A recent study published in JAMA found that administration of high dose vitamin D did not significantly reduce hospital length of stay, hospital mortality, or six-month mortality among critically ill patients, but did see a reduction in hospital mortality in those who were severely vitamin D deficient [25(OH)D < 12 ng/ml] at admission.
They used what is called an intention-to-treat analysis, which arethe results of an experiment based on the initial treatment group assignment and not on those who actually received treatment. That means their analysis included patients who did not take their vitamin D.
Hospitalized patients are at high risk for vitamin D deficiency. Being confined to a hospital bed means limited access to outdoor sun exposure and subsequent vitamin D production.
Vitamin D is very important to this patient population who are also at risk for complications from surgery and hospital-acquired infections. These, among other things, may increase length of hospital stay, and risk for morbidity and mortality.