Vitamin D deficiency and acute lung injury

Acute Lung Injury (ALI) and the more severe form Acute Respiratory Distress Syndrome (ARDS) remain a significant cause of morbidity and mortality in the critically ill patient. It is characterised by a severe inflammatory process resulting in diffuse alveolar damage, influx of neutrophils, macrophages and a protein rich exudate in the alveolar spaces caused by endothelial and epithelial injury. Improvements in outcomes are in part due to restrictive fluid management and protective lung ventilation however successful therapeutic strategies remain elusive with promising therapies failing to translate positively in human studies. The evidence for the role of vitamin D in lung disease is growing - deficiency has been associated with impaired pulmonary function, increased incidence of viral and bacterial infections and inflammatory disease including asthma and COPD. Studies have also reported a high prevalence of vitamin D deficiency in the critically ill and an association with adverse outcomes. Although exact mechanisms are yet to be discerned, vitamin D appears to impact on a variety of inflammatory and structural cells within the lung including macrophages, lymphocytes and epithelial cells. To date there are few directly supportive clinical studies in ALI; this review explores the compelling evidence suggesting arole for vitamin D in ALI and the mechanisms by which it could contribute to pathogenesis.