Calcium Carbonate: Clinical Uses and Dosing
Calcium carbonate serves two primary roles: as an antacid for symptomatic relief and as a calcium supplement for bone health, with standard dosing of 1000-1200 mg elemental calcium daily for supplementation (taken in divided doses of ≤500-600 mg with meals) and 0.5-2 grams as needed for antacid use. 1, 2
Elemental Calcium Content
- Calcium carbonate contains 40% elemental calcium, the highest concentration among commonly available calcium salts 3, 2
- A 1000 mg calcium carbonate tablet provides 400 mg of elemental calcium 2
- This makes it the most cost-effective calcium supplement option 1, 2
Primary Indications
As a Calcium Supplement
Recommended total daily calcium intake:
- Adults under 50 years: 1000 mg elemental calcium daily 1
- Adults over 50 years: 1200 mg elemental calcium daily 1
- Maximum safe upper limit: 2500 mg daily from all sources 1
As an Antacid
- Used for symptomatic relief of heartburn and acid indigestion 1
- Typical antacid dosing ranges from 0.5-2 grams as needed 1
As a Phosphate Binder
- In chronic kidney disease (CKD) and end-stage renal disease (ESRD), calcium carbonate binds dietary phosphate 1
- Dosing: 3-6 grams daily in divided doses 1
Optimal Dosing Strategy
For maximum absorption efficiency:
- Take no more than 500-600 mg elemental calcium at one time (approximately 1250-1500 mg calcium carbonate) 1, 2
- Administer with meals - calcium carbonate requires gastric acid for optimal absorption 1, 4, 2
- Divide total daily dose into 2-3 administrations throughout the day with meals 4, 2
- A 4-times-daily regimen (with meals and at bedtime) results in substantially greater absorption than once-daily dosing 4
Critical Absorption Considerations
Calcium carbonate absorption is acid-dependent:
- Must be taken with food to ensure adequate gastric acid secretion 2, 5
- Patients on proton pump inhibitors or H2-blockers should use calcium citrate instead, as it does not require gastric acid for absorption 2, 5
- Patients with achlorhydria should also receive calcium citrate rather than calcium carbonate 2
Special Population Warnings
Chronic Kidney Disease Patients - CRITICAL SAFETY LIMITS
Maximum total calcium intake in CKD must not exceed 2.0 g/day (including dietary sources): 6
- CKD Stage 3: 1.5-2.0 g/day total 6
- CKD Stages 4-5 (non-dialysis): 1.5-1.8 g/day total 6
- Dialysis patients: maximum 2.0 g/day total 6
The 2018 KDIGO guidelines recommend restricting calcium-based phosphate binders due to increased risk of vascular calcification 6
Patients at Risk for Nephrolithiasis
- Increasing dietary calcium from food is associated with lower kidney stone risk compared to calcium supplements 1
- Measurement of urinary calcium excretion is prudent in patients with history of calcium kidney stones 1
Patients on Thiazide Diuretics
- At increased risk for milk-alkali syndrome (hypercalcemia and metabolic alkalosis) 7
- Require monitoring for alkalosis and hypercalcemia when using calcium supplements 7
Common Pitfalls to Avoid
- Do not assume "over-the-counter = safe" - account for all calcium sources including dietary intake, supplements, and fortified foods 6
- Avoid single large doses - absorption efficiency decreases significantly with doses >500-600 mg elemental calcium 2
- Do not take on an empty stomach - absorption is substantially reduced without food-stimulated gastric acid 4, 2
- Do not exceed 2500 mg total daily calcium except under medical supervision, as mineral deficiencies may develop 7
- In CKD patients, never exceed 2.0 g/day total calcium from all sources 6
Adverse Effects
- Most common: gastrointestinal complaints including constipation, bloating, and gas 2
- Renal calculi have not been consistently associated with calcium supplementation in most studies 2
- Calcium intakes >1500 mg/day have been associated with increased risk of advanced and fatal prostate cancer 2