Choosing a calcium supplement

What you should know about taking calcium to boost your nutrients

Experts agree that the ideal way to get the nutrients you need to stay healthy is from food. But when it comes to taking calcium, some people may not find it practical or possible to meet the recommended daily intake (RDI) from diet alone. For adults, the RDI is 1,000 milligrams (mg) daily, which rises to 1,200 mg per day for women over age 50 and men over age 70.

If your doctor advises you to take a calcium supplement, how do you choose among the dizzying array of available choices, which include pills, chewable tablets, flavored chews, and liquids? The following information may help you decide.

What form of calcium?

The calcium in supplements is found in combination with another substance, typically carbonate or citrate. Each has benefits and downsides. Calcium carbonate supplements tends to be the best value, because they contain the highest amount of elemental calcium (about 40% by weight). Because calcium carbonate requires stomach acid for absorption, it's best to take this product with food. Most people tolerate calcium carbonate well, but some people complain of mild constipation or feeling bloated. Some well-known calcium carbonate products include Caltrate, Viactiv Calcium Chews, Os-Cal, and Tums.

Calcium citrate supplements are absorbed more easily than calcium carbonate. They can be taken on an empty stomach and are more readily absorbed by people who take acid-reducing heartburn medications. But because calcium citrate is only 21% calcium, you may need to take more tablets to get your daily requirement. Calcium citrate products include Citracal and GNC Calcimate Plus 800.

How much calcium per serving?

Reading the labels with an eye toward cost and convenience may help you sift through your options. Check the serving size and the "% Daily Value" for calcium and multiply the percentage by 10 to find out how much elemental calcium the product contains. For example, if the label says a serving of the product contains 40% of the Daily Value, it has 400 mg of elemental calcium.

While products that yield a high amount of calcium may seem to be the best bet at first blush, they may not serve you best. Because your body has difficulty absorbing more than 500 mg of calcium at a time, more of the mineral may go to waste. So, while you may think that you've met your daily requirements by taking that 1,000-mg calcium pill, you may actually be only halfway to your target. Calculate your cost per serving based on how many tablets or chews the package contains, and consider whether you might find it inconvenient to take several tablets a day.  

Here are some final tips for choosing and taking calcium supplements as found in the Harvard Special Health Report Osteoporosis: A guide to prevention and treatment:

• Avoid products made from unrefined oyster shell, bone meal, dolomite, or coral, as they may contain lead or other toxic metals.

• Don't exceed the daily dose recommended by the manufacturer—doing so increases the risk for side effects.

• If you take iron or zinc supplements, tetracycline antibiotics, or levothyroxine (used to treat hypothyroidism), take them several hours before or after takingcalcium to avoid potential negative interactions.

• Make sure you're also getting enough vitamin D, which helps your body absorb calcium. If you aren't getting enough from sunlight, your diet, or your multivitamin, you may want to choose a calcium supplement that contains vitamin D.

– By Julie Corliss
Executive Editor, Harvard Heart Letter