Cholecalciferol(25-[OH]-Vitamin D) in Treating Patients With Colorectal Cancer

Inclusion Criteria: * Patients with a suspected diagnosis of adenocarcinoma of the rectum or sigmoid colon (e.g. based on appearance of mass or histology) referred to colorectal surgery who are expected to undergo routine proctosigmoidoscopy or flexible sigmoidoscopy in the surgeon's office as well as resection and/or endorectal ultrasound (EUS) as part of their routine care * The tumor must be accessible for biopsy and suitable for multiple biopsies * Eastern Cooperative Oncology Group (ECOG) performance status of =\< 2 * Able to understand and willing to sign written informed consent document Exclusion Criteria: * Prior anti-cancer therapy for this cancer such as chemotherapy, biologic therapy, immune therapy or radiation therapy * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements * Unable to swallow capsules * Underlying condition that will interfere with absorption of orally ingested vitamin D, e.g., untreated fat malabsorption * History of allergic reaction to cholecalciferol or other vitamin D preparations * EXCLUSION CRITERIA FOR DOSING VITAMIN D: * Elevated ionized calcium * Primary hyperparathyroidism * Renal failure with estimated glomerular filtration rate \< 20 mL/min/1.73m\^2 as calculated using the Modification of Diet in Renal Disease (MDRD) study equation for the isotope dilution mass spectrometry (IDMS) - traceable creatinine methods reported by University Hospital Case Medical Center (UHCMC) laboratory (due to less active formation of 1,25 hydroxyvitamin D due to less hydroxylase) * Serum 25-OH-vitamin D \> 40 ng/ml