Abstract
Children with calcium‐deficiency rickets may have increased vitamin D requirements and respond differently to vitamin D~2~ and vitamin D~3~. Our objective was to compare the metabolism of vitamins D~2~ and D~3~ in rachitic and control children. We administered an oral single dose of vitamin D~2~ or D~3~ of 1.25 mg to 49 Nigerian children—28 with active rickets and 21 healthy controls. The primary outcome measure was the incremental change in vitamin D metabolites. Baseline serum 25‐hydroxyvitamin D [25(OH)D] concentrations ranged from 7 to 24 and 15 to 34 ng/mL in rachitic and control children, respectively (p < .001), whereas baseline 1,25‐dihydroxyvitamin D [1,25(OH)~2~D] values (mean ± SD) were 224 ± 72 and 121 ± 34 pg/mL, respectively (p < .001), and baseline 24,25‐dihydroxyvitamin D [24,25(OH)~2~D] values were 1.13 ± 0.59 and 4.03 ± 1.33 ng/mL, respectively (p < .001). The peak increment in 25(OH)D was on day 3 and was similar with vitamins D~2~ and D~3~ in children with rickets (29 ± 17 and 25 ± 11 ng/mL, respectively) and in control children (33 ± 13 and 31 ± 16 ng/mL, respectively). 1,25(OH)~2~D rose significantly (p < .001) and similarly (p = .18) on day 3 by 166 ± 80 and 209 ± 83 pg/mL after vitamin D~2~ and D~3~ administration, respectively, in children with rickets. By contrast, control children had no significant increase in 1,25(OH)~2~D (19 ± 28 and 16 ± 38 pg/mL after vitamin D~2~ and D~3~ administration, respectively). We conclude that in the short term, vitamins D~2~ and D~3~ similarly increase serum 25(OH)D concentrations in rachitic and healthy children. A marked increase in 1,25(OH)~2~D in response to vitamin D distinguishes children with putative dietary calcium‐deficiency rickets from healthy children, consistent with increased vitamin D requirements in children with calcium‐deficiency rickets. © 2010 American Society for Bone and Mineral Research