Spending time online is normal behavior for teenagers. But too much Internet use by teens -- or too little, for that matter -- might be related to depression, a new study finds.
The findings, reported in the journal of Pediatrics, do not mean that the Internet is to blame. For one, teens in the study who spent no time online were also at increased risk of depression symptoms.
Instead, the researchers say that both heavy Internet use, and non-use, could serve as signals that a teenager is having a hard time.
For the study, Dr. Pierre-Andre Michaud and colleagues at the University of Lausanne, Switzerland, surveyed 7,200 individuals ages 16 to 20 about their Internet use.
Those who were online more than two hours per day were considered "heavy" Internet users, while those online anywhere from several times per week to two hours per day were considered "regular" users.
The teenagers also answered a number of health-related questions, including some standard questions about "depressive tendencies" that gauge how often a person feels sad or hopeless.
Compared with regular Internet users, the study found, kids who were heavy users or non-users were more likely to be depressed or very depressed.
Among male teens, heavy users and non-users were both around one-third more likely to have a high depression score, compared to "regular" users. Among girls, heavy Internet users had an 86 percent greater chance of depression, while non-users had a 46 percent greater likelihood compared to regular users.
That was with factors like family income and any chronic health problems taken into account.
However, the average depression scores among non-users, regular users and heavy users alike were all toward the lower end -- between 1 and 2 on a scale of 1 to 4, with 1 being "not depressed at all."
The authors of the current study didn't tell exactly how many kids in each group were depressed (and they didn't respond to a request for this information). A separate study from Switzerland published last year asked pediatricians in that country to estimate rates of mental health disorders in their young patients; the doctors estimated that the rate of depression in an average group of kids is 1.4%.
Exactly why both heavy Internet use and non-use were linked to higher depression risks is not clear, according to Michaud's team.
Since teenagers typically go online to connect with friends, the researchers speculate that those who are never online may be more socially isolated.
As for heavy Internet use, some past studies have also found links to depression symptoms -- for reasons that are unclear. But one study of Taiwanese teenagers found that depression symptoms typically preceded kids' heavy Internet use, Michaud and his colleagues point out.
In this study, certain other health concerns were also more common among heavy Internet users.
For males, weight was an issue: 18 percent of heavy users were overweight, compared with 12 percent of regular users. Among female teens, 59 percent of heavy Internet users were sleep-deprived, versus 35 percent of regular users.
As with the depression findings, though, it's not clear why those relationships existed.
In the case of sleep loss, the researchers say, it may be that some teenage girls trade bedtime for online time. As for boys' excess pounds, it's not clear whether sedentary computer time boosts weight gain, or whether overweight teens are apt to spend more time in front of the computer.
The bottom line, according to Michaud's team, is that either excessive time online, or little to no time online, could be indicators that a teenager is having problems.
On the other hand, the researchers note, regular Internet use -- up to two hours per day in this study -- appears to be "normal" teen behavior.
They point out, though, that the study was conducted in 2002, before the days of Facebook and Twitter. Many teenagers now may spend much more time online, and the definition of "normal" time could also be different.