A number of recent studies have examined the impact of bullying during childhood and adolescence on the development of mental health issues later in life.

The Avon Longitudinal Study of Parents and Children, an ongoing observational study in the U.K., interviewed over 6,000 adolescents about peer victimization at age 13 (Bowes et al. Br Med J 2015; epublished June 2, 2015). Overall, 101 of 683 participants (14.8%) reporting frequent victimization met ICD-10 criteria for depression at age 18. In comparison, the prevalence of depression at age 18 was 7.1% for those reporting some bullying, and 5.5% for those with no history of being bullied. The odds of depression at age 18 with frequent versus no victimization was 2.32 (adjusted for confounders). The group estimated that 29.2% of depression at age 18 could be attributable to bullying, although it should be noted that an observational study design cannot determine causality.

A prior analysis of the Avon cohort found that adolescents who were frequently bullied were 2-3 times more likely to develop an anxiety disorder (odds ratio 2.49) (Stapinski et al. Depress Anxiety 2014;31:574-582). Anxiety was not attributable to comorbid depression. Individuals who endured frequent bullying were also more likely to develop multiple internalizing diagnoses in adulthood.

Prior studies have also found an association between bullying and later emotional problems. A two-year prospective study in Australian secondary schools interviewed 2,680 subjects twice at age 13, and once at age 14 (Bond et al. Br Med J 2001;323:480-484). A total of 51% of 13-year-olds reported some victimization. The prevalence of self-reported anxiety or depression was 18% at age 13, and 7% at age 14. Recurrent victimization was predictive of symptoms of anxiety and depression in girls (odds ratio 2.60) but not in boys (OR 1.36).

An interesting finding from a survey of 15-year-olds in Finland found that the risk of subsequent depression in boys was higher in bullies as well as in the bullied (Kaltiala-Heino et al. Eur Child Adolesc Psychiatry 2010;19:45-55). Being victimized was predictive of depression; conversely, depression was also predictive of being bullied and ostracized by peers.

In addition, several studies have found associations between bullying and self-harming behaviours. The Environmental Risk (E-Risk) longitudinal cohort study of twins aged 5-12 years in the U.K. found that among children who had self-harmed, 56% were victims of frequent bullying (Fisher et al. Br Med J 2012;344:e2683). Victimized twins were 2-4 times more likely to self-harm compared to their non-victimized twin. Similarly, the risk of self-harm was four-fold higher for boys who had been bullied in an analysis of an Irish cohort from the Child and Adolescent Self Harm in Europe (CASE) study (McMahon et al. Soc Sci Med 2010;71:1300-1307).

In the Finnish study cited above, being bullied at age 15 remained predictive of suicidal ideation at age 17 after controlling for symptoms of depression and internalization (Heikkila et al. Eur Child Adolesc Psychiatry 2013;22:95-102). Being a bully was modestly predictive of suicidal ideation in later life.