In addition to the baseline, and weeks 6, 12, and 18 visits, subjects randomized to the high-dose treatment arm will return at Weeks 3 and 9 to assess for symptoms of vitamin D toxicity. If a subject in the high-dose arm is found to exhibit evidence of vitamin D toxicity at the week 12 visit, he/she will be asked to return to their clinical research site for an additional vitamin D toxicity assessment at week 15. Study personnel will record each subject's interval history, assess adverse events, disease activity, and collect samples for safety and mechanistic assessments.