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CHICAGO, May 4 (Reuters) - People who are bullied as children have twice the risk of having delusions, hallucinations or other psychotic symptoms as pre-teens as those who have not been bullied, British researchers said on Monday.

They said bullying -- especially when it is severe or chronic -- can have serious consequences for some children, and may even act as a trigger for people who are genetically predisposed to schizophrenia.

"Chronic or severe peer victimization has nontrivial, adverse, long-term consequences," Andrea Schreier of the University of Warwick in Coventry, England, and colleagues wrote in the Archives of General Psychiatry.

Several studies have shown that traumatic events in childhood such as physical or sexual abuse are linked with the development of psychosis in adulthood. And people who display psychotic symptoms in childhood are more prone to develop schizophrenia as adults.

Schreier and colleagues wanted to see if bullying might bring about some of these symptoms in adolescents. They studied 6,437 12-year-olds who underwent yearly physical and psychological assessments from age 7 and whose parents regularly filled out surveys.

At each visit, trained interviewers rated the children on whether they had experienced psychotic symptoms such as hallucinations, delusions or thought disorders during the prior six months. Children, parents and teachers reported on whether the child had been bullied -- as defined by negative actions by one or more other students with the intention to hurt.

A total of 46.2 percent of participants were considered victims of bullying when they were 8 or 10.

They found that the appearance of psychotic symptoms was twice as high among the victims of bullying, regardless of whether they had any psychiatric illness, family trouble or their level of intelligence. This link was stronger when the bullying was chronic or severe.

It is not yet clear how bullying raises the risks for psychotic behaviors in adolescents, but it may be that bullying brings out such behaviors in people who are already genetically predisposed to schizophrenia, they said.

Or it may be that repeated bullying alters a person's ability to respond to stress.

That needs more study, but intervention programs aimed at reducing bullying may help prevent some psychiatric problems later on, they said.

(Editing by Philip Barbara)