Amount of calcium
Elemental calcium is key because it’s the actual amount of calcium in the supplement. It’s what your body absorbs for bone growth and other health benefits. The Supplement Facts label on calcium supplements is helpful in determining how much calcium is in one serving. As an example, calcium carbonate is 40 percent elemental calcium, so 1,250 milligrams (mg) of calcium carbonate contains 500 mg of elemental calcium. Be sure to note the serving size (number of tablets) when determining how much calcium is in one serving.
Tolerability
Calcium supplements cause few, if any, side effects. But side effects can sometimes occur, including gas, constipation and bloating. In general, calcium carbonate is the most constipating. You may need to try a few different brands or types of calcium supplements to find one that you tolerate the best.
What prescriptions you take
Calcium supplements can interact with many different prescription medications, including blood pressure medications, synthetic thyroid hormones, bisphosphonates, antibiotics and calcium channel blockers. Depending on your medications, you may need to take the supplement with your meals or between meals. Ask your doctor or pharmacist about possible interactions and which type of calcium supplement would work for you.
Quality and cost
Manufacturers are responsible for ensuring that supplements are safe and claims are truthful. Some companies have their products independently tested by U.S. Pharmacopeial Convention (USP), ConsumerLabs.com (CL) or NSF International (NSF). Supplements that bear the USP, CL or NSF abbreviation meet voluntary industry standards for quality, purity, potency, and tablet disintegration or dissolution. Different types of calcium supplements have different costs. Comparison shop if cost is a factor for you.
Supplement form
Calcium supplements are available in a variety of forms, including tablets, capsules, chews, liquids and powders. If you have trouble swallowing pills, you may want a chewable or liquid calcium supplement.
Absorbability
Your body must be able to absorb the calcium for it to be effective. All varieties of calcium supplements are better absorbed when taken in small doses (500 mg or less) at mealtimes. Calcium citrate is absorbed equally well when taken with or without food and is a form recommended for individuals with low stomach acid (more common in people over 50 or taking acid blockers), inflammatory bowel disease or absorption disorders.