NKF 2009: Vitamin D Supplementation Benefits Dialysis Patients

Bob Roehr

April 01, 2009

April 1, 2009 (Nashville, Tennessee) – Over-the-counter vitamin D supplementation improves serum 25-hydroxyvitamin D levels in patients with chronic kidney disease undergoing dialysis, without raising serum calcium or phosphorus levels, according to poster presented here at the National Kidney Foundation 2009 Spring Clinical Meetings.

Previous studies have shown cholecalciferol to be more effective than ergocalciferol in raising serum levels of vitamin D in predialysis patients; this was the first published study to look at the issue in patients on dialysis.

A total of 84 patients at the South Plaines Kidney Disease Center, in Lubbock, Texas, were screened for serum 25-hydroxyvitamin D levels, and 68 patients (81%) were found to have levels less than 30 ng/mL. National Kidney Foundation Disease Outcomes Quality Initiative guidelines call for supplementation below that level, lead author and dietician Louise Clement, MS, told Medscape Nephrology.

At baseline, "a subset of patients (19%) had vitamin D levels in the normal range. About half of them were taking a multiple vitamins on their own," whereas others had regular sun exposure in their lives.

The patients with vitamin D deficiency received an over-the-counter once-daily dose of 1000 IU cholecalciferol for 20 weeks. Ms. Clement said pill count was not always a reliable measure of compliance because serum levels of vitamin D did not support all patient claims that they were regularly taking the supplement.

In the group identified as compliant, serum levels of vitamin D increased significantly from baseline (16.2 ± 6.5 to 51.4 ± 14.4 ng/mL; P < 0001). Ms. Clement said patients took an estimated 87% of their pills.

Serum calcium levels were slightly but significantly lower after supplementation (9.3  0.5 to 9.1  0.6; P < .0007), whereas mean serum phosphorus levels were not significantly different (P < .365).

Ms. Clement said there is significant controversy about what constitutes healthy minimal and optimal levels of vitamin D. Recent studies suggest that serum levels should be higher than current guidelines, and the Institute of Medicine is reviewing the issue.

Studies in healthy patients have provided supplementation up to 10,000 IU a day with no observed adverse effects. However, it is not known if that also applies to patients with chronic kidney disease, or if it varies depending on degree of renal impairment.

"One of my patients reached a serum vitamin D level of 90 [ng/mL], and I began to worry about the possibility of skin calcification," Ms. Clement said. She advised the patient to reduce the supplementation to every other day.

Baseline samples were collected in November, when serum levels of vitamin D from sun exposure are still near their peak in Texas, and the end samples were gathered in May, when serum levels are likely to have not recovered completely from their winter nadirs. Thus, it is unlikely that sun exposure contributed significantly to the increase in serum levels of vitamin D seen in the study, Ms. Clement said.

Leslie Spry, MD, a nephrologist from Lincoln, Nebraska, and spokesperson for the National Kidney Foundation, said the study was "very interesting" and found it useful to have this information in the dialysis population.

Dr. Spry said he has been using monthly observed administration of ergocalciferol in his dialysis patients for about 2 years. One concern he has with cholecalciferol is patient compliance with a daily self-administered supplement. The track record for dosing compliance with chronic diseases is spotty.

However, he has seen the emergence of resistance to ergocalciferol in about one fifth of his patients. "Rather than once a month, they sometimes require weekly administration of this stuff in order to achieve correction of serum levels" above 30 ng/mL. "I have had other people tell me that maybe cholecalciferol is better because it is the human form of vitamin D."

Although vitamin D supplementation is generally safe, Dr. Spry cautions that too high a level of use could contribute to the formation of kidney stones.

He also has seen 1 example of hypercalcemia, although the situation was highly unusual — a patient took ergocalciferol on a daily rather than a weekly basis for 3 months. Her vitamin D serum level surpassed 80 [ng/mL] and she developed the adverse effect. "We couldn't explain it until we got her vitamin D level back down."

The study was conducted as part of regular medical care and with volunteer assistance; it did not receive industry support. Ms. Clement and Dr. Spry have disclosed no relevant financial relationships.

National Kidney Foundation (NKF) 2009 Spring Clinical Meetings: Poster 209. Presented March 25–29, 2009.


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