Vitamin D Supplement Study for Stage Three and Four Chronic Kidney Disease (CKD) Patients

Inclusion Criteria: * Adults ≥ 18 years * Chronic kidney disease stage 3-4 (eGFR 15-59 mL/min/1.73m2 body surface area, calculated using the MDRD Study equation GFR calculator) * Hypovitaminosis D (serum 25OHD \< 31 ng/mL) * Secondary hyperparathyroidism (Intact PTH \> 70 pg/mL for stage 3, and iPTH \> 110 pg/mL for stage 4) Exclusion Criteria: * Initiation of vitamin D therapy between the time of the lab draw used for screening and the screening process * History of liver failure * History of intestinal malabsorption or chronic diarrhea * Serum calcium level greater than 10.2 mg/dL * Treatment with an activated vitamin D formulation (calcitriol, doxercalciferol or paricalcitol) within the past 6 months * Treatment with phenobarbital, phenytoin, rifampicin, sucralfate, steroids, digoxin, or other medications that could affect vitamin D metabolism * Primary hyperparathyroidism, active of a prior history of such * Active malignancy excluding basal cell or localized squamous cell skin cancer * Subject is pregnant (e.g. positive HCG test) or breast-feeding * Refusal to use highly effective contraceptive measures (as determined by the investigator) throughout the treatment phase of the study * Serum phosphorus level greater than 4.5 or treatment with an oral phosphate binder within the past 6 months * Treatment with cinacalcet or other calcimimetic within the past 6 months * Anticipated dialysis within 6 months after randomization * Inability to swallow tablets * Known sensitivity, intolerance, or other adverse response to the study drugs which would prevent compliance with study medication * Have an unstable medical condition, defined as having been hospitalized within 30 days before screening, the expectation of recurrent hospital admissions or life expectancy of less than 6 months in the judgment of the investigator * Subject is currently enrolled in, or fewer than 30 days have passed since subject has completed another investigational device or drug study(s); or subject is receiving another investigational agent(s). * Current treatment with vitamin D 50,000 IU