Effects of Vitamin D in Patients With Breast Cancer

Inclusion Criteria: 1. Histologically confirmed female primary breast cancer patients whose surgery is planned for the next 2-8 weeks without neoadjuvant therapy as assessed by multidisciplinary team 2. Age ≥18 years 3. Clinically palpable tumour(s) (greater than or equal to 2 cm) 4. Normal serum and urine calcium and serum PTH values at baseline (as defined by Ottawa Hospital) 5. Written informed consent for study Exclusion Criteria: 1. Patients with recurrent or metastatic breast cancer 2. History of neoadjuvant hormonal therapy, chemotherapy, or radiation therapy in the last 6 months for their breast cancer or any other cancer treatment 3. ECOG performance Status \> 2 4. Hypercalciuria on initial baseline urine, defined as Ca/Creatinine Ratio\> 1.0 5. Current or previous history of urolithiasis or hyperparathyroidism 6. Abnormal hepatic function according to Ottawa Hospital norms (Total Bilirubin \>2x upper limit of normal, ALT/AST \>3x upper limit of normal)and/or abnormal renal function (Creatinine \> 150 µmol/L) 7. History of granulomatous disease such as tuberculosis or sarcoidosis. 8. Intake of Vitamin D (cholecalciferol) supplement ≥ 2000 IU/day within the last 2 months 9. Inability to comply with a study protocol in the opinion of the investigator (such as abuse of alcohol, drugs or psychotic states).