Vitamin D Supplementation in Orthopedic Trauma: Influence on Immune Modulation, Fracture Healing, and Infection Outcomes.

Vitamin D deficiency is a common and correctable problem in orthopedic patients, increasingly recognized for its impact on infection risk, delayed fracture healing, and poor surgical outcomes. Beyond its role in maintaining calcium and phosphate balance, vitamin D supports immune and bone health by promoting antimicrobial peptide production, macrophage activity, and osteoblast function, all of which are essential for infection control and bone repair. This review draws on studies in adult orthopedic populations that assessed vitamin D status in relation to surgical site and periprosthetic infections, fracture healing, nonunion, and fracture prevention. Across these studies, deficiency below 30 ng/mL was found in 43-90% of patients. This widespread deficiency was consistently linked to higher infection rates, with infected patients showing lower vitamin D levels at surgery. Postoperative levels decline by up to 40%, which can worsen existing insufficiency during the critical early recovery period when infection risk is highest. Observational and prospective data show that ongoing deficiency delays or prevents fracture union, with registry and cohort studies confirming a measurable rise in nonunion risk. Overall, the evidence supports vitamin D as a modifiable factor influencing orthopedic recovery. Routine screening and supplementation of at least 800 IU daily to maintain serum levels above 30 ng/mL are simple, safe, and inexpensive measures that can reduce infections, support bone healing, and lower fracture risk. Hospitals should incorporate vitamin D screening, correction, and maintenance into standard orthopedic care. This narrative review summarizes current evidence on vitamin D and orthopedic outcomes and provides practical guidance for its perioperative management.