As of 2015, the recommended dose of vitamin D is 600 international units for adults from ages 18 to 70, according to Mayo Clinic. Individuals over the age of 71 should take 700 international units of vitamin D.
The recommended dose of vitamin D can vary based on the conditions being treated. For instance, vitamin D is used to prevent cancer in doses from 400 to 1,100 international units. It's also used to improve fertility and is taken in doses from 400 to 50,000 international units every one to two weeks. People taking vitamin D should speak to their doctors to determine the right dosage based on their personal health goals.