Vitamin D Deficiency, Muscle Pain, Joint Pain, and Joint Stiffness in Postmenopausal Women Receiving Letrozole For Stage I-III Breast Cancer

Inclusion Criteria: * Patients must have a histologically confirmed diagnosis of Stage I, II or III breast carcinoma * Patients must be prescribed letrozole for adjuvant breast cancer treatment * Prior adjuvant tamoxifen is permitted * Patients must be postmenopausal; for study purposes, postmenopausal is defined as: a prior documented bilateral oophorectomy, or a history of at least 12 months without spontaneous menstrual bleeding, or have a persistently postmenopausal estradiol in the past 6 months without menses, and clinically in menopause at the judgment of the treating physician, or age 60 or older with a prior hysterectomy without oophorectomy, or age less than 60 with a prior hysterectomy without oophorectomy (or in whom the status of the ovaries is unknown), with a documented FSH level demonstrating confirmatory elevation in the postmenopausal range for the lab Exclusion Criteria: * Diagnosis of Stage IV breast carcinoma * Pre-existing myalgias, arthralgias and/or joint stiffness \>= Grade 1, as defined using CTEP CTC identified during baseline physical exam * Inability to understand or cooperate with study procedures * Receipt of investigational drug within 30 days before study entry * Lack of physical integrity of the upper gastrointestinal tract or malabsorption syndrome * Unwillingness to give informed consent * Unwillingness to participate or inability to comply with the protocol for the duration of the study * Patients with serum calcium \>= 14 mg/dL * Patients with renal dysfunction defined as glomerular filtration rate \<10ml/min calculated using Cockroft-Gault equation