Yes- there are many causes.
Here's my two cents worth.
In many cases (dare I say a majority of cases!) of osteoporosis the cause is not so much not taking in enough calcium but rather a leeching of the calcium from the bones.
Now, due to your low calcium levels you need to understand the concept of 'negative calcium balance'.
Do some research on this and you will understand (basically it means that more calcium is excreted in the urine than is absorbed through digestion). A negative balance over time means decreases in bone density- the body must find additional calcium and so it draws it from the primary calcium stores -the bones.
Studies have linked osteoporosis (not to low calcium intake) but to nutritional factors which cause the excessive calcium loss in urine.
So study up on negative calcium balance and you may find that your nutritional/dietary habits are the cause of your low calcium levels.
Hope this helps.
Cheers
brett
(nutritional-supplement-truths.Com)
