Stone forming risk of calcium citrate supplementation in healthy postmenopausal women

Purpose: We evaluated the effect of calcium citrate supplementation alone or in combination with potassium citrate on the stone forming propensity in healthy postmenopausal women. Materials and Methods: A total of 18 postmenopausal women without stones underwent a randomized trial of 4 phases comprised of 2 weeks of treatment with placebo, calcium citrate (400 mg calcium twice daily), potassium citrate (20 mEq twice daily), and calcium citrate and potassium citrate (at same doses). During the last 2 days of each phase urine was collected in 24-hour pools for complete stone risk analysis. Results: Compared to placebo, calcium citrate increased urinary calcium and citrate but decreased urinary oxalate and phosphate. Urinary saturation of calcium oxalate, brushite and undissociated uric acid did not change. Potassium citrate decreased urinary calcium, and increased urinary citrate and pH. It decreased urinary saturation of calcium oxalate and undissociated uric acid, and did not change the saturation of brushite. When calcium citrate was combined with potassium citrate, urinary calcium remained high, urinary citrate increased even further and urinary oxalate remained reduced from the calcium citrate alone, thereby marginally decreasing the urinary saturation of calcium oxalate. Urinary pH increased, decreasing urinary undissociated uric acid. The increase in pH increased the saturation of brushite despite the decrease in urinary phosphorus. Conclusions: Calcium citrate supplementation does not increase the risk of stone formation in healthy postmenopausal women. The co-administered potassium citrate may provide additional protection against formation of uric acid and calcium oxalate stones.