Avoiding direct sunlight and eating a diet containing insufficient amounts of vitamin D can lead to vitamin D deficiency, according to WebMD. Illnesses that damage the ability of the intestine to absorb vitamin D, such as celiac disease, cystic fibrosis and Crohn's disease, can also lead to vitamin D deficiency. Because fat cells extract vitamin D from the blood, people who are obese often have a vitamin D deficiency.
The body produces vitamin D in response to sunlight exposure, and vitamin D is present in foods such as egg yolks, certain fish, fortified cereals and dairy products. People who eat strict vegan diets are particularly susceptible to vitamin D deficiency.
Getting 10 to 15 minutes of direct sunlight three times per week causes the body to produce sufficient amounts of vitamin D, states MedlinePlus. The sun needs to shine on the face, back, arms or legs without sunscreen. Sunshine through windows does not cause the body to produce vitamin D, and people with darker-colored skin often produce less vitamin D as a result of sun exposure.
Fatty fish, such as salmon, tuna and mackerel, contain high amounts of vitamin D, and egg yolks, beef liver and cheese contain small amounts of vitamin D, notes MedlinePlus. Milk sold in the United States typically contains 400 International Units of vitamin D for each quart.
Vitamin D assists the body in utilizing calcium and is crucial for strong, healthy bones, explains WebMD. Health risks associated with low levels of calcium in the blood include bone pain, muscle weakness, cancer, cardiovascular disease and cognitive impairment in seniors.