Foods, dietary supplements and sun exposure provide vitamin D. Getting sufficient amounts -- 600 IU daily for most adults -- is vital for overall health. Your skeletal system requires vitamin D because the vitamin facilitates calcium absorption, a key for healthy bones and development. Your liver, not your bones, produces vitamin D in response to the sun's ultraviolet rays. Valuable food sources of this vitamin include cod liver oil, seafood, such as salmon and tuna, and fortified juices and dairy products. Eggs, margarine and fortified cereals contain moderate amounts.