By Mo McNulty
(Image: Twentyfour Students via flickr)
Bullying has long been recognized as a public health problem, with both victims of bullying as well as the bullies themselves experiencing health problems such as headaches and anxiety. Additionally, other studies show that bullying victims are more likely to consider suicide, and a large proportion of suicides among young people are likely linked to bullying. Now, a new study published in the BMJ has found that negative health effects caused by bullying persist for years; children who had encountered peer victimization experienced higher rates of depression as young adults.
Oxford researcher Lucy Bowes and her colleagues conducted a longitudinal observational study: they collected data on the same subjects over time. Their subjects came from the ALSPAC cohort, a group of British children who have been followed since before birth.
Bowes et al. interviewed children at the ages of 8, 10, and 13 to see how often they experienced different types of bullying. The researchers then followed up with a subset of the children five years later to determine how many experienced symptoms of depression. They found that children who were frequently victimized were more likely to be depressed at the age of 18. Furthermore, there was a dose-dependent association between bullying and depression: subjects who were bullied often were more likely to report depression than those who were only bullied occasionally.
Here’s a table showing the proportion and odds ratios of depressed teens, based on how frequently they were bullied. Their authors presented their data in both unadjusted form, as well as adjusted for various confounding factors:
The researchers also calculated the population attributable fraction, which is the amount that a given risk factor contributes to a disease. They found that 29.2% of the risk of young adult depression in their cohort could be explained by childhood bullying.
Because this was an observational trial, it was impossible for the researchers to directly determine whether the relationship between bullying and depression is causal. However, their evidence does support this notion. Additionally, the authors noted that there might be some bias in their study, as 18 year-olds from more wealthy, educated families were more likely to return to the clinic. Therefore, the sample of young adults that was tested for depression may have had different characteristics than the starting sample of children in which bullying was measured.
Although other studies have previously shown similar links between bullying and later mental health problems, this study is by far the biggest; as a result Bowes et al. were better able to adjust for some confounding factors that had limited previous studies. This study indicates that bullying prevention programs are an important public health intervention.
Bowes L, Joinson C, Wolke D, Lewis G. Peer victimisation during adolescence and its impact on depression in early adulthood: prospective cohort study in the United Kingdom. BMJ 350, h2469 (2015). PMID: 26037951