High Dose Vitamin D vs Standard Dose Vitamin D Study

Treatments with anti-estrogen agents for hormone receptor positive breast cancer is the most efficacious of systemic therapies, with aromatase inhibitors (AI's) being considered the most active anti-estrogen therapy in early stage breast cancer. But, use of these treatments has been shown to cause musculoskeletal (joint/muscle) side effects that sometimes cause patients to discontinue the use of them. Also, Vitamin D deficiency is a well know cause of a wide array of musculoskeletal issues. There is evidence that Vitamin D supplementation may help prevent arthralgia while on AI's. Therefore, the investigators want to see if giving a higher dose of Vitamin D could decrease the incidence of AIA as compared to a standard dose of Vitamin D. The investigators believe that this could possibly result in patients continued treatment with AI therapy for hormone receptor positive breast cancer.