This research addressed bone health. Bone health1–3 Robert P Heaney ABSTRACT Much evidence indicates that both calcium and vitamin D are effi- cacious in protecting the skeleton, particularly when these 2 nutri- ents are used in. Each nutrient is necessary for the full expression of the effect of the other, and where their actions are independent, their effects on skeletal health are complementary. These findings have important implications for understanding vitamin d in MS and improving patient outcomes. The results may inform clinical practice and guide development of more effective MS treatments.