Your body needs vitamin D to absorb calcium (which, of course, helps keep your bones healthy). For adults ages 19 to 70, the RDA of vitamin D is 600 international units (IUs) a day. The recommendation increases to 800 IUs a day for adults age 71 and older. Good sources of vitamin D include oily fish, such as tuna and sardines, egg yolks and fortified milk. Sunlight also contributes to the body's production of vitamin D. If you're worried about getting enough vitamin D, ask your doctor about supplements.