Calcium Supplements

Medications that reduce stomach acid can interfere with absorption of calcium.

Claudia Wober, BSc(Pharm), BFA Drug and Poison Information Centre, Vancouver

Many people do not obtain enough calcium in their diet and need to take calcium supplements to ensure adequate intake and to build and maintain healthy bones. Calcium supplements are sold as various “salts” in which the amount of elemental calcium varies. For example, a 1250 mg tablet of calcium carbonate contains only 500 mg of elemental calcium. A person taking one such tablet each day might think they are meeting or exceeding their daily requirement for elemental calcium (1000 to 1500 mg/day). In fact, they would only be getting 500 mg of elemental calcium and, depending on their diet, may not be getting enough of this essential mineral. Always check the amount of elemental calcium in a product and consult your pharmacist if unsure.

The body can only absorb a portion of the calcium ingested at one time. For this reason it is better to take doses of up to 500 mg of calcium at different times of the day.

Calcium supplements are best taken with meals to ensure that the calcium is absorbed. Calcium carbonate must be exposed to acid in the stomach to dissolve. If not taken with food, which stimulates production of stomach acid, the calcium may not dissolve and won’t be absorbed from the gut. Undissolved calcium carbonate may cause bloating and constipation. Talk to your pharmacist if you take calcium tablets and experience these symptoms.

Calcium citrate does not need stomach acid to dissolve and may be taken without food. Calcium citrate is generally more expensive than calcium carbonate and larger quantities of calcium citrate must be taken to get the same amount of elemental calcium (1000 mg of calcium citrate contains 211 mg of elemental calcium).

Medications that reduce stomach acid can interfere with absorption of calcium. These include medicines used for stomach ulcers or gastroesophageal reflux (e.g., omeprazole, ranitidine and many others). Talk to your pharmacist if you take a stomach medicine and need to take a calcium supplement.

Calcium can interfere with the effects of some medicines by preventing absorption of the drug. These include some, but not all, antibiotics (e.g., ciprofloxacin) and iron supplements. If your pharmacist knows that you take calcium supplements he or she can check to see if there is a problem and provide advice on how to manage the situation. It is important to check with your pharmacist before taking other medications and to always tell them about your nonprescription medicines or supplements.