Psychologists at the University of Leeds say people who spend a lot of time browsing the internet are more likely to show depressive symptoms.

In a study to be published in the journal Psychopathology next week, researchers documented evidence that some users have developed a compulsive internet habit, whereby they replace real-life social interaction with online chat rooms and social networking sites. The results suggest that this type of addictive surfing can have a serious impact on mental health.

 The internet use and depression levels of 1,319 people aged 16-51 were evaluated for the study. Of these, 1.2% were classed as being internet addicted. While small, this figure is larger than the incidence of gambling in the UK, which stands at 0.6%.

These 'internet addicts' spent proportionately more time browsing sexually gratifying websites, online gaming sites and online communities. They also had a higher incidence of moderate to severe depression than non-addicted users.

While a link was found between excessive internet use and depression symptoms, the researchers are unsure which comes first, said lead author Dr Catriona Morrison. "Are depressed people drawn to the internet or does the internet cause depression?"

"What is clear, is that for a small subset of people, excessive use of the internet could be a warning signal for depressive tendencies."

Incidents such as the spate of suicides among teenagers in the Welsh town of Bridgend in 2008 led many to question the extent to which social networking sites can contribute to depressive thoughts in vulnerable teenagers. In the Leeds study, young people were more likely to be internet addicted than middle-aged users, with the average age of the addicted group standing at 21 years.

"This study reinforces the public speculation that over-engaging in websites that serve to replace normal social function might be linked to psychological disorders like depression and addiction," added Dr Morrison. "We now need to consider the wider societal implications of this relationship and establish clearly the effects of excessive internet use on mental health."