The recommended daily allowance for vitamin D is 400 international units for infants and 600 to 800 international units for older individuals. Good sources of vitamin D include fatty fish such as salmon and tuna, fish liver oils and fortified foods such as milk, notes the National Institutes of Health.
Vitamin D intake for most Americans comes from fortified foods. In the United States, all infant formulas are mandated to contain 40 to 100 international units of vitamin D per kilocalorie, while milk is typically voluntarily fortified with 100 international units per cup. Other vitamin D fortified foods include breakfast cereals and some brands of orange juice, yogurt and margarine, explains the National Institutes of Health.