Research studying competitive cyclists suggests that cycling can reduce bone density.
… most recreational cyclists probably don’t need to worry too much about their bones. “The studies to date have looked primarily at racers,” [researcher Aaron] Smathers says. “That’s a very specialized demographic. These guys train for hours at a very high intensity. They sweat a lot. They never go for runs. They don’t usually do much weight-lifting,” to avoid adding bulk. “They’re strange.”
I never “train for hours at a very high intensity,” so I’m probably safe.