Vitamin D Deficiency Prevalent in Children With Chronic Kidney Disease

Fran Lowry

March 05, 2009

March 5, 2009 — There is a high and growing prevalence of vitamin D deficiency in children with chronic kidney disease, adding to their already high risk for impaired bone development, according to a study reported in the March issue of Pediatrics.

"Vitamin D deficiency in children adversely affects bone development by reducing mineralization. Children with chronic kidney disease are at risk for altered bone development from renal osteodystrophy and concomitant vitamin D deficiency," write Farah N. Ali, MD, from the Feinberg School of Medicine, Northwestern University, Chicago, Illinois, and colleagues. "The pediatric Kidney Disease Outcomes Quality Initiative [KDOQI] guidelines suggest measuring serum 25-hydroxyvitamin D (25[OH]D) levels if serum parathyroid hormone levels are above the target range for chronic kidney disease stages 2 and beyond, but the magnitude of vitamin D deficiency in children with chronic kidney disease is not well studied."

The goals of this study were to determine the extent of vitamin D deficiency in these children and whether the prevalence of this deficiency changed over time. The study also examined seasonal and ethnic differences in 25(OH)D levels.

Levels of 25[OH]D in 1074 ambulatory pediatric patients with chronic kidney disease stages 1 through 5 were measured once during a 10-year period from 1987 to 1996. Of this number, 403 patients (38%) had repeat measures during the decade.

The study also measured 25(OH)D levels in a random sample of 88 additional patients during 2005 to 2006.

"We chose to evaluate a cohort over a past decade (1987 to 1996), before KDOQI and the routine use of vitamin D supplementation, as well as a contemporary population (2005 to 2006) that followed the publication of KDOQI guidelines," the study authors write

The prevalence of vitamin D deficiency, defined as a 25(OH)D level lower than 15 ng/mL, ranged from 20% to 75% in the decade studied. In addition, an increasing prevalence of 25(OH)D levels lower than 15 ng/mL was noted from the beginning to the end of the decade (P < .001).

Seasonal variation in 25 (OH)D levels was also noted, with summer–fall values greater than values in winter–spring (P < .001). Analyzing only 1 measurement per patient, the patients who had their 25[OH]D levels tested in the summer–fall time period (from July through December) had significantly higher levels of vitamin D than those who had their levels of 25(OH)D tested in the winter–spring time period (from January through June; P < .05).

Analysis of the contemporary 2005 to 2006 data found a mean 25(OH)D level of 21.8 ng/mL and a median level of 17.7 ng/mL, "quite similar to those in the decade study," the study authors write.

The prevalence of deficiency in this contemporary study group was 39%, and the majority of the patients (72%) had levels of 25[OH]D lower than 32 ng/mL.

Analysis of the data according to ethnicity found that 13 black patients (68%) had 25(OH)D levels lower than 15 ng/mL, and 26 Hispanic patients of varying ancestry (90%) had 25[OH]D levels lower than 32 ng/mL. A total of 16 white patients (53%) were either vitamin D deficient or insufficient. The mean levels of 25(OH)D in black and Hispanic patients were 17 and 18 ng/mL, respectively, which were significantly lower than the mean level of 28 ng/mL found in white patients (P < .05).

The finding of more vitamin D deficiency in black and Hispanic children with chronic kidney disease validates previous knowledge that increased content of melanin does in fact decrease vitamin D production in the skin. "This is a problem that affects healthy children and adolescents, especially those with darkly pigmented skin, but [it] may be an extra threat to optimal bone health in such patients with underlying [chronic kidney disease] with altered vitamin D metabolism," the study authors write.

They also point out that the finding of increased prevalence of vitamin D deficiency during the decade studied "is noteworthy." Several factors may have contributed to this finding. These include possible referral bias, wherein physicians increasingly ordered 25(OH)D levels to be tested in patients whom they suspected to be at higher risk for vitamin D deficiency. The increasing prevalence of vitamin D deficiency could also be a result of changes in sunlight exposure during the decade, perhaps through increasing use of sunscreen or less time spent outdoors in the sun for this population of children.

A limitation of the study is the lack of dietary and supplement information overall, as well as the lack of data regarding racial background and underlying diagnoses in the population studied between 1987 and 1996.

The authors conclude, "Our data support the pediatric KDOQI guideline for the measurement of 12(OH)D levels in children with [chronic kidney disease], to reduce the effects of vitamin D deficiency as an important component of their renal osteodystrophy, now termed [chronic kidney disease]-mineral and bone disorder."

The authors have disclosed no relevant financial relationships.

Pediatrics. 2009;123:791–796.

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