The human immune system produces a protein called hCAP18 (also known as LL-37 or cathelicidin). This protein is believed to help the body to fight infections. Studies suggest that vitamin D may important in the production of hCAP18. This study is designed to test the ability of two different forms of vitamin D to affect levels of hCAP18. Vitamin D and hCAP18 levels will be measured during an initial visit. Individuals who are vitamin D deficient will be randomly assigned to receive one of two forms of vitamin D for two weeks. After this, follow-up levels will be measured.