Childhood bullying has a negative impact on mental health, but the effect may be partially attributable to preexisting vulnerabilities and appears to dissipate over time, new research suggests.
A twin study conducted by British researchers showed that being bullied at age 11 years was tied to concurrent mental health problems such as anxiety, depression, hyperactivity, impulsivity, and inattention, as well as conduct problems. Many of these symptoms persisted for 2 years.
However, most problems dissipated or were greatly reduced over time, so that by 5 years, only paranoid thoughts and cognitive disorganization persisted. Additionally, many of the children who were bullied had preexisting vulnerabilities that may have made them more likely to be targets for bullying.
“It is known that bullying does not take place at random, and bullies choose their targets based on a number of risk factors,” lead researcher Jean-Baptiste Pingault, PhD, lecturer, Division of Psychology and Language Sciences, University College London, United Kingdom, told Medscape Medical News.
“Intervening in bullying per se is important but will not solve the problem. It is better to also intervene in specific groups of children that are vulnerable to bullying to address any underlying risk factors and to build resilience,” he added.
The study was published online October 4 in JAMA Psychiatry.
Correlation vs Causation
Previous research has shown that bullying is “associated with a wide range of long-lasting adverse outcomes, particularly mental health outcomes such as anxiety,” the authors write.
However, prior studies, whether cross-sectional or longitudinal, are correlational and therefore “fall short of being able to infer causality,” they add.
Moreover, these studies are not “genetically informative and do not account for genetic confounding,” which is particularly problematic because “genetic influences account for up to two-thirds of the variation in exposure to bullying, suggesting that being bullied is influenced by preexisting heritable individual vulnerabilities.”
These vulnerabilities can independently predispose children to develop mental health problems later in life.
The “person-environment correlations between individual vulnerabilities and exposure to bullying ― or gene-environment correlation when driven by genetic factors ― can generate associations that do not entirely reflect a causal contribution of childhood exposure to bullying.”
To identify potential genetic and environmental confounders, the researchers utilized the “powerful method” of a co-twin design, by which the study included both dizygotic (DZ) and monozygotic (MZ) twins. Through this design, one twin was used as a control for the other.
Although some previous studies also utilized a twin design, the researchers note limitations in those studies, including small sample sizes and lack of long-term outcomes.
“Our motive in conducting this study was that although there is a lot of literature on bullying and mental health, most has a normal correlational design. We wanted to use a more stringent design that is more specific,” Dr Pingault said.
Waning Effect
To investigate the impact of bullying, the researchers drew participants from the Twins Early Development Study (TEDS) who were born in England and Wales from 1994 through 1996. The twins (n = 11,108 including 5894 girls and 5214 boys) ranged in age from 11 years to 16 years between 2005 and 2013, when data were collected.
Childhood bullying was assessed at ages 11 and 14 via the self-report version of the Multidimensional Peer-Victimization scale, a 16-item measure comprising four subscales: physical bullying, verbal bullying, social manipulation, and property attacks.
Outcomes included total mental health difficulties; anxiety; depression; hyperactivity and impulsivity; inattention; conduct problems; and psychoticlike experiences, including paranoid thoughts, hallucinations, grandiosity, cognitive disorganization, anhedonia, and negative symptoms.
Three sets of longitudinal analyses were conducted: concurrent (at age 11 years), 2 years after exposure to bullying, and 5 years after exposure to bullying.
Participants whose exposure was assessed at age 14 years and outcomes at age 16 years were used for the 2-year analysis; for the 5-year analysis, exposure was measured at age 11 years and outcomes at age 16 years.
Several additional scales were used to measure outcomes. Total difficulties, anxiety, inattention, hyperactivity and impulsivity, and conduct problems were assessed using subscales of the Strengths and Difficulties Questionnaire (SDQ). Anxiety was also measured by the Childhood Anxiety Sensitivity Index (CASI) and the Anxiety-Related Behaviors Questionnaire (ARBQ).
Depression was additionally measured by the Moods and Feelings Questionnaire (MFQ), and inattention, hyperactivity, and impulsivity were assessed with the Conners scales. The Specific Psychotic Experiences Questionnaire was used to measure psychoticlike experiences. Both parents and children completed the assessments.
The researchers utilized three main types of estimates of the relationship between exposure and outcome: unadjusted phenotypic estimate, estimate from twin differences in DZ same-sex twins, and estimate from twin differences in MZ twins. Positive regression estimates signified that the twin who was more exposed to bullying also presented with higher levels of mental health difficulties.
The concurrent contributions of past-year exposure to bullying at age 11 to mental health outcomes at age 11, based on the SDQ-Parent (n = 5525, 1799 dizygotic twins of both sexes [DZSS] and 2010 MZ twins), showed a regression estimate of 0.233 for phenotypic (β95% CI, 0.213 – 0.253), 0.181 for DZ differences (β95% CI, 0.130 – 0.232), and 0.043 for MZ differences (β95% CI, 0.010 – 0.075).
A similar pattern was found in the SDQ-Child (n = 5522, 1799 DZSS, 2012 MZ), with a regression estimate of 0.401 for phenotypic (0.382 – 0.420), 0.348 for DZ differences, (0.294 – 0.402), and 0.241 for MZ differences (0.189 – 0.294).
However, at 16 years of age (5-year effect), based on the SDQ-Child (n = 3807, 1241 DZSS, 1403 MZ), the regression estimate was 0.178 for phenotypic (0.154 – 0.203), 0.143 for DZ differences, (0.082 – 0.205), and 0.055 for MZ differences (-0.004 to 0.114).
All DZ differences were based only on same-sex pairs.
Results of the 2-year effect, based on the SDQ-Child (n = 2353, 759 DZSS, 929 MZ), showed an estimate of 0.238 (0.205 – 0.271) for phenotypic, 0.238 for DZ differences (0.154 – 0.327), and 0.106 (0.021 – 0.187) for MZ differences.
Address Vulnerabilities
The researchers note that most of the relationships in the concurrent estimates remained significant when controlling for all shared environmental influences and half of the genetic influences in the DZ analysis.
MZ estimates in the concurrent analysis were “consistent with a causal influence of childhood exposure to bullying” on the total difficulty, depression, and anxiety scores across all informants.
MZ estimates were also significant for child-rated conduct, hyperactivity, and inattention symptoms, based on the SDQ; and parent-related inattention, based on the Conners scales. The findings remained similar when further controlling for prior within-twin differences.
In the 2-year analysis, all phenotypic estimates remained significant, and effect sizes tended to fall between the concurrent and 5-year estimates. In MZ analyses, the total difficulty score, child-rated and parent-rated anxiety on three different scales, as well as paranoid thoughts, hallucinations, and cognitive disorganization were significant.
All phenotypic estimates remained significant for the 5-year analysis, although those estimates were smaller than concurrent and 2-year estimates. However, in the MZ analyses, only paranoid thoughts, cognitive disorganization, and the Conners scale total and inattention scores were still significant.
The researchers explain that the decrease in effect sizes from phenotypic to DZ and MZ estimates suggests “the importance of shared environmental and/or genetic confounding in explaining observed associations between exposure to bullying and multiple mental health problems, especially depression and anxiety.”
Despite this decrease, MZ estimates remained significant for both the concurrent and the 2-year analyses, “supporting an association between childhood exposure to bullying and total difficulties.”
Findings of the 5-year analysis, on the other hand, showed only a “small but enduring contribution” of childhood exposure to paranoid thoughts and cognitive disorganization.
“Overall, this pattern of findings suggests that reported associations between childhood exposure to bullying and mental health outcomes likely reflect, at least in part, multiple vulnerabilities of bullied individuals rather than a causal contribution of childhood exposure to bullying,” the authors write.
“Recognizing that the effects of bullying can be partially attributed to preexisting vulnerabilities such as mental health conditions does not justify bullying, of course,” Dr Pingault added.
“If a child has problems with autistic behavior, for example, or is obese or depressed, the solution is not only to tackle the bullying itself but to empower the children with tools that are as adaptive as possible to their situations,” he added.
The study suggests that the impact of bullying on mental health weakens over time, but in children who were already depressed or had other difficulties, “addressing the depression will have an even longer-term beneficial impact on mental health,” he said.
Contradictory Findings
Commenting on the study for Medscape Medical News, Judy Silberg, PhD, associate professor, Department of Human and Molecular Genetics, Virginia Commonwealth University, Richmond, said the study “recognizes the importance of ‘multiple vulnerabilities’ in children who are bullied and that, in addition to the causal effect of the bullying, interventions should focus on these vulnerabilities in children that are most at risk.”
However, she raised concerns about the study’s implications.
“I would challenge the authors’ assertion that symptoms are markedly reduced by age 16, which contradicts the findings from numerous population-based studies across the world that show a consistent deleterious effect of childhood bullying that can extend into adulthood.”
Many of these studies point to “significantly high rates of depression, anxiety, and even suicidal behavior, so parents should not stop worrying about children just yet,” said Dr Silberg, who is the co-uthor of an accompanying editorial.
However, the current study has important practical implications, she emphasized.
“Bullying should be stopped. The findings of this study also underscore the importance of behavioral interventions that reduce children’s risk of being bullied.”
Dr Pingault agreed that this is the take-home message of the study.
“In addition to trying to stop the child’s exposure to bullying, more attention should be shifted to trying to look at other ways of helping this child by enhancing resilience and addressing relevant preexisting risk factors.”
The Twins Early Development Study is supported by the UK Medical Research Council. This research was funded by the Economic and Social Research Council and MQ:Transforming Mental Health. The authors have disclosed no relevant financial relationships.
JAMA Psychiatry. Published online October 4, 2017. Abstract, Editorial
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