BackgroundVitamin D deficiency in patients with cholestasis is due to impaired intestinal vitamin D absorption, which results from decreased intestinal bile acid concentration. Patients with cholestasis usually do not achieve optimal vitamin D status when a treatment regimen for children without cholestasis is used. However, data on high-dose vitamin D treatment in patients with cholestasis are limited.MethodsThis study is a prospective study that included pediatric patients with cholestasis (serum direct bilirubin > 1 mg/dL) who had vitamin D deficiency (serum 25-hydroxyvitamin D, 25-OHD, < 20 ng/mL). In Phase 1, single-day oral loading of 300,000 IU (or 600,000 IU if weight≥20 kg) of vitamin D2 was administered, followed by an additional loading if serum 25-OHD < 30 ng/mL, and 4-week continuation of treatment using a vitamin D2 dose calculated based on the increment of 25-OHD after first loading. In Phase 2, oral vitamin D2 (200,000 IU/day) was administered for 12 days, followed by 400,000 IU/day of vitamin D2 orally for another 8 weeks if serum 25-OHD < 30 ng/mL.ResultsPhase 1: Seven patients were enrolled. Three out of seven patients had a moderate increase in serum 25-OHD after loading (up to 20.3–27.2 ng/mL). These patients had conditions with partially preserved bile flow. The remaining four patients, who had biliary atresia with failed or no Kasai operation, had low increments of serum 25-OHD.Phase 2: Eleven patients were enrolled. Eight out of 11 patients had a moderate increase in serum 25-OHD after 200,000 IU/day of vitamin D2 for 12 days. Serum 25-OHD continued increasing after administering 400,000 IU/day of vitamin D2 for another 8 weeks, with maximal serum 25-OHD of 15.7–22.8 ng/mL.ConclusionVery high doses of vitamin D2 (200,000 and 400,000 IU/day) partly overcame poor intestinal vitamin D absorption and resulted in moderate increases in serum 25-OHD in pediatric patients with cholestasis, particularly when cholestasis was caused by uncorrectable bile duct obstruction.