Some foods that contain vitamin D include fortified dairy products, fatty fish, fortified juices and egg yolks. Cod liver oil contains high levels of vitamin D, and the vitamin is also added to some ready-to-eat cereals.
Vitamin D is made naturally in the body when the skin is exposed to sunlight. Sunscreen and clothing can block the sun from reaching the skin, inhibiting the natural production of vitamin D. Cloud cover and smog can also keep sunlight from reaching the skin in sufficient amounts for vitamin D production, and the angle of the sun in northern latitudes reduces vitamin D production in the winter months. Individuals who do not get much sun exposure usually need to get extra vitamin D from food or supplements. Multivitamins typically contain vitamin D in amounts ranging from 400 to 1,000 IU. Separate vitamin D supplements are also available.
The recommended daily intake of vitamin D for most teenagers and adults is 600 IU per day, according to guidelines released in 2010 by the Institute of Medicine's Food and Nutrition Board. Children under age 12 need just 400 IU per day, while elderly individuals over 70 need 800 IU per day. People who do not get enough vitamin D may develop rickets or osteomalacia, both of which affect the bones.