Preventing childhood bullying may also help curb the need for treatment of psychiatric problems in early adulthood, suggests a new study that followed more than 5,000 children in Finland.

Researchers found that being frequently bullied at age eight, or having been both bullied and a bully, were each tied to a doubled risk of having psychiatric problems requiring treatment as a young adult.

"I think this is an important finding which should be taken seriously," said lead author Dr. Andre Sourander, of the University of Turku.

In the U.S., about one in four students report being bullied during the school year, according to the National Bullying Prevention Center.

Sourander and his colleagues write in JAMA Psychiatry that increasing evidence suggests bullying and being bullied contribute to later mental health issues, but few large studies have examined the question over time.

The researchers used data collected in 1989 from 5,034 eight-year-old participants who answered surveys about bullying. The children's parents and teachers also reported whether the children were being bullied or bullying others.

Overall, about 90 percent of children had no experience of bullying in either role. Another 3 percent were bullies, 5 percent were bullied and 2 percent were both bullies and bullied.

The researchers then analyzed information from a national health database about the same children when they were between the ages of 16 and 29 years old, looking to see if they had received treatment or services for psychiatric disorders like schizophrenia, depression, anxiety or substance abuse.

About 12 percent of people who had not been bullies or bullied received treatment or services for psychiatric disorders later in life. That compared to about 20 percent among bullies, about 23 percent among people who were bullied and about 31 percent who were both bullied and bullies.

Researchers found that compared to those with no exposure either way, being bullied as a child was linked to 1.9 times the risk of needing psychiatric treatment and services later in life, after adjusting for other factors that may also be linked to risk for psychiatric problems. Among those who were both bullied and bullies, the risk in adulthood was 2.1 times that of those with no exposure.

Most bullies in the study were boys and had existing psychiatric symptoms at age eight, the researchers note. And being a bully was specifically linked on its own to later psychiatric problems if there were already symptoms of disorders detected in childhood.

Being a bully, the study team writes, "serves as an important red flag" that the child needs some sort of intervention to prevent and improve downstream effects.

"It's converging with some other findings in the field that there are some very important mental health concerns that are linked to bullying," said Catherine Bradshaw, an expert on bullying from the University of Virginia in Charlottesville and the Johns Hopkins Center for the Prevention of Youth Violence in Baltimore.

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Researchers caution that this study can't explain how being exposed to bullying - either as a victim or perpetrator - may have led to later psychiatric disorders among kids in the study.

There could be a number of reasons for the link between bullying exposure and mental health problems, said Bradshaw, who was not involved in the research. "There could be many pathways some biological and others that are more social," she said.

Sourander told Reuters Health that being bullied is traumatizing for children.

"We need to understand how important early peer and school experiences are for children," he said by email. "We should integrate school mental health perspective to antibully campaigns. Early intervention can prevent long-term consequences."