Fig. 2.

Need for additional Ca to reduce the risk of hip fracture with vitamin D supplementation. Evidence from a comparative meta-analysis of randomized controlled trials that oral vitamin D appears to reduce the risk of hip fracture only when Ca supplementation is added. The figure shows two forest plots of the risk of hip fracture between vitamin D and either placebo/no-treatment groups (left panel) or between vitamin D and Ca and placebo/no-treatment groups (right panel). The pooled estimate of the relative risk was statistically significant only with the combination of vitamin D and Ca. Adapted from Boonen et al. [28].