Findings: ICU assistance was required by 110 (11.8%) participants. Out of 551 patients treated with calcifediol at admission, 30 (5.4%) required ICU, compared to 80 out of 379 controls (21.1%; p<0.0001). Logistic regression of calcifediol treatment on ICU admission, adjusted by age, gender, linearized 25(OH)D levels at baseline, and comorbidities showed that treated patients had a reduced risk to require ICU (RR 0.18 [95% CI 0.11;0.29]). Baseline 25(OH)D levels inversely correlated with the risk of ICU admission (RR 0.53 [95% CI 0.35;0.80]). Overall mortality was 10%. In the Intention-to-treat analysis, 36 (6.5%) out of 551 patients treated with calcifediol at admission died compared to 57 patients (15%) out of 379 controls (p=0.001). Adjusted results showed a reduced mortality for more of 60%. Higher baseline 25(OH)D levels were significantly associated with decreased mortality (RR 0.40 [95% CI 0.24;0.67]). Age and obesity were also predictors of mortality.