Activated Vitamin D for the Prevention and Treatment of Acute Kidney Injury

Inclusion Criteria: * Age ≥ 18 * Admitted to the ICU within 48h prior to enrollment * Likely to remain in the ICU (alive) for ≥72h * Naso/orogastric tube or ability to swallow * High risk of severe AKI Exclusion Criteria: * Serum total calcium \> 9.0 mg/dl or phosphate \> 6.0 mg/dL within previous 48h * Currently receiving oral calcium supplementation * Ingestion of vitamin D3 \>1,000 IU/day or any 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D during the previous 7 days * AKI stage 2 or 3 (based on KDIGO serum creatinine and/or urine output criteria) * History of transplantation or receiving chronic (\>7days) of immunosuppressive medications (not including glucocorticoid steroids at a dose less than or equivalent to prednisone 20 mg/day) * Neutropenia in the previous 48h * Active primary parathyroid disease, active granulomatous disease, or symptomatic nephrolithiasis in the previous 3 months * Receiving cytochrome P450 inhibitors * Chronic Kidney Disease stage V or End Stage Renal Disease * Hemoglobin \< 7 g/dL * GI malabsorption * Prisoner * Pregnancy or breast feeding