Many children who are bullied suffer in silence. But there may be a way to identify victims of bullying before they suffer serious, long-term mental health problems, according to a recent study.

Researchers from the University of Warwick in the United Kingdom found that nightmares or night terrors could be a signal of a child being bullied. They found that nightmares were more common in 12-year-olds who had reported being bullied when they were 8 and 10 years old.

"Nightmares are relatively common in childhood, while night terrors occur in up to 10 percent of children," Suzet Tanya Lereya, lead author of the study and research fellow at University of Warwick, said in a statement. "If either occurs frequently or over a prolonged time period, they may indicate that a child/adolescent has or is being bullied by peers. These arousals in sleep may indicate significant distress for the child."

For the study, researchers analyzed data from the Avon Longitudinal Study of Parents and Children, which examined the determinants of development, health and disease during childhood and beyond. Children were enrolled at birth, and more that 6,400 were interviewed at ages 8 and 10 years about bullying and at age 12 about parasomnias, including nightmares, night terrors and sleep walking.

They found that at age 12 years, 1,555 (24.2 percent) of children had nightmares, 598 (9.3 percent) had night terrors, 814 (12.6 percent) reported sleep walking and 2,315 (36 percent) had at least one type of parasomnia (nightmares, night terrors and sleep walking).

Based on their findings, children who were victimized at 8 or 10 years were significantly more likely to have nightmares, night terrors or sleep walking at age 12. Moreover, those who were both a victim and a bully were much more likely to have any parasomnia, but bullies were not at increased risk of a sleep disturbance.

"Our findings indicate that being bullied is a significant stress/trauma that leads to increased risk of sleep arousal problems, such as nightmares or night terrors," Dr. Dieter Wolke, professor of developmental psychology and individual differences at University of Warwick, said in a statement. "It is an easily identifiable indicator that something scary is being processed during the night. Parents should be aware that this may be related to experiences of being bullied by peers, and it provides them with an opportunity to talk with their child about it."