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

Department of Family Medicine (T.D.T.), Mayo Clinic, Rochester, Minnesota 55905; Department of Family Medicine (M.O.O.), Jos University Teaching Hospital, Jos 930001, Nigeria; Division of Nutritional Sciences (K.O.O.), Cornell University, Ithaca, New York 14853; and U.S. Department of Agriculture/Agricultural Research Service Children’s Nutrition Research Center (S.A.A.), Department of Pediatrics, Baylor College of Medicine Houston, Texas 77030

Address all correspondence and requests for reprints to: Tom D. Thacher, M.D., Department of Family Medicine, Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905. E-mail: thacher.thomas{at}mayo.edu.

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 D₃ (n = 8) or vitamin D₂ (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 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.