Three patients died during the study, and the researchers found that they had the lowest levels of vitamin D in the study group.
Lee said the researchers don't know the exact cause of the vitamin D deficiency. A lack of sun exposure could play a role, as could a lack of dietary intake of vitamin D. But, Lee said, "it may be postulated that the tissue demand for vitamin D is increased during infection, metabolic disturbances and inflammation. Vitamin D may therefore be used up during critical illness. However, it is a hypothesis, and the relationship between vitamin D and critical illness requires further studies in the future."
Dr. David Weinstein, a nephrologist at Beaumont Hospital in Royal Oak, Mich., agreed that more research needs to be done to tease out what the cause of the vitamin D deficiency is, and studies need to be done to see if replacing the lost vitamin D would benefit these patients.
"We know that in stable situations, vitamin D deficiency definitely has a potential link to mortality, and vitamin D replacement does improve outcomes," said Weinstein. But, he added, "from this study, it's too early to tell if there would be a mortality benefit from vitamin D replacement." And for immobile patients, there's a risk of creating calcium levels that are too high, he added.
In the current study, 10 patients were given vitamin D supplements, and no protective effect was found.
Dr. Kirit Tolia, chief of endocrinology at Providence Hospital in Southfield, Mich., said his sense is that replacing vitamin D in such critically ill patients may be too late. "If you go into illness with a significant vitamin D deficiency, it makes whatever the underlying cause of the hospitalization worse," he said. For example, if someone is being treated for sepsis -- a serious infection -- if their vitamin D levels are low, it makes it harder for them to fight the infection, he explained.
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