The effect of vitamin D2 and vitamin D3 on intestinal calcium absorption in Nigerian children with rickets

Abstract

Context: Children with calcium-deficiency rickets have high 1,25-dihydroxyvitamin D values. Objective: The objective of the study was to determine whether vitamin D increased calcium absorption. Design: This was an experimental study. Setting: The study was conducted at a teaching hospital. Participants: Participants included 17 children with nutritional rickets. Intervention: The participants were randomized to 1.25mg oral vitamin D 3 (n=8) or vitamin D2 (n=9). Main Outcome Measure: Fractional calcium absorption 3 da after vitamin D administration was measured. Results:Mean base line 25-hydroxyvitamin D concentrations were 20 ng/ml (range 5-31 ng/ml). The increase in 25-hydroxyvitamin D was equivalent after vitamin D3 (29±10 ng/ml) or vitamin D2 (29± 17 ng/ml). Mean 1,25-dihydroxyvitamin D values increased from 143±76 pg/ml to 243±102 pg/ml (P = 0.001), and the increase in 1,25-dihydroxyvitamin D did not differ between vitamin D2 and vitamin D3 (107 ± 110 and 91 ± 102 ng/ml, respectively). The increment in 1,25-dihydroxyvitamin D was explained almost entirely by the baseline 25-hydroxyvitamin D concentration (r2=0.72; P< 0.001). Mean fractional calcium absorption did not differ before (52.6 ± 21.4%) or after (53.2 ± 23.5%) vitamin D, and effects of vitamin D2 and vitamin D3 on calcium absorption were not significantly different. Fractional calcium absorption was not closely related to concentrations of 25-hydroxyvitamin D (r=0.01, P=0.93) or 1,25-dihydroxyvitamin D (r=0.21, P=0.24). The effect of vitamin D on calcium absorption did not vary with baseline 25-hydroxyvitamin D values or with the absolute increase in 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D values. Conclusions: Despite similar increases in 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D with vitamin D2 or vitamin D3, fractional calcium absorption did not increase, indicating that rickets in Nigerian children is not primarily due to vitamin D-deficient calcium malabsorption. Copyright © 2009 by The Endocrine Society.