Ph I/II of Vitamin D on Bone Mineral Density & Markers of Bone Resorption

Inclusion Criteria: 3.1.1 All postmenopausal women with histology-confirmed invasive primary breast cancer, who have completed primary surgical or radiotherapy (XRT) with or without adjuvant chemotherapy and are candidates to receive adjuvant therapy with aromatase inhibitors will be screened for eligibility. Postmenopausal is defined as satisfying one or more of the following criteria: having had bilateral oophorectomy; aged more than 60 years; or aged 55-59 years with an intact uterus and amenorrheic for at least 12 months; or if amenorrheic for less than 12 months (after receiving hysterectomy, hormone therapy or chemotherapy). 3.1.2 At the time of study enrollment, participants will have completed primary surgical or XRT with or without adjuvant chemotherapy. Chemotherapy will be completed at least 28 days prior to enrollment. 3.1.4 Participants will be women between 18-85 years of age. Women and minorities will be actively recruited. Though breast cancer extremely rarely occurs in children and men, this study will only recruit adult females. 3.1.5 Participants will have a life expectancy of at least 5 years. 3.1.6 Participants will have Eastern Clinical Oncology Group (ECOG) performance status 0-2. 3.1.7 Ability to understand and the willingness to sign a written informed consent document Exclusion Criteria: 3.2.1 Medications affecting bone metabolism (bisphosphonates, anticonvulsants, chronic heparin therapy, chronic glucocorticoid use \> 5 mg/day prednisone or equivalent, teriparatide). 3.2.2 Use of any investigational drug within past 90 days. 3.2.3 Metastatic breast cancer. High risk for osteoporosis/fractures (BMD \< -2.0, history of non-traumatic fracture). Hyperparathyroidism Hypercalcemia Hypercalciuria (fasting spot urine calcium/creatinine ratio \>0.20) History of renal stones Renal failure with creatinine over 2.0 3.2.4 Considering that vitamin D3 is produced by the human body, allergy to vitamin D3 is not expected to develop. Subjects with known history of allergic reaction to compounds used to manufacture capsules (rice powder) will be excluded form this study. 3.2.5 Recent history of excessive alcohol or drug use. 3.2.6 As this study will recruit post-menopausal patients, thus pregnant or nursing patients are not part of this investigation. 3.2.8 This study is designed to study women after completing primary therapy for breast cancer. Survivors of previous cancers and HIV-positive subjects will not be excluded.