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Does Calcium Restriction Prevent Recurrence of Kidney Stones?

Patients with calcium oxalate kidney stones and idiopathic hypercalciuria frequently are told to reduce dietary calcium, despite a lack of evidence supporting this intervention. Moreover, other dietary modifications, including decreased animal protein and salt intake, may reduce stone recurrence. Therefore, Italian researchers randomized 120 men with recurrent calcium oxalate stones and idiopathic hypercalciuria to receive a normal-calcium diet (with reduced animal protein and salt) or a low-calcium diet (with no meat or salt restriction). All patients were told to drink plenty of fluids and to avoid oxalate-rich foods.

During 5 years of follow-up, cumulative incidence of stone recurrence was 20% in the normal-calcium group and 38% in the low-calcium group -- a significant difference. Urinary calcium levels dropped in both groups, but urinary oxalate levels decreased in the normal-calcium group and increased in the low-calcium group. Thus, calcium-oxalate saturation in the urine was significantly lower in the normal-calcium group than in the low-calcium group.

Comment: The interpretation of these results is complicated by the fact that 3 dietary variables were involved -- calcium, animal protein, and salt. However, the results suggest that dietary restriction of calcium is unnecessary, and probably deleterious, in patients with calcium oxalate stones. The presumed explanation is that dietary calcium binds oxalate in the intestinal lumen; when dietary calcium is restricted, intestinal oxalate absorption and urinary oxalate excretion increase accordingly.

— Allan S. Brett, MD

Published in Journal Watch General Medicine January 18, 2002

Citation(s):

Borghi L et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. N Engl J Med 2002 Jan 10; 346:77-84.

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