I think you guys are looking at this from the wrong direction. This isn't like the ridiculous stories about bagels causing cancer from a while back. There is a very important difference between being alone, which can be refreshing and relaxing, and being lonely. Loneliness in this context is more akin to things like depression and stress, where your physical condition can start to reflect your psychological state. As such, the assumed causal connection described in the original post makes perfect sense to me.