Purpose: Patients with calcium renal stone are reported to have lower bone mineral density. The state of bone density in patients with renal stones have different explanations but the role of nutritional factors seems to be crucial. A group of 48 consecutive male calcium renal stone formers was studied to investigate the relationship between bone density and dietary intake.
Materials and methods: Patients completed a dietary diary for a 3-day period during normal diet. Nutrients and calories were calculated by food composition tables using a computerized procedure. Bone densitometry was assessed at the lumbar spine and femoral neck, and expressed as Z score. A blood sample was collected and was analyzed for serum biochemistry including alkaline phosphatase, parathyroid hormone and 1,25 vitamin D. A 24-hour urine sample was analyzed for calcium, phosphate, oxalate, citrate and other electrolytes.
Results: Dietary calcium intake was significantly lower (p < 0.01) in patients with low than in those with normal bone mineral density. There was no difference in serum parathyroid hormone levels, phosphate and alkaline phosphatase between the 2 groups. The results suggest that some renal stone formers seem to be unable to decrease renal excretion of calcium on a low calcium diet leading to a negative calcium balance.
Conclusions: A primary abnormality of bone metabolism could be a reasonable explanation of reduced bone density observed in renal stone formers on a low calcium diet since serum parathyroid hormone levels are in the normal range. From a therapeutic point of view these data confirm that restriction of dairy products in renal stone formers should be avoided.