The study led by the University of Oxford asked around 7,000 children aged 12 if they had experienced a sibling saying hurtful things, hitting, ignoring or lying about them.

The children were followed up at 18 and asked about their mental health. Researchers from the Universities of Oxford, Warwick and Bristol and University College London sent questionnaires to thousands of families with 12-year-old children in 2003-04 and went back to them six years later to assess their mental health.

Most children said they had not experienced bullying. Of these, at 18, 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.

The 786 children who said they had been bullied by a sibling several times a week were found to be twice as likely to have depression, self-harm and anxiety as the other children, 'BBC News' reported.

In this group, depression was reported by 12.3 percent, self-harm by 14 percent, and 16 percent of them reported anxiety.

Girls were slightly more likely to be victims of sibling bullying than boys, particularly in families where there were three or more children.

On average, victims said that sibling bullying had started at the age of eight, according to the study.

Lead author Dr Lucy Bowes, from the department of social policy and intervention at the University of Oxford, said although they couldn't say sibling bullying caused depression, the result were significant.

"It may be causing long-term harm. We need to do more research, but we also need parents to listen to their children.

"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," she said.

Latest News from Lifestyle News Desk