Autoimmunity is a wide-spread condition covering a range of diseases and plaguing more than 50 million people in the United States alone. Because of its wide reach and diverse pathology, there is much about autoimmunity that we do not know. The role of vitamin D in autoimmunity’s pathology and treatment is still a relatively unexplored topic for study, but the links that are understood are promising.
What Is Autoimmunity?
Autoimmunity occurs when the body treats its own tissues or organs like foreign agents and attacks them. Most cells have unique identifiers that protrude from their surface. The body identifies these antigens as either friend or foe, either letting the cells go about their work or initiating the immune response to destroy them.
In cases of autoimmunity, the body marks its own antigens as hostile and initiates an immune response to take out the threat. One such example is type 1 diabetes, a condition in which the immune system targets and destroys pancreatic cells that produce insulin. Other examples of autoimmune diseases include rheumatoid arthritis, Crohn’s disease, systemic lupus erythematosus, and multiple sclerosis.
The symptoms and side effects of autoimmunity vary depending on which cells are targeted, but tissue damage, inflammation, and loss of functionality in affected organs or joints are common. Unfortunately, incidents of autoimmunity seem to be on the rise among Western countries. The need to better understand the role of vitamin D in autoimmunity, therefore, grows ever more pressing.
Understanding Vitamin D
Sometimes called the sunshine vitamin, vitamin D is a fat-soluble vitamin that the body produces endogenously when the skin is exposed to ultraviolet (UV) rays, usually in the form of sunlight. It can also be ingested, and while vitamin D is naturally present in a few foods, it is more commonly added or taken supplementally.
The role of vitamin D in many of the body’s vital processes cannot be understated. It is most commonly associated with regulating calcium homeostasis by promoting calcium absorption in the intestine. Additionally, it is essential for normal bone mineralization. When levels of the active form of vitamin D (generally made in the liver) are low, calcium is mobilized to the bone rather than the intestines. Once there, it facilitates correct bone growth and remodeling.
Without sufficient levels of vitamin D, bones can become brittle, thin, or even misshapen. This is the case with diseases such as rickets and osteomalacia. Monitoring calcium levels has the additional benefit of reducing inflammation, preventing hypocalcemic tetany (the involuntary cramping or spasming of muscles), modulating cell growth and the metabolism of glucose, neuromuscular function.
The Role of Vitamin D in Autoimmunity
In addition to the other roles already listed, it becomes increasingly clear that vitamin D plays an important part in the modulation of the body’s immune system. In addition to poor bone health, deficiency of vitamin D has been linked to cardiovascular diseases, cancer, and autoimmune diseases. In fact, there is a high prevalence of vitamin D deficiency in patients suffering from autoimmunity.
While not serving as conclusive evidence for causation, this fact is enough to warrant further examination between autoimmunity pathology and vitamin D levels, as is the fact that virtually all immune cells express a cell receptor for vitamin D. A study published in 2017 titled “Vitamin D in Autoimmunity: Molecular Mechanisms and Therapeutic Potential” explored the role of vitamin D in autoimmunity by comprehensively reviewing the available data. Authors Dankers, et al. concluded that the body of evidence indicates vitamin D should be included in treatment and prevention methods for autoimmune conditions.
The Mechanism of Vitamin D
Receptors for vitamin D receptors are found on nearly all immune cells, including blood lymphocytes. These receptors serve as binding sites for vitamin D to dock and modulate immune cell behavior. In this way, vitamin D plays a clear role in influencing and mediating the immune response.
This fact is well-known. In fact, before antibiotics were discovered, vitamin D was used to treat mycobacterial infections such as tuberculosis. However, this mediation is only possible when the active form of vitamin D binds to a nuclear receptor and initiates its signaling cascade. The inactive precursor form of vitamin D, 25(OH)D3, is ineffectual in the process and must first be converted.
Though it was originally thought that this conversion process could only take place in the liver, more recent evidence indicates that cells associated with the immune response (macrophages, monocytes, dendritic cells, B cells, and T cells) can also affect the conversion. This ability to build up vitamin D levels at the site of inflammation highlights the role of vitamin D in the immune system and indicates its vitality in staving off the ill effects of autoimmunity.
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