3.11: Calculating the Amount of a Mineral in a Supplement
- Page ID
- 55710
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Mineral supplements like calcium or iron are ingested in combination with other elements because they don’t occur in nature as calcium or iron alone. Calcium carbonate and calcium gluconate are common calcium supplements. Some people taking them don’t realize that a 500 mg tablet of calcium carbonate has four times as much calcium as a 500 mg tablet of calcium gluconate.
To calculate the amount of calcium in a calcium supplement, one must know the:
- atoms that make up the supplement
- atomic weights of those atoms
- how many of each atom in the molecule (molecular formula)
The molecular formula of calcium carbonate is CaCO3, meaning it has one atom of calcium (Ca), one atom of carbon (C), and three atoms of oxygen (O). The atomic weight is 40 for calcium atom, 12 for carbon, and 16 for oxygen (refer to Appendix A-3 for atomic weights).
The molecular weight of calcium carbonate is the total of the atomic weights of all its atoms: 40+12+16+16+16 = 100. Calcium accounts for 40 of that 100 (40%), so a 500 mg tablet of calcium carbonate contains 200 mg of calcium (40/100 x 500 mg = 200 mg).
In comparison, the molecular formula for calcium gluconate is C12H22CaO14. The amount of calcium in a 500 mg tablet of calcium gluconate is calculated using the same method:
Calcium accounts for 40 of the total of 430 (9%), so a 500 mg tablet of calcium gluconate has only 47 mg of calcium (40/430 X 500 mg = 47 mg). This means that if you take 800 mg of calcium as a dietary supplement, you need to take seventeen 500 mg tablets of calcium gluconate—or four 500 mg tablets of calcium carbonate. Other calcium supplements include calcium lactate (13% calcium) and calcium citrate (21% calcium).