I've had pretty much everything, since I'm a horror writer. However, I don't think just the inclusion of dark elements is enough to make something effectively disturbing. You really have to care about the characters, and they also really have to care. For example, my last novel culminated in a 16 year old boy being raped and killed. It was the "heaviest" part of my story, but the most disturbing part to myself and to most of my readers was a scene slightly before the event, where the killer knows what he is going to do, and is dangerously drunk in preparation for it with his infant daughter in his lap. He sort of picks up the baby and muses to himself that she probably weighs a tenth what his victim weighs, and for second tries to hold her completely still while she's struggling, to see how hard it will be to hold his victim down. he doesn't harm the little girl in any way, but just the idea of him using her to measure something like that really freaked a lot of readers out.
The series I am working on now includes orphans/poor people being used for "spare parts" during a horrible outbreak of disease (sort of like a medical version of "a modest proposal" wink