Spending too much or too little time online may increase depression in young people, according to a Swiss study. Research at the University of Lausanne has found young people aged 16 to 20 who spend more than two hours per day online are at an increased risk of depression symptoms. But so are teens who don't log on at all.

The study surveyed 7,200 young people about their Internet habits and then asked them a series of health-related questions that focused on depressive tendencies and symptoms such as weight, headaches, back pain and sleep loss. Youth who spend more time online more often have feelings of sadness or hopelessness, the study found.

Compared with young people who are considered "regular Internet users" - logging on several times a week for up to two hours at a time - the heavy users and non-users are more likely to be classified as depressed or very depressed, the researchers said.

Male users were more likely to have a high depression score. Heavy users were also found to be at an increased risk of being overweight or suffering from sleep loss.

The research team said it's not clear why heavy Internet use and non-Internet use are both linked to higher risks of depression. But the study speculates the online use at both ends of the spectrum may be indicative of feelings of isolation among the teens.

The researchers added the results need further study because the surveys were conducted before 2002, and the advent of social networking sites, such as Facebook and Twitter.