Chronic PPI usage is associated with an increase occurrence of bone fractures, at present, the likely mechanism of this affect, is not at all clear.
The assumed mechanism is that long-term PPI use leads to decreased intestinal absorption of calcium resulting in negative calcium balance, increased osteoporosis, development of secondary hyperparathyroidism, increased bone loss and increased fractures.
An acidic environment in the stomach facilitates the release of ionzed calcium from insoluble calcium salts, and the calcium solubilization is thought to be important for calcium absorption.
That's all!
Happy studying!
-IkaN