Vitamin D status in adult critically ill patients in Eastern India: An observational retrospective study.

Sir,

This is in response to an article entitled, ‘Vitamin D status in adult critically ill patients in Eastern India: An observational retrospective study,’ published in Lung India (2014;31:212-6).[1] The authors deserve compliments for their effort. However, I have a few concerns with this study. The concerns are mainly with the conclusion that the authors have drawn from their study. The authors conducted this study in a retrospective study design among all patients admitted to the adult Medical Intensive Care Unit (MICU), between March 2013 and August 2013, in a teaching medical college of Eastern Orissa. Subsequently, the authors selected a subset of available patients (those wherein levels of 25(OH) D was available) were included in the study. The ideal manner to conduct this study would have been to study it in the case–control mode.

On the basis of this study, the authors conclude that, “patients with 25 (OH) D deficiencies in the MICU have increased hospital mortality, longer mechanical ventilation, and longer MICU stay”. The concerns are based on a few basic points. As pointed out by the authors the study showed that Vitamin-D insufficiency/deficiency was common among individuals with increased hospital mortality, longer mechanical ventilation, and longer MICU stay. To establish this statement, the study should have reflected on the fact that a condition (vitamin-D deficiency in this case) was common in one population (patients with increased hospital mortality, longer mechanical ventilation, and longer MICU stay in this case) in comparison with some other population or the general population. The conclusion drawn by the authors was further complicated by the fact that vitamin-D deficiency was being widely reported not just in India, but across populations worldwide. Studies estimated that one billion people worldwide had vitamin D deficiency or insufficiency.[2] There was widespread prevalence, with varying degrees (50-90%) of vitamin D deficiency, with low dietary calcium intake, in the Indian population, according to various studies published earlier.[3]

This takes us to a few important aspects of this study. Even as the study sample has been automatically drawn from a large general population in a state of vitamin D deficiency, to establish the relation between Vitamin D deficiency and increased hospital mortality, longer mechanical ventilation, and longer MICU stay, a more rigorous and robust study design must have been used, maybe a case–control study design would have been helpful. Furthermore, establishing conclusions on a subset of study participants, who had undergone vitamin D deficiency as part of the medical laboratory surveillance (investigations), sounds methodologically incorrect. At best, we can draw a vague association, just short of a conclusive statement.