According to the websites I visited, alendronate works by "inhibiting osteoclasts (which are responsible for breaking down and reabsorbing bone). It strengthens bones by slowing down bone loss and allowing osteoblasts (bone-building cells) to work more effectively, improving bone mass."

So apparently it helps to slow down bone loss by inhibiting the cells that break down bone, thus allowing the cells that actually build bone to do their job better.

I look forward to finding out how well it works, which hopefully it does.