People bullied by siblings during childhood are up to three times more likely to develop psychotic disorders such as schizophrenia in early adulthood, a study has found.
"Children spend substantial time with their siblings in the confinement of their family home and if bullied, this can lead to social defeat, self-blame and serious mental health disorder - as shown here for the first time," said Dieter Wolke from the University of Warwick in the UK.
In the study, published in the journal Psychological Medicine, almost 3,600 children completed a detailed questionnaire on sibling bullying at 12 years of age.
The participants then subsequently filled out a standardised clinical examination assessing psychotic symptoms when they were 18 years old.
Of the adolescents, 664 were victims of sibling bullying, 486 children were pure bullies to their siblings and 771 children were bully-victims (victimised by siblings and bullied their siblings), at age 12.
Fifty-five of the total 3,600 children in the study had developed a psychotic disorder by the age of 18.
The researchers found that the more frequently children are involved in sibling bullying - either as bully, victim, or both - the more likely they are to develop a psychotic disorder.
Those involved in sibling bullying (as bully or victim) several times a week or month are two to three times more likely to develop a psychotic disorder than other kids.
The children most at risk are victims of sibling bullying, and those who both become victims and bully their siblings (bully-victims).
Children who are victimised both at home and by school peers are even worse off - being four times more likely to develop psychotic disorders than those not involved in bullying at all.
"If the bullying occurs at home and at school the risk for psychotic disorder is even higher.
These adolescents have no safe place," said Slava Dantchev from the University of Warwick....