Teenagers who are obsessed with Internet are more likely to become depressed, scientists have claimed, suggesting schools should watch out for early symptoms.

Researchers from Australia and China found teenagers who feel anxious or nervous when they are not on the Internet, called a pathological habit, are two and a half times more likely to develop depression, the Telegraph reported.

The scientists, who examined over 1,000 teenagers with an average age of 15, asked them about their Internet use.

They found that just over six per cent of the teenagers were pathological users of the Internet, who said they felt depressed, moody or nervous when not on the Internet but this disappeared when they were back online.

At the beginning of the study, none of the participants had depression. But nine months after when the teenagers were examined again for signs of anxiety or depression, it was found that the pathological Internet users were two and half times more likely to show signs of the condition than those who used the Internet normally.

Detailing their findings in the journal 'Archives of Paediatrics & Adolescent Medicine', the authors led by Lawrence Lam, of the School of Medicine in Sydney, wrote: "This result suggests that young people who are initially free of mental health problems but use the Internet pathologically could develop depression as a consequence.

"As we understand that mental health problems among adolescents bear a significant personal cost as well as costs to the community, early intervention and prevention that targets at-risk groups with identified risk factors is effective in reducing the burden of depression among young people.

"Screening for at-risk individuals in the school setting could be considered an effective early prevention strategy according to recent meta-analysis.

Hence, a screening programme for pathological use of the Internet could also be considered in all high schools to identify individuals at risk for early counselling and treatment."

However it cannot be known if teenagers who have a tendency to depression are more likely to be obsessive about the Internet rather than the Internet being the cause of their depression.