Vitamin D is an essential hormone for achieving an optimal bone physiology. There is no universal consensus nowadays on the definition of hypovitaminosis D and cut-off values have been refined in the last years. The aim of this review is to analyze vitamin D deficiency among osteoporosis risk populations, including elderly and postmenopausal women, in Spain and other countries. We also review vitamin D supplementation: current clinical guidelines, last clinical studies, safety, and prescription schemes.