Title: Effect of dietary modification on urinary stone risk factors
Abstract: To the Editor: Pak et al. retrospectively studied 951 stone formers and demonstrated reductions in urinary calcium excretion and urinary saturation of calcium oxalate following a diet limited in calcium, oxalate, sodium, and meat products. They suggest that calcium stone formers with urinary calcium >6.88 mmol/day restrict their dietary calcium intake to 10 mmol/day.1.Pak C. Odvina C. Pearle M. et al.Effect of dietary modification on urinary stone risk factors.Kidney Int. 2005; 68: 2264-2273Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar We disagree with this recommendation. In a 5-year randomized trial, Borghi et al. compared a low-calcium diet (10 mmol/day) to a diet without calcium restriction but low in salt and animal protein in 120 calcium oxalate stone formers with hypercalciuria (mean urinary calcium 11 mmol/day).2.Borghi L. Schianchi T. Meschi T. et al.Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria.N Engl J Med. 2002; 346: 77-84Crossref PubMed Scopus (733) Google Scholar The relative risk of stone recurrence in the usual calcium group, compared to the restricted calcium group, was 0.49 (P=0.04). Although this study did not address the independent role of dietary calcium restriction, it assessed actual kidney stone formation as the primary outcome rather than surrogate measures such as urinary saturation. In addition, secondary analyses of this trial confirmed the powerful effect of dietary sodium and animal protein restriction on reducing urinary calcium excretion. We remain concerned about the safety of dietary calcium restriction alone in patients with idiopathic hypercalciuria. Only a fraction of dietary calcium is absorbed.3.Frick K.K. Bushinsky D.A. Molecular mechanisms of primary hypercalciuria.J Am Soc Nephrol. 2003; 14: 1082-1095Crossref PubMed Scopus (115) Google Scholar Consumption of 10 mmol/day of calcium in a patient with urinary calcium losses of 6.5 mmol/day (the mean value from Pak's current study) may result in negative calcium balance and, over time, reduced bone mass.