Vitamin D, Calcium May Increase Risk of Kidney Stones

HOUSTONTaking calcium and vitamin D supplements could increase the risk of kidney stones suggested a new study presented at The Endocrine Societys 94th Annual Meeting in Houston. Researchers reported that the supplements increase calcium levels in the blood and urine, which could lead to kidney stones. However, no incidents of kidney stones were reported during this one-year study.

Researchers, studied 163 healthy, postmenopausal women between the ages of 57 and 85 years. All participants were randomly assigned to receive a vitamin D supplement of 400, 800, 1,600, 2,400, 3,200, 4,000 or 4,800 IU/d, or placebo. Then, their calcium intake was increased from an initial intake of 691 to 1,200 to 1,400 mg/d. Investigators measured blood and urinary calcium levels at the beginning of the study, and then every three months for one year.

They found approximately 48 participants, or 33 percent, developed high urinary levels of calcium at some time in the study. These participants had 88 episodes of high urinary calcium. Additionally, about 10 percent of study subjects developed high blood levels of calcium. This translates into 25 episodes among 16 participants. In both cases, the increases were unrelated to the dosage of vitamin D.

Principal investigator J. Christopher Gallagher, M.D., professor and director of the Bone Metabolism Unit at Creighton University Medical Center in Omaha, NE, said this study helps show people should not exceed the guidelines suggested by the Institute of Medicine (IOM), which are 800 IU/d of vitamin D, and 800 to 1,200 mg/d of calcium.

 Because of the unpredictable response, it is not clear whether it is the extra calcium, the vitamin D or both together that cause these problems," Gallagher said. However, it is possible that long-term use of supplements causes hypercalciuria and hypercalcemia, and this can contribute to kidney stones. For these reasons, it is important to monitor blood and urine calcium levels in people who take these supplements on a long-term basis. This is rarely done in clinical practice."

Cara Welch, vice president of scientific and regulatory affairs , the Natural Products Association (NPA), said the increased risk of kidney stones when supplementing with calcium and vitamin D is not a new development, but being deficient in these nutrients can pose a serious danger.  "Manufacturers should be assured that vitamin D and calcium supplements will still be necessary for consumers, especially because we know several populations are at risk for being deficient in calcium and/or vitamin D, and consumers do not necessarily get the recommended amounts of these nutrients from their diet. As always, the Natural Products Association recommends consulting with a health care provider before incorporating dietary supplements into ones health regimen."

Douglas "Duffy" MacKay, N.D., vice president, scientific and regulatory affairs, the Council for Responsible Nutrition (CRN), noted this study does not change to the idea that people should achieve the right amount of calcium and vitamin D through their diets and supplementation. Problems can arise if people get too much of these nutrients, especially calcium, MacKay said. " If you look at the totality of evidence in this area, it appears the risks occurs when you start to reach 2,000 mg/d of calcium."

MacKay said a control group could have helped reduce the unpredictable aspect of the study. "Without a control group to compare to, this could not be related to the supplementation at all. An 'unpredictable response' means that it was not dose dependent and was random, so the changes in the blood levels of calcium and D could have been chance or individual metabolic/kidney issues with subjects. Without a control group to compare to, you cant rule this out or say it is form the supplements."

MacKay said this study adds to the mixed evidence of calcium and vitamin D's effects on kidney stones, but noted this study hasn't been peer reviewed or published yet. "This is just data a scientist is bringing to a conference. I don't think we'll see the real data unless you go the meeting for a long time because they have to submit this to publication." Particularly, MacKay said we don't yet know what the  baseline dietary calcium intake was and at which dosing level the stones start to occur.

Further, "I think they overstate their conclusion," MacKay said. "If you have an association with urinary calcium, to call out a straight link to kidney stones is overreaching."

However, MacKay praised the researchers' conclusion that clinicians should consider urine and blood tests. "That's not a bad idea. Getting people in the target range for calcium intake is a good thing."

And supplementing with these two nutrients have shown great health benefits, including a recent study on the combination of vitamin D and calcium found the supplements were linked to lower mortality rates in elderly people.