Understanding Elemental Calcium Content in Calcium Supplements
No, you have a critical misunderstanding: A Caltrate 600 mg tablet contains 600 mg of elemental calcium, not 600 mg of calcium carbonate. The tablet actually contains approximately 1,500 mg of calcium carbonate, which provides 600 mg of elemental calcium 1.
The Key Concept: Calcium Carbonate vs. Elemental Calcium
Calcium carbonate is only 40% elemental calcium by weight 2. This is the fundamental principle you need to understand:
- Calcium carbonate = the total compound weight (includes calcium + carbonate)
- Elemental calcium = the actual calcium content available for absorption
The Math
When you see calcium carbonate supplements:
- A 500 mg calcium carbonate tablet contains 200 mg elemental calcium (500 mg × 40% = 200 mg)
- A 1,500 mg calcium carbonate tablet contains 600 mg elemental calcium (1,500 mg × 40% = 600 mg)
Caltrate 600 Labeling
The FDA drug label for Caltrate clearly states: "Calcium (as calcium carbonate) 600 mg" 1. This means:
- The product delivers 600 mg of elemental calcium
- This comes from approximately 1,500 mg of calcium carbonate
- The "600" in the product name refers to elemental calcium, not the calcium carbonate dose
Clinical Relevance
This distinction matters because:
- Dosing recommendations are always in elemental calcium 2
- Women >50 years need 1,200 mg/day of elemental calcium
- Men >70 years need 1,200 mg/day of elemental calcium
- Upper limits (2,000-2,500 mg/day) refer to elemental calcium
Common Pitfall
The most common error is confusing the calcium carbonate dose with elemental calcium content. Always calculate or check the elemental calcium amount when prescribing or recommending supplements. Different calcium salts have different percentages of elemental calcium:
- Calcium carbonate: 40% elemental calcium 2
- Calcium citrate: 21% elemental calcium 2
- Calcium gluconate: 9% elemental calcium 2
- Calcium lactate: 13% elemental calcium 2
When counseling patients, always specify elemental calcium amounts to avoid overdosing or underdosing.