Vitamin D in the ICU: anything new under the sun?

The recent recognition of the myriad roles of vitamin D beyond those of bone health and calcium homoeostasis has resulted in a large body of clinical studies demonstrating an association between vitamin D deficiency and a number of adverse health outcomes. While these studies in chronic disease states have shown a strong association between vitamin D deficiency and poor outcomes, they have been unable to demonstrate cause and effect. Several studies to date have demonstrated a high prevalence of vitamin D deficiency in critically ill patients, and some of these have shown an association with poor outcomes. It is possible that low vitamin D levels may contribute to the acute multiorgan dysfunction seen in critical illness by similar mechanisms to those seen in chronic conditions. In this commentary, we briefly review the physiology of vitamin D, examine the evidence for association of hypovitaminosis with poor outcome in both ambulatory and intensive care unit patients, and debate the role of routine vitamin D supplementation in the ICU.