Calcium Carbonate
Also known as: CaCO3, oyster shell calcium, precipitated calcium carbonate, limestone calcium
The most concentrated and least expensive common calcium salt, supplying about 40% elemental calcium by weight. It is the default form in bone formulas, multivitamins, and chewable antacid-style tablets because a full serving fits in fewer tablets than any other form. Absorption depends on stomach acid, so it is usually taken with meals. It is also widely used as a tablet excipient, which is worth remembering when totaling calcium on a label.
Research summary
Provides calcium for bone mineralization, muscle contraction, and nerve signaling; carbonate dissolves in gastric acid before the calcium ion is absorbed.
Dosage
Daily amounts, elemental (40% of the compound is the element).
| Lowest studied | Typical range | Highest studied | Upper limit |
|---|---|---|---|
| 200 mg | 250–600 mg | 1,200 mg | 2,000 mg |
NIH ODS — UL is 2,500 mg/day for adults 19–50 and 2,000 mg/day for adults 51+; the app uses the lower adult value (total intake from food plus supplements)
Doses are elemental calcium. Take with food, since carbonate needs an acidic stomach to dissolve. Fractional absorption falls as the single dose rises, so amounts above about 500 mg elemental are commonly split across the day. Large trials have supplemented 1,000–1,200 mg/day; the adult UL of 2,000–2,500 mg counts food as well as supplements. Constipation and bloating are the usual complaints at higher doses.
Source material: mined limestone or precipitated (synthetic) calcium carbonate; oyster shell in some products
As supplied: ≈ 40% Ca; 1,000 mg elemental ≈ 2,500 mg compound
Forms of Calcium
| Form | Typical dose | Element % | Formats | Price |
|---|---|---|---|---|
| Calcium Carbonate | 250–600 mg | 40% | Capsule, Powder, Tablet, Gummy, Liquid | low |
| Calcium Citrate | 200–500 mg | 21% | Capsule, Powder, Tablet, Gummy, Liquid | low |
| Calcium Citrate Malate | 250–500 mg | 23% | Capsule, Powder, Tablet, Liquid | mid |
| Calcium (Microcrystalline Hydroxyapatite, MCHC) | 250–700 mg | 24% | Capsule, Powder, Tablet | high |
Format suitability
- Capsule
- Powder
- Tablet
- Softgel
- Gummy
- Liquid
Dense and compressible, so tablets are the natural fit. 500 mg elemental is 1,250 mg of powder, which is about two size-00 capsules. Chalky taste in gummies and liquids; chewables usually flavor around it.
Formulation notes
Separate from iron, zinc, and thyroid hormone by a few hours because calcium lowers their absorption. Vitamin D and vitamin K2 are common formulation partners. Calcium can also cut absorption of some antibiotics.
- Has an upper limit
- Possible Prop 65 warning
Sources
Related ingredients
Calcium Citrate
MineralA calcium salt of citric acid that does not rely on stomach acid to dissolve, so it can be taken with or without food and is often chosen for older adults and people on acid-reducing medication.
Typical: 200–500 mg
Vitamin D3 (Cholecalciferol)
VitaminThe form of vitamin D the body makes from sunlight and the most effective supplemental form for raising blood levels.
Typical: 1,000–2,000 IU
Folic Acid
VitaminFolic acid is the fully oxidized, synthetic form of folate used in food fortification and most supplements.
Typical: 400–800 mcg
Magnesium Oxide
MineralThe most concentrated magnesium source at about 60% elemental magnesium, which is why it dominates in multivitamins and small tablets.
Typical: 200–350 mg
Iron Bisglycinate
MineralFerrous iron chelated with two glycine molecules, the form most prenatal and gentle-iron products now use.
Typical: 18–30 mg