One hundred and two patients with acute tibia and femur fractures were included in this Phase II screening randomized trial comparing the effect of high loading dose Vitamin D3 supplementation (n=27), high daily dose supplementation (n=24), low daily dose supplementation (n=24) and placebo (n=27) on the improvement of fracture healing. Primary outcomes of interest were clinical fracture healing (as assessed by the Function IndeX for Trauma [FIX-IT]) and radiographic fracture healing (as assessed by the Radiographic Union Score for Tibial fractures [RUST]). High dose Vitamin D3 supplementation (loading or daily) was found to provide modest benefits in clinical fracture healing compared to placebo at 3 and 12 months. However, the effectiveness of Vitamin D3 supplementation for improving non-osteoporotic fracture healing is still debatable, and larger studies are required.