Vitamin D is a fat-soluble vitamin that has many functions in the body. Getting plenty of vitamin D in your diet may help to prevent bone disorders and some types of cancer, according to the National Institutes of Health Office of Dietary Supplements. Some people are more at risk for becoming deficient in this vitamin than others, putting them at higher risk of osteoporosis and other health problems.
Vitamin D is found in all the cells in your body and helps to regulate calcium and phosphorus absorption, blood-sugar balance and insulin activity, blood pressure, muscle composition and immune system response. It is important in building strong bones, cell differentiation and muscle and nerve function.
Everyone up to age 50 should get 200 international units of vitamin D per day. If you are between 51 and 70, you need 400 IU, and those over 71 need 600 IU of vitamin D per day. Corticosteroids, weight-loss drugs, cholesterol-lowering drugs and some medications for controlling epileptic seizures can interfere with vitamin D absorption and function, so if you are taking these medications, you may need extra vitamin D.
If you have vitamin D deficiency, you may experience muscle pain or weakness. Children may get rickets, resulting in bowed limbs and stunted growth, and adults may get osteomalacia, a condition involving soft bones and bone pain, the Linus Pauling Institute explains. A deficiency of vitamin D also may weaken the immune system and cause fatigue, depression and impaired cognitive function.
Breastfed babies, people who don't spend much time in the sun without sunscreen, people with dark skin, older adults, obese individuals and those with disorders that impair their ability to properly process fat are more at risk for vitamin D deficiency. The body requires dietary fat in order to absorb vitamin D, so people who consume very low amounts of fat also may have low levels of vitamin D.
Eating plenty of foods rich in vitamin D or taking supplements containing vitamin D can help prevent vitamin D deficiency. Food sources include fortified milk, salmon, shrimp, cod, sardines and fortified cereals and juices. Spending a short time in the sun can provide vitamin D, as your body can synthesize this vitamin with sun exposure. However, those who live in latitudes above 40 degrees north or below 40 degrees south do not get sufficient ultraviolet-light exposure for synthesizing vitamin D from October or November through March, the Linus Pauling Institute notes.