Effect of Dietary Changes on Urinary Oxalate Excretion and Calcium Oxalate Supersaturation in Patients With Hyperoxaluric Stone Formation

Objectives

To test the hypothesis that patients with hyperoxaluria, who modified their dietary calcium intake, would reduce their urinary oxalate excretion without raising their urinary calcium excretion. Diet is a major factor in idiopathic calcium oxalate urolithiasis, yet controversy exists regarding the ideal clinical recommendations. Approximately 20% of patients with calcium oxalate stone formation have hyperoxaluria (≥45 mg oxalate/d). Calcium supplements to bind dietary oxalate have been suggested, but clinical evidence of this therapy is lacking.

Methods

Of 144 adult patients with stone formation seen by a registered dietitian from September 2006 to September 2007, 26 (18%) had hyperoxaluria on ≥1 24-hour urinalyses. Of those with ≥2 complete 24-hour collections and whose hyperoxaluria was observed before their last visit with the registered dietitian, 22 patients were identified. The patients were retrospectively separated into 2 groups according to whether they had been advised dietary changes alone (diet group, n = 10) or calcium citrate with meals, in addition to the dietary changes (supplement group, n = 12). The mean follow-up time was 317 and 266 days for the diet and supplement groups, respectively. Statistical comparisons within and between groups were made for urinary risk factors.

Results

Urinary oxalate excretion decreased from 56 to 43 mg/d and from 60 to 46 mg/d in the diet and supplement groups, respectively (P = .003 and P = .038, respectively). Calcium oxalate supersaturation decreased from 3.48 to 1.83 and from 2.37 to 1.52 in the diet and supplement groups, respectively (P = .043 and P = .002, respectively). Urinary calcium excretion did not change in either group.

Conclusions

Gastrointestinal binding of oxalate by calcium is an effective clinical strategy for hyperoxaluria, whether mediated by calcium citrate with meals or by inclusion of calcium-containing foods with meals.