At present, there is no clinical reference data on how much the concentration of calcifediol in the blood increases after supplementing with vitamin D for Taiwanese ICU patients. This study aims to investigate the effects of enteral supplementation of vitamin D in critically ill patients with vitamin D deficiency. The results of the study are expected to provide clinical reference data to intensivists to select adequate dosage of vitamin D supplementation for their patients with vitamin D deficiency.

This is a multi-center, randomized clinical trial. ICU patients will receive vitamin D level examination. If the subject's blood calcifediol concentration is less than 20 ng / mL, the subject will be included in this clinical trial. Patients who are suitable to enteral supplement of vitamin D will be randomly divided to group Control (no vitamin D supplement) and group Vitamin D (enteral supplement of 569,600 IU vitamin D). The vitamin D level will be measures at specific time points.

Vitamin D deficiency patients have longer hospital stays, higher medical expenditures, and higher sepsis-related mortality. The preliminary results of 145 ICU patients of the Northern Medical Centers in Taiwan in our ongoing multicenter clinical trial showed that the mean calcifediol concentration was about 20.9 ng/mL, much lower than the normal value of 30-60 ng/ml. An Austrian randomized clinical trial has shown that supplementation of high-dose vitamin D in critically ill patients with vitamin D deficiency can reduce patient mortality, so it is important to treat critically ill patients with vitamin D deficiency. At present, there is no clinical reference data on how much the concentration of calcifediol in the blood increases after supplementing with vitamin D for Taiwanese ICU patients. This study aims to investigate the effects of enteral supplementation of vitamin D in critically ill patients with vitamin D deficiency. The results of the study are expected to provide clinical reference data to intensivists to select adequate dosage of vitamin D supplementation for their patients with vitamin D deficiency.

This is a multi-center, randomized clinical trial. ICU patients will receive vitamin D level examination. If the subject's blood calcifediol concentration is less than 20 ng / mL, the subject will be included in this clinical trial. Patients who are suitable to enteral supplement of vitamin D will be randomly divided to group Control (no vitamin D supplement) and group Vitamin D (enteral supplement of 569,600 IU vitamin D). The vitamin D level will be measures at specific time points. The patients' diagnosis, vital signs, laboratory data, 30-day survival, and 90-day survival will be recorded.

Inclusion Criteria:

• patients in intensive care units
• blood calcifediol concentration less than 20 ng / mL
• suitable for enteral feeding
• no ileus, vomit, or diarrhea

Exclusion Criteria:

• younger than 20 years old
• receive high dose vitamin D within 4 weeks (> 3000 IU pre day)
• hypercalemia ( > 2.6 mmol/L)
• body weight < 45 or > 90 kg
• admitted to intensive care unit before this admission within 3 months
• have diseases as follows: parathyroid disease, rickets, or liver cirrhosis - Child C
• diagnosed with renal stone, tuberculosis, or sarcoidosis
• Non-native speaker