Calcium

What it is

Calcium is an essential mineral and the most abundant mineral in the body, where the vast majority is stored in bones and teeth to provide structure. The small amount circulating in the blood supports muscle contraction, nerve signaling, blood vessel function, and hormone secretion. Supplements typically supply it as calcium carbonate (40% elemental, best absorbed with food) or calcium citrate (21% elemental, absorbed with or without stomach acid).

Benefits

Adequate calcium intake supports bone mineral density and helps reduce fracture risk, especially in older adults and postmenopausal women. The Recommended Dietary Allowance is 1,000 mg/day for most adults, rising to 1,200 mg/day for women over 50 and everyone over 70, counting food plus supplements.

When to take it

Take calcium carbonate with food for best absorption; calcium citrate can be taken any time. Split doses so no more than about 500 mg of elemental calcium is taken at once, and separate it by several hours from thyroid medication, iron, and certain antibiotics.

Side effects

Supplemental calcium commonly causes gas, bloating, and constipation (more with carbonate); the Tolerable Upper Intake Level is 2,500 mg/day for adults 19-50 and 2,000 mg/day after 50, above which hypercalcemia and kidney-stone risk rise. Some meta-analyses have linked high-dose supplements (not dietary calcium) to a possible increase in cardiovascular risk in postmenopausal women, though the evidence is conflicting; calcium can also reduce absorption of levothyroxine, quinolone and tetracycline antibiotics, and raises hypercalcemia risk with lithium.

Sources

• Calcium - Health Professional Fact Sheet, NIH Office of Dietary Supplements

Products containing Calcium

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