May 8 (HealthDay News) -- Preteens who were bullied persistently when they were younger are more likely than others their age to have hallucinations, delusions or other psychotic symptoms, British researchers report.

Their study involved 6,437 youths, who averaged just less than 13 years old. Their parents had provided regular updates about the youngsters' health and development since birth, and the children had undergone yearly physical and psychological assessments since age 7.

About 46 percent of the youngsters experienced bullying at ages 8 or 10. As their neared 13, about 14 percent of the children had broad psychosis-like symptoms (one or more symptoms suspected or confirmed), 11 percent had intermediate symptoms (one or more symptoms suspected or present at times other than when going to sleep, waking from sleep, during a fever or after substance use) and 6 percent had narrow symptoms (one or more symptoms confirmed).

Children who were bullied at either ages 8 or 10 were about twice as likely as other children to have psychotic symptoms. The risk was highest in preteens who'd suffered chronic or severe bullying.

"Whether repeated victimization experiences alter cognitive and affective processing or re-program stress response, or whether psychotic symptoms are more likely due to genetic predisposition still needs to be determined in further research," wrote Andrea Schreier, of Warwick Medical School in Coventry, England, and colleagues.

"A major implication is that chronic or severe peer victimization has non-trivial, adverse, long-term consequences," they wrote. "Reduction of peer victimization and of the resulting stress caused to victims could be a worthwhile target for prevention and early intervention efforts for common mental health problems and psychosis."

The study appears in the May issue of the Archives of General Psychiatry.

SOURCE: JAMA/Archives journals, news release, May 4, 2009