Vitamin D has an important job in keeping the immune system regular. It helps to prevent autoimmune diseases such as inflammatory bowel disease, as cited by Margherita Cantora and colleagues in December 2004 in "The American Journal of Nutrition." Vitamin D deficiency is not only linked to outcomes like immune system-related diseases; it is also progressed by the diseases themselves, thereby making the condition worse.
The prevailing knowledge of vitamin D has been that it helps maintain the balance of calcium, which helps bone formation and calcium absorption within the bones, according to Cantora and colleagues. Vitamin D works with T cells, the body's natural killer cells, to fight off infection and disease, according to Eva Wintergerst in 2007 in the "Annals of Nutrition and Metabolism." When a person does not have enough T cells, they are more likely to become sick and die, because the immune system then has a reduced ability to fight pathogens outside of cell bodies, as Wintergerst explains. The process becomes a downward spiral, because once an infection sets in, it further reduces the amount of vitamin D available.
Vitamin D has been useful in treatments aimed at restoring immune system function. Some immune system-related diseases, like ulcerative colitis and Crohn's disease, have been linked to vitamin D deficiencies and successfully treated with vitamin D supplementation, according to Cantora and colleagues. Yet other immune system-mediated diseases such as asthma and those caused by infectious organisms are not remedied by vitamin D treatment, according to Cantora and colleagues.
Having conditions such as inflammatory bowel disease leads to vitamin D deficiencies. This is even more so in people with Chron's disease, likely due to the fact that they have absorption issues within the intestines, as Cantora and colleagues explain. Also, the drug used to treat inflammatory bowel disease leads to bone loss. Researchers believe that vitamin D deficiency is caused by the drug, as noted by Cantora and colleagues. Being pregnant, having an eating disorder, and chronic alcohol consumption can all affect the amount of vitamin D present for use by the body. The elderly are at an elevated risk as well, since, with aging, the immune system becomes weaker with a decreased ability to fight infections, according to Wintergerst.
The sun is a major source for vitamin D production. The skin has reactions sparked by sunlight that allow for this process to occur. Vitamin D can also be found in foods like cheese, milk and fish. Yet, there are not as many vitamin D-rich foods compared to that of other types of nutrients, as discussed by Cantora and colleagues.
People who live in northern climates are particularly at risk for vitamin D deficiency, according to Cantora and colleagues. This risk is heightened during the winter months. The fact that vitamin D is not as readily available from foods as other nutrients makes where a person lives on the Earth a consideration of vitamin D intake, since so much of that can be dependent on sun exposure.