Sep 19, 2014 12:36 PM EDT By J Baulkman, UniversityHerald Reporter

Children who are bullied by their brothers and sisters several times a week or more during adolescence are significantly more likely to be clinically depressed as young adults, according to a recent study.

Researchers from the University of Oxford found that those bullied by their siblings are twice as likely to report being depressed and to say they had self-harmed within the previous year compared with those who had not been bullied.

"Victims of sibling bullying are offered little escape as sibling relationships endure throughout development," Lucy Bowes, lead author of the study, said in a statement. "We are not talking about the sort of teasing that often goes on within families, but incidents that occur several times a week, in which victims are ignored by their brothers or sisters, or are subjected to verbal or physical violence."

For the study, researchers collected and analyzed data from nearly 7,000 children of women who enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC) in the 1990s. Study participants completed postal questionnaires in 2003 and 2004 about whether they had experienced any form of sibling bullying and if so, how often it happened.

The same children were followed up at the age of 18 years, so their mental health could be assessed using a validated online questionnaire, known as the Clinical Interview Schedule. The teenagers attended a clinic to fill in the questionnaire that asked them about their feelings and any recent self-harming behavior.

Of the 3,452 children with information on both sibling bullying and psychiatric outcomes, 1,810 said they had not been bullied by a brother or sister. Of these, 6.4 percent had depression scores in the clinically significant range, 9.3 percent experienced anxiety and 7.6 percent had self-harmed in the previous year. Of the 786 children who said they had been bullied by a sibling several times a week, clinical depression was reported by 12.3 percent, 14 percent had self-harmed in the previous year and 16 percent of them reported anxiety.

The link between being bullied by their siblings as a child and later mental health disorders was found to be similar for both boys and girls.

"Social learning and how to behave with peers starts at home, and when siblings are bullied it can have serious long- term consequences as we found in our study," Dieter Wolke, co-author of the study, said in a statement. "It is important that parents set clear rules about what is allowed in conflicts and they should intervene consistently when their children maltreat each other repeatedly."

The findings were recently published in the journal Pediatrics. 

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