Vitamin D3, which is a form of vitamin D, is found in small amounts in very few foods like egg yolks, fortified cereal or milk, beef liver and fatty fish like tuna, explains the National Institutes of Health's Office of Dietary Supplements. Because there are so few foods that contain vitamin D, a person may need to take supplements to ensure he is getting the daily recommended amount of this vitamin.
According to the NIH's Office of Dietary Supplements, the daily recommended amount of vitamin D for adults between the ages of 19 and 70 is 600 IU. Although there are two forms of vitamin D supplements sold on the market, which are vitamin D2 and vitamin D3, vitamin D3 is the one that people should opt for, reports Medscape. Vitamin D3 also is called cholecalciferol.
However, this vitamin supplement is not vegetarian because it is derived from an animal source, reports the Vitamin D Council. Another method to get vitamin D3 is through sun exposure. However, exposure to the sun's rays should not be excessive to avoid skin damage or skin cancer, suggests the Vitamin D Council.
Vitamin D is important for bones, nerves and muscles in the body. Not getting enough of this vitamin can cause bones to become brittle. Rickets and osteomalacia are two conditions associated with vitamin D deficiency, states NIH's Office of Dietary Supplements.