Immune Mechanisms of Vitamin D to Reduce Chronic Pain After Burn

Inclusion Criteria * ≥ 18 years and ≤ 70 years of age * MThBI severe enough to warrant admission to Burn Surgery Service (NOTE: surgery may or may not be indicated) * Admission and subsequent enrollment occurs within 1 week of MThBI * Patients experience a thermal burn injury, not an electrical or chemical burn. * Has a smartphone with continuous service \>1 year * Alert and oriented * Willing to take study medication (6 capsules of Vitamin D or placebo) * Point of care Vitamin D level \<100 ng/mL * Able to speak and read English * Burn survivors with acute pain severity ≥ 7/10 on the Numeric Rating Scale (initial pain severity reported by patient on screening) * Total Body surface area burned \<30% Exclusion Criteria * Substantial comorbid injury (e.g. long bone fracture) * Pregnancy/Breastfeeding * Prisoner status * Active psychosis, suicidal ideation, or homicidal ideation * Requires an emergency/bedside escharotomy or fasciotomy for the treatment of burn injury. * Known Child-Pugh liver disease severity classification B or C. * Known chronic kidney disease stage 4 or higher (GFR≤29). * No other history or condition that would, in the investigator's judgment, indicate that the patient would very likely be non-compliant with the study or unsuitable for the study (e.g. might interfere with the study, confound interpretation, or endanger patient). * Intubated and sedated at time of enrollment. * Hypersensitivity to Vitamin D3, ergocalciferol, calcitriol, alfacalcidol, calcipotriol * Known hypercalcemia (based on routine admission laboratory assessment). * Sarcoidosis * Hyperphosphatemia (based on routine admission laboratory assessment) * Taking Vitamin D supplements in excess of 800 IU daily.