Oral calcium carbonate affects calcium but not phosphorus balance in stage 3-4 chronic kidney disease

Area of Science:

• Nephrology
• Mineral and Bone Metabolism

Background:

• Patients with chronic kidney disease (CKD) often receive calcium carbonate to manage phosphorus levels and prevent negative calcium balance.
• Limited data exist on the precise effects of calcium carbonate on calcium and phosphorus balance in CKD patients.

Purpose of the Study:

• To investigate the effects of calcium carbonate supplementation on calcium and phosphorus balance in patients with stage 3 or 4 CKD.
• To assess calcium kinetics and potential soft tissue deposition associated with calcium carbonate use.

Main Methods:

• A randomized, placebo-controlled, cross-over study involving eight patients with stage 3-4 CKD.
• Controlled diet with and without calcium carbonate (1500 mg/day calcium) over two 3-week balance periods.
• Collection of all feces and urine; measurement of calcium kinetics using 45Ca; assessment of fasting blood and urine biochemistries.

Main Results:

• Patients were in neutral calcium and phosphorus balance on placebo.
• Calcium carbonate supplementation resulted in a positive calcium balance and a modest reduction in urinary phosphorus excretion.
• Phosphorus balance remained unaffected; calcium kinetics indicated positive net bone balance but also suggested soft-tissue calcium deposition.

Conclusions:

• Calcium carbonate supplementation in stage 3-4 CKD patients induces a positive calcium balance within 3 weeks.
• The lack of effect on phosphorus balance and potential for soft tissue deposition raise concerns about its long-term efficacy and safety as a phosphate binder.