25-Hydroxyvitamin D Pharmacokinetic Study

Inclusion Criteria: * Adult male or female with history of intestinal fat-malabsorption with confirmed diagnosis * Taking vitamin D (ergocalciferol or cholecalciferol). Subjects taking vitamin D supplement of more than 2000 IUs (50 micrograms)/day) that may interfere with study endpoints must be willing and able to discontinue use of these supplements for the duration of the study and allow for at least a 14-day washout prior to prescreening and enrollment. * Women of child bearing potential must be on birth control and not pregnant based on a negative pregnancy test at baseline for each of the 2 pharmacokinetic studies. * Serum total 25(OH)D \< 30 ng/mL Exclusion Criteria: * Unwilling to discontinue use of supplemental dose of vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol) daily equivalent (2,000 IU/50 μg) 1 week or less prior to randomization and during the study * On medications that can affect vitamin D metabolism including steroids such as prednisone, anti-seizure medications and medications to treat HIV. * Tanning in a tanning bed at least one week before the study and throughout the duration of this study. * Anyone anticipating going on holiday (where exposure to sun is imminent) 1 week before or during the entire study. * Participation in the study or any reason which, in the opinion of the investigator makes adherence to a treatment or follow-up schedule unlikely * History of elevated serum calcium * Chronic hepatic or renal failure * Subjects with a history of an adverse reaction to orally administered vitamin D. * Inability to give informed consent