Calcium Supplements Linked To Increased Risk of Kidney Stones Interview with:
Christopher Loftus M.D. candidate
Cleveland Clinic Lerner College of Medicine

Medical Research: What is the background for this study? What are the main findings?

Response: Most kidney stones are made, at least partially, of calcium composite. In a prospective study of nurses in the post-menopausal age, it was found that diets that contained high amounts of calcium were beneficial in preventing kidney stones in this population. In the gut, calcium can bind to oxalate which prevents it from being absorbed into the body and decreases the concentration of calcium in the urine. However there has been debate as to whether supplemental calcium (calcium pills) has the same beneficial effects as calcium in the diet. Supplemental calcium enters the gut in large quantities all at once so it may enter the blood stream in higher concentrations over smaller amounts of time. By the same token, vitamin D plays a role in the management and balance of calcium in the body and could potentially have an effect on stone formation as well.  It has also been debated whether vitamin D supplementation has major effect on patients who are known to be stone formers.  So we reviewed CT scans of patients and 24 hour urine collections (both male and female of adult age) who were known to have kidney stones and measured the growth of stones over a period of time.

Our main findings were that supplementary calcium increased the rate of stone formation in these patients. We also found that vitamin D had a protective effect and patients taking only vitamin D had a slower rate of stone progression.

Medical Research: What should clinicians and patients take away from your report?

Response: Calcium can enter the body in many forms but dietary calcium is likely used by the body differently than supplemental calcium. Though appropriate amounts of dietary calcium especially in foods like dairy products and green leafy vegetables are protective against kidney stones, supplemental calcium in pills like vitamins may increase the risk for stones. We are not advocating that calcium supplementation is necessarily harmful, as it is very beneficial for diseases like osteoporosis and others. But these findings suggest that patients at risk for kidney stones who are also taking calcium should have meaningful discussion with their doctors and weigh any potential added risk of forming stones.

Medical Research: What recommendations do you have for future research as a result of this study?

Response: We will need to conduct prospective, randomized trials in large groups of patients to see whether these results can be replicated in future studies. Retrospective studies such as ours may have potential biases so more studies will be needed to confirm our results.


Christopher Loftus is scheduled to present his findings November 2015 at the American Society of Nephrology’s annual meeting in San Diego.

SOURCES: Christopher Loftus, M.D. candidate, Cleveland Clinic Lerner College of Medicine, Ohio; Mathew Sorensen, M.D., assistant professor, urology, University of Washington, Seattle; news release, Oct. 13, 2015, American Society of Nephrology meeting, San Diego

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Christopher Loftus M.D. candidate (2015). Calcium Supplements Linked To Increased Risk of Kidney Stones