So far they have only guesses. They have ruled out a few things, like hereditary being a risk thankfully, but that is about it.

It is a build up of proteins in a particular portion of the brain. NOT iron, as the second link above implies. That story is making a broad guess that since excessive iron is bad for the brain cells in general, it can be tied to LBD.  

I also note that it is on a site that is for cocaine addiction treatment. They add it as a scare tactic. That alone makes me skeptical about anything they say.

The other link is more credible, but still a lot of speculation. It is also talking about Parkinson, which like LBD is caused with protein buildup in the brain, but in a different area. 

I think of LBD and Parkinsons as being cousins, but they are not the same disease. Neither one causes the other.

Any drug addiction causes some damage to the body. The slight correlation they are implying may be no more than less healthy people tend to have more problems in general. The weakness of the body from the one makes the body less able to fight off something else. 

And I will tell you the God's Honest Truth: If I were to get LBD, I would want to die before they symptoms start. If Robin did find out he had LBD and decided to kill himself, I fully understand.