Accumulating evidence indicated that renal calcium stone formers often exhibit a low bone density. Therefore we want to test the hypothesis, that the mineral (calcium) metabolism is differently regulated in calcium stone formers with low as opposed to high bone density.

There is epidemiological evidence associating renal calcium stones and decreased bone mineral density (BMD). The decreased BMD in calcium stone formers is linked to hypercalciuria and both subtypes, fasting as well as absorptive hypercalciuria are associated with a diminished BMD. Higher 1,25-vitamin D plasma concentrations and lower PTH levels are encountered under free-choice diet conditions in patients diagnosed with absorptive and fasting hypercalciuria when compared to normocalciuric stone formers. Reports studying the BMD of stone formers and its link with mineral metabolism variables and urinary calcium excretion under different calcium intakes are rare.

We hypothesize now that PTH and 1,25-vitamin D change differently when calcium stone formers with high, intermediate and low BMD are challenged by a low calcium diet.

Inclusion Criteria:

• passage of at least one calcium containing kidney stone

Exclusion Criteria:

• established cause of calcium stone formation (sarcoidosis, primary hyperparathyroidism etc.)
• creatinine clearance < 60 ml/min
• urinary tract infection

Recurrent renal calcium stone formers