Here are a few other things to keep in mind when choosing and taking a calcium supplement:

• Generally, calcium pills are better choices than multivitamins, which tend to have small amounts of elemental calcium.
   
• The National Osteoporosis Foundation recommends avoiding calcium products from unrefined oyster shell, bone meal, or dolomite that don’t have the United States Pharmacopeia (USP) symbol on them, since these products have tended to contain higher levels of lead, a toxic metal.
   
• Because calcium, iron, and zinc supplements interfere with each other, take them several hours apart.
   
• Delay consuming calcium (either from food or supplements) for two to four hours after taking tetracycline antibiotics, as calcium can decrease their effectiveness. Also, ask your doctor or pharmacist whether a supplement will interact with any prescription medications you’re taking.
   
• Don’t exceed the daily dose recommended by the manufacturer, since that increases the risk for side effects.
   
• Vitamin D helps your body absorb calcium, but it’s not necessary to take vitamin D and calcium at the same time. However, if you aren’t getting enough vitamin D from sunlight, your diet, or your multivitamin, you may want to choose a calcium supplement that contains this ingredient.
   
• To test how well the calcium in a supplement will be absorbed, put a tablet in 4 ounces of white vinegar and stir occasionally. If it doesn’t dissolve in 30 minutes, it’s not likely to dissolve in your stomach, which means it will simply pass through your body without being used.