Differences Between Calcium Citrate and Calcium Carbonate Supplements
Calcium citrate is preferable for patients with acid reflux, those taking acid-reducing medications, or those with absorption concerns, while calcium carbonate is more cost-effective with higher elemental calcium content (40% vs 21%) but requires stomach acid for proper absorption. 1, 2, 3
Elemental Calcium Content and Cost
- Calcium carbonate provides 40% elemental calcium by weight, making it the most cost-effective and commonly used calcium supplement 1, 3
- Calcium citrate provides only 21% elemental calcium, requiring larger or more frequent doses to achieve the same calcium intake 1, 3
- Other less common forms include calcium lactate (13% elemental calcium) and calcium gluconate (9% elemental calcium), which are rarely used for fracture prevention 1, 3
Absorption Differences
- Calcium carbonate requires gastric acidity for optimal absorption and must be taken with meals 1, 3
- Calcium citrate absorption is less dependent on gastric acidity, making it suitable for patients on acid-reducing medications (PPIs, H2 blockers) or those with achlorhydria 2, 3, 4
- For most people with normal stomach acid, both forms are adequately absorbed when taken appropriately (carbonate with food, citrate with or without food) 5
Gastrointestinal Effects
- Calcium carbonate is more likely to cause constipation, bloating, and reflux symptoms compared to calcium citrate 1, 2, 3
- Calcium citrate is recommended for patients with gastrointestinal issues, particularly those with GERD 2, 3
- Taking calcium supplements in divided doses (no more than 500 mg elemental calcium at once) helps minimize gastrointestinal side effects 1, 3
Special Populations
- For patients with GERD or those taking acid-reducing medications: calcium citrate is preferred 2, 4
- For patients who have undergone bariatric surgery: calcium citrate may be better absorbed 3, 6
- For patients at risk of kidney stones: calcium citrate may be preferred as it provides citrate, which can help prevent kidney stone formation 3, 6
- For patients with chronic kidney disease: calcium carbonate is often recommended 3
Dosing Recommendations
- For calcium carbonate: One or two 500-mg tablets taken two or three times daily with meals 1
- For calcium citrate: One or two 950-mg or 1000-mg tablets taken two or three times daily (can be taken with or without food) 1, 2
- Daily calcium intake should be 1000-1200 mg for adults, depending on age and sex 1, 3
- Upper intake levels should not exceed 2000-2500 mg per day 1, 3
Common Pitfalls to Avoid
- Failing to consider a patient's acid-reducing medication use when recommending calcium supplements 2, 4
- Taking calcium carbonate without food, which significantly reduces absorption 1, 3
- Taking more than 500 mg of elemental calcium at once, which reduces absorption efficiency 3, 4
- Overlooking the potential for calcium supplements to interact with certain medications (e.g., thyroid hormones, certain antibiotics) 3
- Assuming calcium citrate is always superior - for patients with normal stomach acid and no GI issues, calcium carbonate taken with meals is equally effective and more cost-efficient 5