Participants who agree to have extra blood drawn to test for vitamin D levels in the blood will have 1 teaspoon of blood drawn at the following times: start of treatment, at the end of the first month of treatment, at the start of the continuation phase, and at the end of treatment. Participants will receive the results of these tests. If the vitamin D level is low, the study doctor will recommend that the participant take a vitamin D supplement. Participants may choose not to have blood drawn to check vitamin D levels, or may choose not to take the vitamin D supplement.