Implications of Vitamin D Deficiency in Critically Ill Children

Vitamin D is now considered to have additional beneficial roles besides traditional concept of its bone health benefit. With the discovery of receptors for vitamin D in various tissues including immune-regulating cells, heart and brain its role in the extra skeletal ‘pleiotropic effects’ has been extensively studied in the last few years. Following its synthesis mostly in kidney, calcitriol is transported to its site of action in the blood stream by vitamin D binding protein (DBP). Pleiotropic effect of calcitriol in potentiation of antimicrobial action, immunomodulation and cardioprotection is of relevance to the critical illness [1]. In developing countries, where infectious etiologies are the major causes of Pediatric Intensive Care Unit (PICU) admission, pleiotropic role of calcitriol in the immune system would be of utmost importance. It has been hypothesized that calcitriol, in monocytes, a part of innate immune system, stimulates cathelicidin, a peptide which has bactericidal, antiviral, antifungal and mycobactericidal properties [2]. Besides this, pleiotropic action on cardiovascular, respiratory and renal system would also be beneficial. Because of its hypothesized beneficial role in various organ systems, there has been tremendous interest in research globally regarding significance of vitamin D deficiency (VDD) with the hope that vitamin D may be the modifiable risk factor in intensive care. Since the first publication in NEJM in 2009 [3] by the Australian group, there has been rapid surge in publications in last few years in adult ICUs. Majority of them showed suboptimal 25OHD level and there was a significant association with higher risk of mortality. There have been few RCTs to normalize the suboptimal vitamin D using high dose cholecalciferol. The results are promising and researchers highlight the need for larger therapeutic trials [4–7]. In contrast, the role of vitamin D in critically ill children is less studied. The initial reports were published in 2012 from Boston Children’s Hospital PICU and Canadian Critical Care Trial group, who noted prevalence of VDD of 40 and 69 % respectively at the initiation of the care [8, 9]. Single centre reports from Australia and Spain showed slightly lower prevalence of 35 and 30 % respectively [10, 11]. Subsequently, couple of studies showed the prevalence to the range of 60 and 75% [12, 13]. Many of these studies are from North America, Australia and Europe. There are not many studies from Asia and tropical countries. The Boston group, in its cohort of 511 medical PICU patients, demonstrated an association between lower vitamin D level and higher illness severity score and increasing vasopressor use correlated with low vitamin D level [8]. Canadian Critical Care Trial group, in its mixed medical and surgical (non-cardiac) cohort, observed that VDD was independently associated with increased PICU length of stay by 2 d and higher illness severity score [9]. Besides these two studies, rest of the studies done in mixed ICU did not find any association between VDD and illness severity or adverse clinical outcomes [10–13]. Although it is clear that VDD is common in critically ill children, there are inconsistencies between studies to draw a firm conclusion on its association with severity of illness and morbidity. When we talk in context of India there is paucity of data on the issue in critically ill children. For this reason, the work reported by Prasad et al. on the estimation of vitamin D status in critically ill children from India in this issue of the Journal is important [14]. The authors reported the prevalence of vitamin D deficiency in a * Rakesh Lodha rakesh_lodha@hotmail.com