Extra vitamine D voor dialysepatiënten*
Uit een studie onder 84 dialysepatiënten blijkt dat supplementering met vitamine D duidelijk zorgt voor betere bloedwaarden vitamine D en voor nauwelijks veranderde calcium- en fosforwaarden. 81% van de patiënten bleken bij aanvang van de studie bloedwaarden vitamine D te hebben die lager waren als geadviseerd (>30ng/ml), gemiddeld 16 ng/ml. Deze patiënten kregen 20 weken lang dagelijks 25 mcg extra vitamine D. Na 20 weken bleken de bloedwaarden vitamine D goed te zijn en wel gemiddeld 51 ng/ml.
Vitamin D Supplementation Benefits Dialysis Patients
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 a 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 examine the issue in patients receiving 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 vitamin on their own," while 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. She said pill count was not always a reliable measure of compliance as 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), while 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 U a day with no observed adverse effects. However, it is not known whether 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, 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 Lincoln, Nebraska, nephrologist and spokesman for the National Kidney Foundation, found the study to be "very interesting" and thought it was 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 now. 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 a 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 may contribute to the formation of kidney stones.
He also has seen one example of hypercalcemia, though 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 the 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 2009 Spring Clinical Meetings: Abstract 209.
Pearls for Practice
· Of the patients with chronic kidney disease, 81% have 25-hydroxyvitamin D levels below 30 ng/mL and require vitamin D supplementation, with only 19% of patients having levels in the normal range.
· Supplementation of vitamin D–deficient patients with chronic kidney disease with 1000 U daily of cholecalciferol increases 25-hydroxyvitamin D levels from 16.2 to 51.4 ng/mL in those who are 87% adherent, with slight but significant lowering of calcium and no change in phosphorus
levels. (Mei
2009)
