People who spend a lot of time surfing the Internet are more likely to show depressive symptoms than those who don't.

Research by University of Leeds psychologists found that some users have developed a compulsive habit that replaces real-life social interaction with online chat rooms and social networking sites. The results suggest that this type of addictive behavior can have a serious impact on mental health.

"The Internet now plays a huge part in modern life, but its benefits are accompanied by a darker side," said lead author Dr. Catriona Morrison. "While many of us use the Internet to pay bills, shop and send emails, there is a small subset of the population who find it hard to control how much time they spend online, to the point where it interferes with their daily activities."

"Our research indicates that excessive Internet use is associated with depression, but what we don't know is which comes first -- are depressed people drawn to the Internet or does the Internet cause depression?" Morrison noted. "What is clear, is that for a small subset of people, excessive use of the Internet could be a warning signal for depressive tendencies."

In the Leeds study, young people were more likely to be Internet addicted than middle-aged users, with 21 years being  the average age of the addicted group.

"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 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."