Not all internet addicts have issues with depression, but I do believe that most people who have issues with depression are internet addicts, because of the social anxiety that's 'linked' to depression.
It feeds the beast.
I think those of the internet-obsessed have moments where they assess the reality of their lives after being immersed in the online universe, then deem the assessment as unsatisfactory. It's not a motivating assessment, especially to anyone pre-disposed to depression. It can be a safe zone, and it can also be a vicious circle. Does it cause depression? Maybe in certain instances where a person requires the outside world, but is simply choosing to neglect it. Does it further deepen depression? I'd say damn straight it does. It gives the illusion of functioning, but it can be better than certain alternatives regarding mental state.
Hang on traveling woman - Don't sacrifice your plan
Cause it will come back to you - Before you lose it on the man
Yes. Generally these types of links usually have causation going both ways, sometimes to a confusing, chaos theory degree.
It's pretty obvious how causation could go either way. Depressed people being too unmotivated or lacking the self-esteem to do much beyond surf the internet. Just as other forms of escapism can serve as short-term release. Then there's people who use the internet to such a degree that it interferes with metal and physical functioning conductive to happiness. The same thing that happens with excessive eating, sleeping, watching TV, work, exercise etc.
There are plenty of other possibilities that shouldn't be ignored. Even unusual ones, like screens shining light directly into eyes causing hormonal imbalances or something.
Anyway, studies like this have to be done. Often the supposed link turns out to be a myth, but when it's established (which it isn't), more specific studies can try to find out exactly what's going on.
"Moderate computer use or TV time linked to early death"
"…anyone who devotes more than four hours daily on screen-based entertainment such as TV, video games or surfing the web, ups their risk of heart attack and stroke by 113 percent and the risk of death by any cause by nearly 50 percent compared to those who spend less than two hours daily in screen play — and this is regardless of whether or not they also work out."
I'd definitely be hitting up a couch or park bench just to stare at nothing for at least half the time spent at this computer.
There weren't sheep to kick in the ass after in america 50 years ago, so I wonder if heavy smoking and driving cars (while seated) powered by leaded fuel helped them reach their mid-60s, or what's most likely a younger average deathrate than what we have now.