I have a degree in both archeology and physiology –so I’ve looked at a lot of bones for a variety of reasons. For the moment, please ignore my whole organic cosmetic thing.
Human bodies are amazingly efficient. If you are not using your bones by pulling on them with your muscles, they really have no reason to lay down calcium and get stronger. SO – you can take all the calcium by mouth you want but if you are not using your muscles to pull on bones, the essential signal to your body to increase bones strength and density is not communicated. And why should it be?
One of the reasons we know this is true, is that when you look at skeletons you can almost tell their profession by the bumps on the bones where muscles attach: people who did a lot of physical labor had larger, denser bones with pronounced muscle attachment points. The wealthy (think nobles in Europe who had servants) tended to have finer, smoother bones with less density. And you should see the hand bones of pianist!
So when I see these dumb commercials selling calcium and drugs to reverse bones loss, I just want to scream. They don’t work well and many of them lay down a layer of a completely different mineral (not calcium) that is brittle and in no way protects you from breaking your hip or crushing a vertebra.
All humans, especially woman, should do 2 days a week of 20 minutes each session of weight training from 40 years on. It is the only way to ensure that you have safe bones as you age.