Post-menopause, I had a dexa scan that showed that I was losing bone mass. My doctor didn't seem to think it was significant. 15 months later I saw a different doctor who said you should start taking Actonel right away; I had osteopenia in my spine, with some vertebra in the osteoporosis range. No side effects were discussed at all.
I am reluctantly taking Actonel right now but I found this website:
Dr. Loren Fishman studied Iyengar yoga for years before he went to medical school and he is now a physiatrist. He advocates using yoga as a weight-bearing exercise if you hold each pose for 30 seconds or longer. He took 12 yoga poses and shows how you can gradually learn them while being gentle on your bones. I highly recommend you take a look!
Note from Kate: Please read the yoga caution page before starting yoga is you have Osteopenia/Osteoporosis. Yes, it can be helpful...but it can also be dangerous. See: