No type of cycling is going to increase bone density, but some types will decrease it. I listen to my knees and refuse to subscribe to the fashionable-on-forums low gearing which has been reappropriated from recommendations for elderly/injured riders.

BD is not a concern to me. Armchair Orthopedic conjecture really isn't of concern to me. I'm just shedding light on the other side of the coin. Sub-90gi riding on normal pave is neither fun nor physically advantageous to me.