I've never read studies about the subject but I am pretty sure you may find lots on the net. The simple fact that our governments spend good money on campaigns and all sorts of social help (toll free numbers etc...) denotes it.
But as I said I've never read about it though I've noticed 'something' about addiction.
I've learn and started to play poker on mature age, when I was 30+ already. I have like half a dozen friends and known people close to me that may have what is used to say 'gambling problems'. Sad thing I can tell you. One of them came to me last month asking for help to scan documents and ID's as he had to send it by email to one of these firms that lands money on big interest. All this because he needed to pay the rent end of the month and ALL his money from his regular day job was gone on
online poker. He entered in a kind o cycle of debts and from my point of view it is addiction likewise with cocaine or alcohol.
And it is not just this one, I have other close people with similar problems. One thing I found interesting is that they play poker and gamble since young age. I have a regular job, I don't live of poker but I love it, it's a passionate game and it is pretty much like a sport to me. But I may pass days without playing and I don't feel what these guys feel. It's for sure another relation with the thing.
I don't know for sure how the age factor plays here but in my experience and observation it does play a role when the matter is addiction as it does for addiction in general when it's about drugs and alcohol.
So, kiddos! Pay close attention to it!
About profitability: can poker be profitable and an addiction at once ? At least for those I observe in my quotidian life, no it is not possible. They just seem to not have the head for it.