الفهرس 
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Abstract
Vitamin D is essential for bone health and optimal cardiovascular and innate immune functions (Enioutina,et al,2009) . Vitamin D, a nutrient derived from both diet and sunlight, has been increasingly recognized as pivotal to good health . A pleiotropic hormone , vitamin D has been increasingly implicated in the proper Afunctioning of multiple organs , its deficiency is associated with cardiovascular disease, asthma, multiple sclerosis, diabetes, acute lower respiratory infection (ALRI) and cancer (Dobnig et al., 2008).
One of the most important roles of vitamin D is to maintain skeletal calcium balance by promoting calcium absorption in the intestines, promoting bone resorption by increasing osteoclast number, maintaining calcium and phosphate levels for bone formation, and allowing proper functioning of parathyroid hormone to maintain serum calcium levels (Bell et al., 2010).
Although poor nutritional status is recognized as a risk factor for adverse outcomes in critical illness, there are no published studies investigating the potential role of vitamin D deficiency in pediatric critical illness (Mehta and Duggan, 2009).
The level of 25(OH)D needed for adequate immune and cardiovascular function is unclear. Vitamin D deficiency has been associated with increased viral respiratory infections and sepsis in children and adults (Ginde et al., 2011). It was recently hypothesized that vitamin D deficiency could also contribute to or prolong critical care pathophysiology (McNally et al., 2009 and Lee et al., 2009).