Rarely do siblings grow up without engaging in a rivalry, which can be healthy until it crosses the line into a different territory - Bullying. Being bullied by a sibling during one's formative years can lead to mental health problems as an adult, says a new study led by researchers at the Warwick University.

Unfortunately, bullying is a common issue among school-going children and can manifest in physical, verbal or emotional forms. Between 1 in 4 and 1 in 3 students in the U.S. say they have been bullied at school. The most familiar imagery, as seen in movies and TV shows, depict young students being slammed into lockers or having their lunch money stolen by means of intimidation.

But what happens when a child has to deal with such behavior within the space of their own family and home?

"Children spend substantial time with their siblings in the confinement of their family home and if bullied and excluded, this can lead to social defeat and self-blame and serious mental health disorder - as shown here for the first time," explained Professor Dieter Wolke, who is from the University of Warwick’s Department of Psychology. Bullying by siblings "has been until recently widely ignored as a trauma that may lead to serious mental health problems such as psychotic disorder," he added.

The study examined 6,988 participants of both parents and children, first by filling out a detailed questionnaire at the age of 12 followed up by a standardized clinical examination at the age of 18. Among the 12-year old participants who took the test, 664 were pure victims of sibling bullying, 486 were pure bullies to their siblings and 771 were both victims and perpetrators of sibling bullying.

By the time they came of age, it was discovered that 55 of the total 3,600 children had developed a psychotic disorder. Such a disorder could involve a loss of touch with reality, abnormal thinking patterns, schizophrenia etc.

Results of the semi-structured interviews suggested that a higher frequency of exposure to bullying (either as the bully, as the victim, or both) led a higher risk of developing mental health problems later in life. Children who were "victimized in more than one context (home and school) were at the highest odds of meeting criteria of a psychotic disorder."

Lead author and doctoral student Slava Dantchev explained that without a relieving outlet at school or at home (i.e. friends or family), the adolescents would "have no safe place", thus resorting to emotional repression. The study details how childhood trauma creates a lasting ‘cognitive vulnerability’ in the brain where bullying was found to increase one's sensitivity to stress. 

"Our study adds that children involved in sibling bullying are at increased risk of developing a psychotic disorder, in keeping with findings for other kinds of stressors during childhood," the researchers stated. "If causal, as suggested by our study, this highlights the need for parents and health professionals to identify and put into place mechanisms to minimize sibling bullying within families."