How depression develops in children

When children bully other children at school, it usually takes the form of physical attacks or insults. According to studies, around ten percent of all children and young people who experience such behaviour are persistently or chronically victimised by their peers, i.e. they are «made victims» and thus harmed.

These children show symptoms of depression more often than children who are left alone. For example, they are often sad or have a negative outlook on the future. As part of our research, my colleagues and I have discovered the effects that the immediate physical response to the stress of a negative experience can have. Our findings may help explain the biological links between negative experiences with peers and the development and duration of depression.

Violence causes stress

Threats and bullying by peers at school are a major problem for many children . Numerous studies indicate that children who are victimised also report depression. However, the exact processes that establish this link are less clear. To better understand these connections, we chose the so-called experience sample as our methodological approach in our recently published study, which captures the feelings of the test subjects at a specific point in time.

We asked 100 schoolchildren aged between ten and eleven to keep a short diary five times a day over four school days. The diary included questions about how negative their experiences with their peers were at that moment. At the same times, they gave us saliva samples so that we could measure their cortisol levels. The hormone cortisol plays a role in our body's fight-or-flight response to stress.

How severe is the depression?

The children also indicated whether they felt harassed by their peers and answered questions designed to measure the severity of their depression. We used the data to disentangle the individual factors involved in the link between peer victimisation and depression – beyond the immediate stress response of the children.

In most children in this study, greater victimisation by peers was associated with higher cortisol levels. This suggests that the children felt stressed by the bullying they experienced from their classmates.

Children who are constantly victimised report depressive symptoms more frequently.

However, in the ten percent of children who reported being frequently or constantly victimised by their peers, the cortisol response to negative experiences decreased. Such an underreaction can also be observed in abused animals or victims of domestic violence. This shows that the response adapts to constantly recurring acute stress. The same effect can be seen in people with persistent depression.

Children react differently

Accordingly, children who are constantly victimised show a more subdued immediate physiological response to negative experiences and also report depressive symptoms more frequently.

The results point to two findings: people differ in their immediate reactions to negative experiences and, more importantly, these differences may help explain the links between negative social experiences (such as victimisation) and mental health (as manifested in symptoms of depression).

There is a link between bullying by classmates during childhood and the severity of depression. The effects can sometimes last into adulthood. Our research findings indicate that interventions against bullying in schools must take into account the stress levels of pupils at the time of the negative experience.

Many of today's interventions aim to develop social skills. While these are very important, they appear to be only part of the equation. Our study provides evidence that the profound effects of negative peer experiences may be attributable to physiological stress responses.

By helping students process their reactions to negative experiences with their peers in the moment they occur, we can ultimately reduce the symptoms of depression throughout their lives.