The Effect of Vitamin D2 and Vitamin D3 on Intestinal Calcium Absorption in Nigerian Children with Rickets

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 1.25 mg oral vitamin D-3 (n = 8) or vitamin D-2 (n = 9). Main Outcome Measure: Fractional calcium absorption 3 da after vitamin D administration was measured. Results: Mean baseline 25-hydroxyvitamin D concentrations were 20 ng/ml (range 5-31 ng/ml). The increase in 25-hydroxyvitamin D was equivalent after vitamin D-3 (29 +/- 10 ng/ml) or vitamin D-2 (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 D-2 and vitamin D-3 (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 (r(2) = 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 D-2 and vitamin D-3 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 D-2 or vitamin D-3, fractional calcium absorption did not increase, indicating that rickets in Nigerian children is not primarily due to vitamin D-deficient calcium malabsorption. (J Clin Endocrinol Metab 94: 3314-3321, 2009)