The recommended daily allowance of vitamin D is 600 international units for adults under 70 years of age and 800 international units for adults 71 and older, according Mayo Clinic. The recommended dose of vitamin D for pregnant women is 600 international units, but some doctors recommend much higher levels.
A daily dose of vitamin D for people with ailments such as cystic fibrosis and multiple sclerosis increases up to 10,000 international units, according to Mayo Clinic. Direct sun exposure, fortified foods and supplements offer the greatest percentage of vitamin D, explains the National Institutes of Health. Fatty fish, such as mackerel, salmon and tuna, provide the highest amount of vitamin D of all naturally occurring food.