Health answers: Can calcium supplements cause kidney stones?

Q. Can calcium supplements cause kidney stones?

A. Calcium supplements have been touted as a way to maintain bone health, particularly for postmenopausal women at risk of developing osteoporosis. But a potential downside has emerged. The incidence of kidney stones — hard masses of crystals that form in the urinary tract and can cause pain as they pass — has jumped in recent decades. Much of that rise can be explained by obesity and diabetes, but there’s evidence for a link between calcium supplements and kidney stones. A Women’s Health Initiative randomized clinical trial of calcium and vitamin D supplements found a 17 percent higher incidence of kidney stones in postmenopausal women who took supplements over those who didn’t.

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Murray Favus, director of University of Chicago Medicine’s bone program, says that the body may process the calcium in supplements differently than calcium in foods. A significant amount of calcium from supplements is excreted in the urine, which might set the stage for kidney stones (the majority of which contain calcium). Paradoxically, he says, “people who eat a low-calcium diet are much more likely to have kidney stones.” He believes the best approach is to aim for a diet rich in calcium from foods, rather than supplements.

In addition, two recent studies have found evidence that calcium supplements may increase heart attack risk. Favus says that the evidence for the link is not yet clear, but in the meantime, he’s advising patients to hold off on supplements until the risks are sorted out.