A 1,000 international unit dose of vitamin D is 25 micrograms, which converts to approximately 0.03 milligrams, according to Mayo Clinic. As of 2010, the recommended daily allowance of vitamin D is 600 international units for people ages 1 to 70 years or for women who are pregnant or breast-feeding.
Doctors often recommend higher doses of vitamin D to treat other conditions, according to Mayo Clinic. For example, for heart disease, the recommended dose is 200 to 2,000 international units, while doctors prescribe up to 9,000 international units of vitamin D to treat cognitive problems. Doctors recommend up to 50,000 international units of vitamin D weekly as a treatment for fertility, while some recommend up to 50,000 international units weekly for treating fibromyalgia.