A view on vitamin D: a pleiotropic factor?

Vitamin D is precursor of the steroid hormone calcitriol and has important functions throughout the body, including increasing intestinal absorption of calcium, magnesium and phosphate. Vitamin D deficiency has been linked with a range of disorders, including several bone diseases. However, large trials of vitamin D supplementation have produced mixed results. Here, experts from around the world discuss several key questions in the vitamin D research and clinical fields.