['To heighten awareness of the problems related to the high prevalence of suboptimal vitamin D status in hospitalized patients and the general population, including an overview of vitamin D biology, how vitamin D status is defined, the negative health issues associated with suboptimal vitamin D status, indications for treatment, treatment strategies, and controversies in the field.', "(a) Literature review was performed using PubMed and CINAHL databases to locate and review medical, nursing, and nutritional journals. (b) Authors' recent prospective studies of 100 patients in a general tertiary hospital rehabilitation unit and 51 nonhospitalized volunteers."] Is suboptimal vitamin D status a highly prevalent but treatable condition in both hospitalized patients and the general population?