Abstract: European Journal of Integrative Medicine 42 (2021) 101271 Contents lists available at ScienceDirect European Journal of Integrative Medicine journal homepage: www.elsevier.com/locate/eujim Clinical trial High dose vitamin D improves total serum antioxidant capacity and ICU outcome in critically ill patients - A randomized, double-blind clinical trial Mohammad Sistanizad a,b, Mehran Kouchek c, MirMohammad Miri c, Sara Salarian c, Seyedpouzhia Shojaei c, Fatemeh Moeini Vasegh a, Hossein Seifi Kafshgari d, Roja Qobadighadikolaei e,∗ a Department of Clinical Pharmacy, School of Pharmacy, Shahid Beheshti University of Medical Sciences, Tehran, Iran of Cardiovascular Disease Research Center, Shahid Beheshti University of Medical Sciences, Tehran. Iran of Critical Care Medicine, Imam Hossein Medical and Educational Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran d Faculty of Dentistry, Mazandaran University of Medical Sciences, Sari, Iran e Department of Clinical Pharmacy, School of Pharmacy, Guilan University of Medical Sciences, Rasht, Iran b Prevention c Department a r t i c l e i n f o Keywords: Vitamin D Total anti-oxidant Capacity Intensive care Mechanical ventilation Randomized controlled trial a b s t r a c t Introduction: Mechanical ventilation can increase the rate of free radicals in the systemic circulation due to its effect on the inflammatory system. Previous research has suggested that vitamin D has antioxidant properties. This study aimed to evaluate the effect of vitamin D on total Antioxidant Capacity (TAC) and its relationship with ICU patients’ outcomes. Methods: In this prospective randomized clinical trial, 36 ventilated ICU patients were randomly allocated to receive either a single intramuscular vitamin D 300,000 IU or its placebo. Serum Vitamin D and TAC were measured before and on day 7 after the intervention. Clinical Pulmonary Infection Score (CPIS) and sequential organ failure assessment (SOFA) scores were measured daily for seven days and on days 14 and 28. Results: Thirty patients completed the study. The results show that injection of vitamin D leads to a significant increase in the mean changes of vitamin D level on the seventh day of the study (+3.5±1.3 vs -0.4±0.2 P=0.00) and TAC levels (3.2±3.9 vs -2.0±2.6 P=0.00. ICU length of stay was 18.3±8.4 and 25.4±6.6 days in the intervention and placebo arms of the study. Twelve patients in the placebo group and 5 in the vitamin D group died within the 28 day study period. The duration of mechanical ventilation was 15.7± 9.3 vs. 22.6± 9.1 days in vitamin D and placebo arms, respectively. Conclusion: : Administration of vitamin D may increase TAC levels and decrease the length of stay and duration of mechanical ventilation in ICU patients.