The prevalence of vitamin D deficiency among intensive care unit (ICU) patients is potentially associated with an increased risk of mechanical ventilation, sepsis, prolonged hospital stays, and mortality. Although ICU patient care has significantly improved in recent years, the role of vitamin D supplementation remains under investigation. A literature review was conducted using PubMed, Web of Science, Embase, and Cochrane databases, focusing on randomized controlled trials published in the past five years on vitamin D supplementation in adult ICU patients. Patients' baseline vitamin D levels, administration routes, doses, biomarker changes, mechanical ventilation duration, length of hospital stay, and mortality were analyzed. Although vitamin D supplementation appears safe and may reduce ICU stay duration and mechanical ventilation time and improve SOFA scores, its impact on overall mortality remains uncertain. Routine supplementation for all ICU patients is not currently recommended
clinical decisions should consider individual baseline vitamin D levels, patient characteristics, severity of illness, doses, and administration methods.