Vitamin D doses Daily oral dosing of vitamin D3 using 5000 TO 50,000 international units a day in long-term hospitalized patients: Insights from a seven year experience https://pubmed.ncbi.nlm.nih.gov/30611908/ Dayton and Cincinnati, Ohio Vitamin D3 is a hormone produced in the skin, in amounts estimated up to 25,000 international units (IUs) a day, by the action of UVB radiation Vitamin D deficiency is common, lack of adequate sun exposure to the skin, vitamin D is present in very few food sour