistic regression analyses. The results are expressed as adjusted odds ratios (aORs) with 95% confidence intervals (CIs). Because STB was a categorical variable with three modalities, we constructed multinomial logistic regression models to assess relationships between STBs and exposures. Model convergences were checked. The assumption of linearity of the logit was tested for the continuous variable, age, in each model. The fully adjusted analyses took into account all selected covariates. In each model, to account for missing information on covariates, we used the multiple imputation by chained equation method [29]. Briefly, we performed 10 imputations and averaged the variable estimates to produce a mean estimate. Finally, we verified that the relative efficiency of the imputation for each variable was greater than 95%. We also constructed multivariate models to test the interaction between participant sex and the exposure variable for each outcome. Then, to test the cumulative effect of both maltreatment and victimization on mental health outcomes, compared to peer victimization alone and maltreatment alone, we conducted the same analyses, but changed the reference categories.

Finally, the attributable fraction (AF) was defined as the proportion of each mental health outcome that was attributable to peer victimization or parental maltreatment or both, calculated as follows: AF = [p*(aOR-1)] / [1+ (p*(aOR-1)], where p was the prevalence of the risk factor in our study sample, and aOR was the adjusted odds ratio related to the association between the risk factor and the outcome in the multivariate model after the imputation for missing data.

In this cross-sectional study of 2271 young French adults, we found an increased risk of mental health problems, including anxiety, depression, and STBs, in individuals that had been victimized by peers, whether or not they were exposed to parental maltreatment in childhood. Among individuals that were exposed to both maltreatment and peer victimization during childhood, depression and anxiety did not occur significantly more frequently than those exposed to either maltreatment or peer victimization alone. However, the combined exposure significantly increased the risk of suicidal thoughts with suicide attempts, compared to either exposure alone.

The prevalence of peer victimization and maltreatment in our sample were close to those estimated in previous studies [2, 10‐12]. Peer victimization alone was highly prevalent (one third of the sample), which explained the large AFs, comparable to the AFs of the combination of maltreatment and peer victimization.

Our results suggested that peer victimization played an important, independent role in mental health problems, consistent with findings in other studies [30]. A previous longitudinal study highlighted the finding that peer victimization had an independent effect on the mental health of young adults, and the long-term adverse effects on mental health were worse than the effects from maltreatment [31]. Previous studies also showed that peer victimization had an important effect on mental health problems; indeed, the risk of negative mental health outcomes was similar between children that had experienced bullying victimization and children that were placed in institutional or foster care [32].

Studies have shown that parental support and a positive familial relationship in childhood have positive long-term effects on adult mental health and provide a crucial foundation for social interactions [33, 34]. Thus, parental maltreatment in childhood increases the likelihood that a child will be victimized by peers, due to the child’s impaired emotional regulation skills [35]. Indeed, attachment theory highlights the fact children internalize aspects of caregiving relationships, and this experience can later impair peer interactions [36]. It is worth noting that maltreatment and peer victimization refer to experiences of interpersonal violence that occurs in two different environmental contexts – the home and the school, respectively. It is possible that some individuals that experience maltreatment in the home environment see themselves as victims, regardless of the context. However, our results showed that associations between peer victimization and mental health outcomes were not fully explained by exposure to both these types of interpersonal violence. Moreover, these associations remained significant, even after controlling for important familial variables. This finding emphasized the importance of interpersonal experiences that occur outside the family sphere, and specifically with peers, which appear to play a specific role in mental health. As children grow-up, peer interactions become increasingly important. Repetitive verbal or physical harassment or exclusion from peers might have long-term effects, independent of other childhood adversities, and thus, they can modify responses to stress [37]. Furthermore, our findings suggested that cumulative maltreatment effects may be at least partly due to victimization. Thus, future studies of maltreatment should also take into account peer victimization.

In suicide ideation-to-action frameworks, such as the Interpersonal Psychological Theory of Suicide [38], or more recently, the Three-Step Theory [39], the development of suicide ideation and its progression to suicide attempts are distinct processes with different explanations and risk factors. These theories emphasize an ‘acquired capability’, which refers to an individual’s habituation to pain or fear through exposure to life experiences, such as abuse or other painful events. Our findings showed that cumulative exposures to parental maltreatment and peer victimization were more strongly associated with the risk of suicidal ideation and suicide attempts than with the risk of suicide ideation alone. This finding suggested that cumulative experiences could promote progression of the acquired capability from suicide ideation to suicide attempts.

The present study had some important strengths, including the large, contemporaneous sample of young French adults, a study population never investigated on this subject. We also note the consistency of our results with previous studies, and the ability to adjust for a range of confounders, due to the data available on a wide range of variables. Depression and anxiety were measured with validated scales that had excellent psychometric properties. Furthermore, we found a significant association between peer victimization alone and each mental health outcome, which provided consistent results. Despite these strengths, several limitations should be considered when interpreting the results. First, the study design was cross-sectional; therefore, we could not strictly correlate the exposure timing to the outcome and the covariates, and we could not infer causality between the exposure and the mental health outcomes. Second, the voluntary participation of students in the baseline and supplementary questionnaires may have introduced a self-selection bias, although it is difficult to predict how this potential bias could have influenced the results. Third, the information was self-reported, which could lead to an information bias, particularly a memory bias, because the exposure assessment was retrospective. Fourth, there was an over-representation of women in our sample, compared to the 56% of female students in France, and our results suggested that there were differences between the sexes, in terms of mental health problems and maltreatment exposure. Fifth, we did not analyze physical and psychological maltreatments separately, with regard to peer victimization. Finally, we could not investigate the age of onset for peer victimization and/or maltreatment.