Adults who were bullied as children are at an increased risk of developing depression and anxiety, as well as experiencing suicidal thoughts, a new long-term study suggests.

According to the UK and US scientists who carried out the study, the findings indicate that the effects of bullying are not something that a person simply outgrows.

They followed the progress of almost 1,500 children for around two decades. The children were aged nine, 11 and 13 at the start of the study and they and their parents were interviewed every year until they were 16. They were then interviewed periodically after that.

Up until the age of 16, the children and their parents were asked about any bullying that had taken place in the three months prior.

Around one in four were found to have been bullied at least once and this was the same for both boys and girls. Almost one in 10 admitted to being a bully.

When they were followed up in adulthood, the scientists found that those who had been bullied were at an increased risk of suffering some kind of psychiatric disorder compared to those who had never been bullied. They had higher levels of depression, anxiety disorders and panic disorders.

Those who had been bullies were also at an increased risk of having an antisocial personality disorder.

"We were surprised at how profoundly bullying affects a person's long-term functioning. This psychological damage doesn't just go away because a person grew up and is no longer bullied. This is something that stays with them. If we can address this now, we can prevent a whole host of problems down the road," commented lead scientist, Dr William Copeland, of Duke University in the US.

The team believes that these are the most definite findings to date on the long-term effects of bullying.

"Bullying, which we tend to think of as a normal and not terribly important part of childhood, turns out to have the potential for very serious consequences for children, adolescents and adults," the added.

Details of these findings are published in the journal, JAMA Psychiatry.