We know from yoga that one thing is always more than one thing. The world is more than one thing. Life is more than one thing. And so it is with health and disease. Narrowing it down further to the topic of bone density and osteoporosis, that too is more than one thing. Let's briefly look at a couple of the things.
We know that stress—that is, psychological and emotional forces—can be a factor. Prolonged excess cortisol can interfere with the bone building process and decrease bone density. See this article for more info.
We also know that physical stress is a big factor—the actual physical forces and loads you are under determine how your body builds bone and allocates resources. (The above article talks about that, as well.)
It isn't just how much weight you bear, though, but how you bear the weight. It's about posture and alignment, which directs how the forces are distributed through your tissues, and how much time you are under those loads. Biomechanist Katy Bowman talks about that here and here.
Also see Dr. Loren Fishman's 12-Yoga-Pose program for his take on bone density, which is slightly different from Katy Bowman's.
I'd like to point out something that both approaches hint at and draw that out further for emphasis. Bowman mentions mechanoreceptors, which are nerve receptors. That tells you that the nervous system and brain are involved. She also mentions posture or vertical alignment. And Fishman mentions balance. So one common factor there is your vestibular system.
Think about it like this. What happens to astronauts when they go into space? They get motion sickness. They lose bone density. They have trouble walking after returning to earth. And what measures where you are in space in relation to gravity? Your vestibular system (balance).
Fundamentally and reflexively, balance is controlled by your brain and nervous system based on input from your vestibular system. Posture is another way of saying that. Standing upright is reflexively controlled by your vestibular system (along with your vision and proprioception). The amount of load you are able to bear, your strength, is likewise based on your ability to balance and not fall over. Again, your vestibular system.
So it would make sense that osteoporosis and bone density might be improved by improving your balance and using it to walk with better alignment and feel less stress under the loads you carry. At least it would make sense to explore that as a possibility. There are other factors of course, as always, but they too will all be interrelated.