This article re-evaluates the literature on vitamin D and fracture reduction, highlighting the relevance of new understandings for fracture prevention. A new set of science-based research guidelines for clinical trials on vitamin D and fracture is proposed. The existing clinical trials on vitamin D and fracture are analyzed, focusing on studies that most closely meet the proposed guidelines. An estimation of the true fracture-reduction potential of therapeutic-level vitamin D supplementation is offered. The analysis outlined in this article leads to a series of striking conclusions. First, most of the available clinical trials and meta-analyses of vitamin D and fracture underestimate the true fracture reduction potential of vitamin D. Second, achievement of vitamin D serum sufficiency levels (now set in the United States, Europe, and many other places at a minimum of 32 ng per mL) could provide for a 50- to 60-percent fracture reduction. And third, providing for vitamin D sufficiency is the simplest, most life-supporting, and most cost effective means of significantly reducing the incidence of osteoporotic fractures worldwide. Given the urgent need, the Osteoporosis Education Project (OEP) has initiated a call for universal vitamin D repletion as the primary basis for osteoporotic fracture prevention worldwide.