* organ failure requiring admission to a resuscitation or high dependency unit * comorbidity that is life-threatening in the short-term (life expectancy \<3 months) * any reason that makes follow-up at day 28 impossible * vitamin d supplementation in the previous month, with the exception of treatment providing less than 800 iu of vitamin d per day * contraindication for vitamin d supplementation: active granulomatosis (sarcoidosis, tuberculosis, lymphoma), history of calcic lithiasis, known hypervitaminosis d or hypercalcemia, known intolerance to vitamin d * participation in another simultaneous trial * safeguard of justice * peripheral capillary oxygen saturation (spo2) ≤92% in spite of an oxygen therapy \> 5l/min

* organ failure requiring admission to a resuscitation or high dependency unit * comorbidity that is life-threatening in the short-term (life expectancy \<3 months) * any reason that makes follow-up at day 28 impossible * vitamin d supplementation in the previous month, with the exception of treatment providing less than 800 iu of vitamin d per day * contraindication for vitamin d supplementation: active granulomatosis (sarcoidosis, tuberculosis, lymphoma), history of calcic lithiasis, known hypervitaminosis d or hypercalcemia, known intolerance to vitamin d * participation in another simultaneous trial * safeguard of justice * peripheral capillary oxygen saturation (spo2) ≤92% in spite of an oxygen therapy \> 5l/min

- organ failure requiring admission to a resuscitation or high dependency unit - comorbidity that is life-threatening in the short-term (life expectancy <3 months) - any reason that makes follow-up at day 28 impossible - vitamin d supplementation in the previous month, with the exception of treatment providing less than 800 iu of vitamin d per day - contraindication for vitamin d supplementation: active granulomatosis (sarcoidosis, tuberculosis, lymphoma), history of calcic lithiasis, known hypervitaminosis d or hypercalcemia, known intolerance to vitamin d - participation in another simultaneous trial - safeguard of justice - peripheral capillary oxygen saturation (spo2) ≤92% in spite of an oxygen therapy > 5l/min

- organ failure requiring admission to a resuscitation or high dependency unit - comorbidity that is life-threatening in the short-term (life expectancy <3 months) - any reason that makes follow-up at day 28 impossible - vitamin d supplementation in the previous month, with the exception of treatment providing less than 800 iu of vitamin d per day - contraindication for vitamin d supplementation: active granulomatosis (sarcoidosis, tuberculosis, lymphoma), history of calcic lithiasis, known hypervitaminosis d or hypercalcemia, known intolerance to vitamin d - participation in another simultaneous trial - safeguard of justice - peripheral capillary oxygen saturation (spo2) ≤92% in spite of an oxygen therapy > 5l/min

- organ failure requiring admission to a resuscitation or high dependency unit - comorbidity that is life-threatening in the short-term (life expectancy <3 months) - any reason that makes follow-up at day 28 impossible - vitamin d supplementation in the previous month, with the exception of treatment providing less than 800 iu of vitamin d per day - contraindication for vitamin d supplementation: active granulomatosis (sarcoidosis, tuberculosis, lymphoma), history of calcic lithiasis, known hypervitaminosis d or hypercalcemia, known intolerance to vitamin d - participation in another simultaneous trial - persons deprived of their liberty by administrative or judicial decision, persons under psychiatric care under duress, adults subject to a legal protection measure - peripheral capillary oxygen saturation (spo2) ≤92% in spite of an oxygen therapy > 5l/min

- organ failure requiring admission to a resuscitation or high dependency unit - comorbidity that is life-threatening in the short-term (life expectancy <3 months) - any reason that makes follow-up at day 28 impossible - vitamin d supplementation in the previous month, with the exception of treatment providing less than 800 iu of vitamin d per day - contraindication for vitamin d supplementation: active granulomatosis (sarcoidosis, tuberculosis, lymphoma), history of calcic lithiasis, known hypervitaminosis d or hypercalcemia, known intolerance to vitamin d - participation in another simultaneous trial - persons deprived of their liberty by administrative or judicial decision, persons under psychiatric care under duress, adults subject to a legal protection measure - peripheral capillary oxygen saturation (spo2) ≤92% in spite of an oxygen therapy > 5l/min