© 2019 Published by Oxford University Press on behalf of the Association of Military Surgeons of the United States. Purpose To explore response to vitamin D supplementation in active duty (AD) warfighters and translate findings into evidence-based health policy. Background Soldiers are at risk for musculoskeletal injuries and metabolic dysfunction that impact physical performance and military readiness; the link with low vitamin D status is unclear. Methods This prospective trial enrolled 152 soldiers; baseline 25 hydroxyvitamin (OH) D level determined assignment to a no-treatment control (CG) or treatment group (TG) receiving a vitamin D 3 supplement for 90 days. Symptoms, diet, sun exposure, and blood biomarkers obtained at baseline (T1) and 3 months (T2). Results Cohort was predominantly white (58%) with a significant difference in racial distribution for vitamin D status. Mean (SD) 25(OH)D levels were 37.8 (5.6) ng/mL, 22.2 (5.0) ng/mL, and 22.9 (4.7) ng/mL for the CG, low dose TG, and high-dose TG at T1, respectively. Following three months of treatment, one-way ANOVA indicated a statistically significant difference between groups (F 5,246 = 44.37; p < 0.0001). Vitamin D intake was 44% of Recommended Dietary Allowance throughout the first phase of the trial. Patient-Reported Outcomes Measurement Information System scores improved in TG for fatigue and sleep, p < 0.01. Conclusions Vitamin D deficiency is widespread in AD soldiers. Clinicians must intervene early in preventable health conditions impacting warfighter performance and readiness and recommend appropriate self-care strategies.