Researchers published figures in The BMJ journal to back anecdotal evidence that victimised teenagers often go on to struggle later in life.
They had trawled through the findings of a large project in Bristol, western England, that has tracked the health of 14,500 residents since the early 1990s.
In one phase of the project, nearly 4,000 participants completed a questionnaire at the age of 13, and were assessed again five years later for symptoms of depressive illness.
Out of 683 people who reported they had been bullied at least once a week at the age of 13, nearly 15 percent were depressed at 18.
This was nearly triple the rate for teenagers who had not been picked on.
Examples of bullying included kids being excluded by their peers, having lies spread about them, their belongings stolen, and being threatened, blackmailed or even beaten.
When other possible causes were added to the mix — such as behavioural or mental problems or family difficulties — the statistical link with adult depression weakened, but the rate was still twice as high as for non-bullied peers.
Among those frequently victimised, 10 percent experienced depression symptoms for more than two years, the study found. In the non-bullied group, only four percent suffered a depression lasting so long.
The team calculated that as many as 30 percent of depression cases identified in their study may have been the result of bullying, though the study could not show direct cause-and-effect.
Anti-bullying programmes in schools have been disappointing, noted the researchers.
“Interventions during adolescence could help to reduce the burden of depression later in life.” -AFP