What Causes Malabsorption Of Calcium And Vitamin D In Body?

I am having trouble with my body absorbing calcium and Vitamin D - I have been diagnosed with Osteoporosis, it is a ‘bone’ breakdown condition that is not ‘repairing’ properly – a lot of people have it but mine has happened too quickly in a short period. It is a ‘calcium’ problem & I think I am not absorbing my good vitamins & calcium. Eye problem will be an ‘ongoing problem’ as we can’t find the cause -