Purpose: Low vitamin D blood levels are associated with high mortality in critically ill patients. There is controversy about vitamin D supplementation in this population. The objective of this meta-analysis was to evaluate if vitamin D administration reduces mortality in critically ill patients.

Materials and methods: Online databases were searched up to September 1^st, 2016 for randomized placebo-controlled trials on the use of vitamin D in adult patients with critical illness. The primary end point was mortality among trials with low risk of bias. The secondary end points were length of hospital stay, length of intensive care unit stay, length of mechanical ventilation, and adverse events.

Results: Seven studies published between 2011 and 2016, for a total of 716 patients, were included in the analysis. Vitamin D administration was associated with significantly lower mortality compared with placebo (101/320 [32%] in the vitamin D group vs 123/307 [40%] in the placebo group; odds ratio, 0.70 [95% confidence interval, 0.50 to 0.98]; P=.04; I²=0%). No differences in adverse events and other secondary end points were found.

Conclusions: In critically ill patients, vitamin D administration might be associated with a reduction in mortality without significant adverse events. A large multicenter randomized trial should conclusively confirm these findings.