Food enriched with vitamin D include infant formula and cow's milk, In addition, some brands of orange juice, cereal, soy and almond milk, yogurt and margarine are also fortified with vitamin D. In general, one cup of milk has 100 International Units of the nutrient.
Products are fortified with vitamin D because it does not appear naturally in many foods. Fatty fish, such as salmon and tuna, and fish liver oils are excellent natural sources of vitamin D. A limited amount of the vitamin is also in beef liver, cheese, egg yolks and certain mushrooms. Most Americans get their vitamin D when it has been added to foods.
The ultraviolet radiation of sunlight also helps provide vitamin D. In the presence of sunlight, the body makes the vitamin. The amount manufactured depends upon the season, time and length of day, cloud cover, smog, skin melanin content and sunscreen usage.
One of the most important jobs of vitamin D is to help the body absorb calcium. This promotes healthy bone growth. During the 1930s, companies began adding vitamin D to milk to combat rickets. The program was highly effective.
Rickets causes bones to soften and become deformed. It also leads to bone breaks, teeth deformities, muscle cramps and poor muscle tone. In addition, bones do not grow well, so children with rickets sometimes do not grow taller than 5 feet.