A Prospective Open-label Comparison of Two Vitamin D3 Repletion Strategies in Vitamin D Deficient Patients

The purpose of this study is to determine whether one of two Vitamin D3 (cholecalciferol) oral treatment regimens is superior to the other in normalizing Vitamin 25 OHD serum levels. While these two regimens in the end provide equal total dosing, the two arms differ in frequency and dosing during a 40 day treatment plan. The primary endpoint will be a direct comparison of two dosing regimens of Vitamin D3 repletion at day 40 (+/- 3 days) using a paired T-test. Secondary endpoints include record of adverse events throughout the 40 day study period as well as changes in basic laboratory values including CMP and ionized Calcium. The investigators hypothesize that the Cholecalciferol (Vitamin D3) daily dosing arm of 5000 IU daily will result in more efficient replacement as compared to the 50,000 IU dosing given every 10 days. Our goal will be to achieve a serum Vitamin 25 OH D level of \> 50 mg/dL at day 40. The investigators propose that 75% of the subjects on daily Vitamin D3 will achieve this level and that 35% of the subjects in the every 10 days dosing arm will reach this goal.