Personalized Vitamin D Supplementation for Reducing or Preventing Fatigue and Enhancing Quality of Life of Patients with Colorectal Tumor: Randomized Intervention Trial

Interventions: Group 1: Dekristol (ATC A11CC05, colecalciferol), PO (capsule), for 84 days. Individualized loading dose based on individual 25-hydroxyvitamin D levels and BMI (20,000 or 40,000 IU daily on day 1 to 11, in sum, on average approx. 180,000 IU) followed by a maintenance dose of 2,000 IU daily for the remaining days. Group 2: Control: Placebo for 84 days Primary outcome(s): Mean difference in FACIT-F fatigue subscale between intervention and placebo group in week 13 to 16. A mean difference = 3 FACIT-F fatigue subscale points will be considered a clinically relevant difference. Study Design: Allocation: Randomized controlled study; Masking: Blinded (masking used); Control: placebo; Assignment: parallel; Study design purpose: treatment