As of 2010, the recommended daily allowance of vitamin D for adults ages 18 to 70 is 600 international units, according to Mayo Clinic. People can attain an ideal vitamin D blood content of 20 nanograms per milliliter through daily exposure to sunlight.
Most multivitamins in the form of tablets, liquids or capsules contain 50 to 100 IU of vitamin D, states Mayo Clinic. Patients may take vitamin D alone in higher strengths for eczema, heart disease, cognition, cystic fibrosis, fall prevention and other medical reasons. To prevent certain types of cancers, Mayo Clinic advises 400 to 1,100 IU of vitamin D.