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Vitamin D for Kidney Disease Unproven

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Updated: 4/21 12:08 pm

Dec. 17, 2007 -- Vitamin D compounds, routinely given to patients with chronic kidney disease to help preserve their bones, are not proven scientifically to help, according to a new report.

Researchers evaluated 76 published trials on vitamin D compounds, performing what is known as a meta-analysis, in which the results of several studies are combined.

Bottom line: "Despite many years of use, this is an intervention ... of unproven efficacy when it comes to achieving what really matters -- that is, a reduction in deaths, fractures, and cardiovascular events," says Giovanni Strippoli, MD, research coordinator at the Mario Negri Sud Consortium in Italy and a co-author of the study.

The Problem

In chronic kidney disease, caused by such conditions as high blood pressure and diabetes, the organs do not work properly and can eventually fail, leading to a need for dialysis.

Chronic kidney disease patients are often deficient in vitamin D, which helps maintain normal blood levels of calcium and phosphorous and helps promote calcium absorption, important for strong bones.

Diseased kidneys can't remove excess phosphorous found in foods as normal kidneys do. As phosphorous builds up, calcium in the blood drops. Then four small glands in the neck, called the parathyroid glands, become too active and too much calcium is removed from the bones, causing them to weaken and possibly fracture, according to the National Kidney Foundation.

When parathyroid hormone, as well as blood levels of phosphorous and calcium, builds up to excess, the risk of bone fractures, disability, and death increase.

To remedy the problem, doctors generally advise eating a low-phosphorous diet and taking one of a variety of medicines with a form of vitamin D and other components, either orally or injectables.

"Vitamin D compounds have been used for over 30 years and are very widespread," Suetonia Palmer, MBChB, a clinical research training fellow at the University of Otago, New Zealand, tells WebMD. "However, their effect on mortality and cardiovascular health remains unknown."

The Analysis: Vitamin D for Kidney Disease

Palmer, Strippoli and their colleagues searched medical databases from January 1966 through July 2007 to find published studies of vitamin D compounds for chronic kidney disease. They selected 76 that met their criteria for inclusion. In all, 3,667 participants were in these 76 studies.

When they pooled the results and analyzed them, the researchers found that the vitamin D compounds did not consistently reduce the parathyroid hormone levels or reduce the risk of death, bone pain, blood vessel calcification, or other problems.

When they compared the established vitamin D sterols with placebo, the vitamin D treatments were associated with a 2.3 times higher risk of high calcium levels and a nearly two times higher risk of high phosphate in the blood. And the treatment didn't consistently reduce the parathyroid hormone levels.

Newer types of vitamin D treatment did not perform better.

The analysis is published in the Annals of Internal Medicine.

Another Perspective

In an editorial accompanying the analysis, Marcello Tonelli, MD, associate professor of medicine at the University of Alberta in Edmonton, Canada, writes: "Palmer and colleagues' findings should serve as yet another warning to the nephrology community that we do not have good evidence to defend many of our common practices."

"We need to do more research," Tonelli tells WebMD. "To figure out the best role for these medicines, a large trial or trials are needed, probably funded by a U.S. government agency such as the National Institutes of Health."

He reports as a potential conflict of interest that he receives funding from the Centre for D-Receptor Activation Research to examine vitamin D status in remote-dwelling patients on dialysis.

Message for Kidney Disease Patients

Strippoli and Palmer, too, call for more research in the area to prove the treatments work.

Meanwhile, those with chronic kidney disease should follow their doctors' advice, Strippoli says. Until more is known, patients should closely follow, in particular, advice about preventive measures suggested by their doctors, including dietary advice and recommendations to undergo longer dialysis times.

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