Those who self-harm as teenagers are more at risk of developing mental health problems as adults, new research in Britain from the biggest study of its kind has revealed.

The study, published in the latest issue of British Medical Journal on Thursday, reveals that almost a fifth of 16-year-olds who took part in the study had a history of self-harm and most had not sought help from health professionals.

Researchers at Bristol University, the University of Oxford and University College London, collected data from 4,799 adolescents as part of the longitudinal study Children of the 90s, one of the largest population studies ever performed, to examine the outcomes of self-injury for the first time.

Observing their progress over a five-year period showed that even those who self-harmed without suicidal intent had an increased risk of developing mental health problems, such as depression and anxiety, compared with adolescents who had not self-mutilated.

They were also more likely to self-harm in the future and to have substance abuse problems, such as using illegal drugs, smoking and drinking too much.

"We've shown that adolescents who self-harm are more vulnerable to a range of adverse conditions in early adulthood," Dr Becky Mars from Bristol University, who led the research, said: "While we cannot say that self-harm directly causes such problems, it's certainly a sign that all is not well, and professionals need to be aware of such behaviour and identify it early."

Experts believe these new findings highlight the importance of self-harm and the need for better understanding among professionals likely to come across youngsters who engage in it.