Inclusion Criteria:  newly admitted (within 24 hours) over eighteen, able to receive medication orally or through nasogastric tube expected to stay more than 72 hours in ICU given consent  Exclusion Criteria:  lack of patient's or relatives' consent expected short life or ICU stay (<48 hours) sepsis at admission kidney, liver or intestinal disease hypercalcemia (total calcium>10.6 mg/dL) history of a disorder associated with hypercalcemia (i.e., cancer, tuberculosis, sarcoidosis, hyperparathyroidism, nephrolithiasis) treatment with immunotherapy or vitamin supplements within one year pregnant or breastfeeding women discharge from ICU or death within 72 hours of admission