Merlijn T, et al. - Given that vitamin D deficiency is associated with increased fracture risk in older persons, authors developed an externally validated simple prediction model to ascertain insufficient serum 25-hydroxyvitamin D (25(OH)D) status in older women at risk for fractures. The presence of vitamin D insufficiency in women at risk for fractures could be predicted with this externally validated model, which included age, BMI, vitamin D supplementation, multivitamin supplementation, calcium supplementation, daily use of margarine, fatty fish ≥ 2×/week, ≥ 1 hours/day outdoors in summer, season of blood sampling, the use of a walking aid and smoking as predictors. The chosen 25(OH)D threshold greatly determines the potential clinical benefit of this tool, which decreases when a higher threshold is used.