Effect of a single oral dose of 600,000 IU of cholecalciferol on serum calciotropic hormones in young subjects with vitamin D deficiency: A prospective intervention study

Context: Effects of vitamin D repletion in young people with low vitamin D status have not been investigated so far. Objective: We evaluated the effect of a single massive dose of cholecalciferol on calcium metabolism at 3, 15, and 30 d, compared to baseline. Design and Setting: We conducted a prospective intervention study in an ambulatory care setting. Participants: Forty-eight young subjects with vitamin D deficiency participated in the study. Intervention: A single oral dose of 600,000 IU of cholecalciferol was administered to each subject. Main Outcome Measures: We evaluated serum changes of 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D, calcium, and PTH induced by a single load of cholecalciferol. Results: The 25(OH)D level was 15.8 ± 6.5 ng/ml at baseline and became 77.2 ± 30.5 ng/ml at 3 d (P <0.001) and 62.4 ± 26.1 ng/ml at 30 d (P <0.001). PTH levels concomitantly decreased from 53.0 ± 20.1 to 38.6 ± 17.2 pg/ml at 3 d and to 43.4 ± 14.0 pg/ml at 30 d (P <0.001 for both). The trends were maintained in a subgroup followed up to 90 d (P <0.001). Mean serum Ca and P significantly increased compared to baseline, whereas serum Mg decreased at 3 d. 1,25-Dihydroxyvitamin D significantly increased from 46.8 ± 18.9 to 97.8 ± 38.3 pg/ml at 3 d (P <0.001) and to 59.5 ± 27.3 pg/ml at 60 d (P <0.05). Conclusions: A single oral dose of 600,000 IU of cholecalciferol rapidly enhances 25(OH)D and reduces PTH in young people with vitamin D deficiency.