Are certain calcium supplements absorbed better than others? —I.S.A., Baltimore

Yes, but the difference isn’t significant. All forms of calcium, such as calcium carbonate, calcium citrate, and tricalcium phosphate, are absorbed well enough to help you meet your daily requirement, especially when taken after a meal. And there’s no evidence that expensive varieties of calcium from coral, limestone, or oyster shells have any special benefit. So let cost or preference be your guide. Choose a supplement that carries the “USP Verified” seal, which indicates that it has been tested by the U.S. Pharmacopeia for purity.