Vitamin D is most famous for its contribution to joint and bone health by helping the body absorb calcium. It has been shown that people who take in enough vitamin D are less likely to suffer from osteoporosis and joint pain. This vitamin can also slow the affects of arthritis and lessen back pain in many individuals. Studies have shown that vitamin D can also prevent certain types of cancer.

Vitamin D is one of the only vitamins produced naturally by the body. However, in order for the body to produce vitamin D, it has to be exposed to an adequate amount of sunlight. Generally, an hour per week is more than enough, but surprisingly, many people are still not exposed to enough sun to produce beneficial amounts of vitamin D. Also, studies have shown that as we age, we tend to produce less vitamin D even with adequate sun exposure. These are the primary reasons why many adults have to monitor their diets to make sure they are taking in enough vitamin D.

While it is important to have enough vitamin D in your diet, it is possible to take in too much vitamin D. This often happens when a person receives a good amount of sun exposure and consumes many foods that contain moderate amounts of vitamin D, but also continues to take a vitamin D supplement. For this reason, it is important to discuss with your doctor whether or not you require a vitamin D supplement as part of your diet.

Individuals who have reduced ability to absorb dietary fat (fat malabsorption) may need extra vitamin D because it is a fat soluble vitamin. Some causes of fat malabsorption are pancreatic enzyme deficiency, Crohn's disease, cystic fibrosis, sprue, liver disease, surgical removal of part or all of the stomach, and small bowel disease. Symptoms of fat malabsorption include diarrhea and greasy stools.

Vitamin D supplements are often recommended for exclusively breast-fed infants because human milk may not contain adequate vitamin D. The Institute of Medicine states that "With habitual small doses of sunshine, breast-fed or formula-fed infants do not require supplemental vitamin D." Mothers of infants who are exclusively breastfed and have a limited sun exposure should consult with a pediatrician on this issue. Since infant formulas are routinely fortified with vitamin D, formula fed infants usually have adequate dietary intake of vitamin D.