Despite its name, Vitamin D is not a vitamin. It is a steroid hormone necessary by our body to regulate at least 229 of our genes and thousands of functions in our cells, including the cells of our immune system. Vitamin D is found in small quantities in food and is primarily produced by the skin when exposed to sunlight. This sun exposure is affected by many factors, such as time of day, the use of sunscreens and geographic location. It has been correlated that areas further from the equator have increased incidence of autoimmune conditions, specifically multiple sclerosis.

A physiological, safe dose of Vitamin D is approximately 10,000 IU/day. This is the amount our own body produces when exposed to 20-30 minutes of the mid-day sun. With this daily dose, no precautions or medical supervision is necessary. It is worth noting that the IOM (Institute of Medicine) indicates that 10,000 IU/day is considered the "NOAEL"- No Observed Adverse Effect Level.

With adequate levels of Vitamin D, essential cellular processes will work properly; however, the majority of patients with Autoimmune Diseases have an increased resistance to the effects of Vitamin D. This resistance is mostly due to genetic polymorphisms and may also be influenced by factors such as body weight, body mass index, and age. Consequently, patients with Autoimmune Disorders require higher levels of Vitamin D to overcome this resistance and unlock the beneficial effects of this important substance at the cellular level.

The main role of Vitamin D is to regulate immune system activity. When there is a deficiency of vitamin D, the immune system is defective in protecting against viral/bacterial/fungal infections. This deficiency can also allow the immune system to dysregulate and attack its own body’s cells and tissues.

Vitamin D suppresses autoimmunity by downregulating Lymphocyte Th17 , which is the main immune cell involved in autoimmune processes. A dysregulation of Th17 causes overproduction of an "immune messenger" (cytokine) called interleukin 17. Production of interleukin 17 is a natural phenomenon and is necessary for a normal function of immune reactions but in adequate levels. In the autoimmune diseases, there is an overproduction of interleukin 17 due to an aberrant Th17 activity, and Vitamin D is the natural hormone that controls and modulates Th17 activity.

It is also important to mention that Vitamin D does not suppress the immune system; quite the contrary, it empowers the immune system against viruses, bacteria and other microorganisms.

The correction of Vitamin D deficiency in Autoimmune Diseases is a therapeutic approach based on scientific evidence. Studies have shown that Vitamin D, in addition to the known role in calcium homeostasis, has numerous actions in the body, with major interventions in the immune system.
There are thousands of scientific, peer-reviews studies that show the relationship between multiple sclerosis and Vitamin D3 deficiency, as well as the benefits of Vitamin D supplementation for patients with such conditions.

Let's take a look at a few examples:
In 2009, a study presented at the annual meeting of the  American Academy of Neurology found that high doses of Vitamin D dramatically cut the relapse rate in people with multiple sclerosis. Patients in the high-dose group were given escalating doses of vitamin D for six months, to a maximum of 40,000 IU daily. Doses were gradually lowered over the next six months, averaging out to 14,000 IU daily for the year. The patients given high-dose vitamin D in the study had a lower relapse rate, and their T cell activity dropped significantly, when compared to the group who took lower doses.

Burton, Jodie. “Is Vitamin D a Ray of Hope for Patients With MS?” Neurology Reviews 7;17.7 (2009) 1-16.

In 2011, a study conducted in 209 patients of systemic lupus erythematous at the Ohio State University Medical Center found that the majority of patients included in the study had Vitamin D deficiency. The authors concluded that Vitamin D levels were negatively correlated with lupus disease activity. In other words, the more Vitamin D in the blood, the lower was the lupus disease activity, and vice versa.

Rovin, Brad H.; Vitamin D Deficiency As Marker for Disease Activity and Organ Damage in Systemic Lupus Erythematosus:  [abstract]. Arthritis Rheum 2011;63 Suppl 10 :2276.

 In 2013, a study supervised by Dr. Coimbra assessed the effect of prolonged administration of high-dose Vitamin D on the clinical course of vitiligo and psoriasis. In this study, nine patients with psoriasis and 16 patients with vitiligo received 35,000 IU daily for six months in association with a lowcalcium diet and hydration (minimum 2.5 L daily). The clinical condition of patients significantly improved during the treatment, with no signs of toxicity. The results of the trial suggest that, at least for patients with Autoimmune Disorders like vitiligo and psoriasis, a daily dose of 35,000 IU of vitamin D is a safe and effective therapeutic approach to reducing disease activity.

Finamor, Danilo C; Coimbra.“A pilot study assessing the effect of prolonged administration of high daily doses of vitamin D on the clinical course of vitiligo and psoriasis.” Dermato-Endocrinology 5.1 (2013): 222–234.

In 2015, a study published in PLOS Medicine demonstrated a genetic correlation suggesting that lack of Vitamin D may be a cause of multiple sclerosis. Using a technique called Mendelian randomisation, the authors examined 14,498 people with multiple sclerosis and 24,091 healthy controls. The study concluded that a genetically lowered Vitamin D level is strongly associated with increased susceptibility to multiple sclerosis. According to Dr. Benjamin Jacobs, “This study reveals important new evidence of a link between Vitamin D deficiency and multiple sclerosis. The results show that if a baby is born with genes associated with Vitamin D deficiency they are twice as likely as other babies to develop MS as an adult. This could be because Vitamin D deficiency causes multiple sclerosis.”

Mokry, Lauren E.; Ross, Stephanie; Ahmad, Omar S.; Forgetta, Vincenzo; Smith, George D.; Leong, Aaron; Greenwood, Celia M.
T.; Thanassoulis, George; Richards, J. Brent. “Vitamin D and Risk of Multiple Sclerosis: A Mendelian Randomization Study.” PLOS Journal, 25 Aug. 2015. DOI: 10.1371/journal.pmed.1001866.

 In 2015, a study published by the MS Society Cambridge Centre for Myelin Repair, demonstrated the important role of Vitamin D in myelin repair. Researchers identified that the Vitamin D receptor protein pairs with an existing protein, called the RXR gamma receptor, already known to be involved in the repair of myelin. By adding Vitamin D to brain stem cells where the proteins were present, they found the production rate of oligodendrocytes (myelin making cells) increased by 80 percent. ,

Kohlhaas, Susan. “Vitamin D could repair nerve damage in multiple sclerosis, ” University of Cambridge. 07 Dec. 2015.

Not only patients with Multiple Sclerosis benefit from Vitamin D modulating therapy but so do most of the other common Autoimmune Diseases such as Rheumatoid Arthritis, Lupus, Psoriasis, Crohn's Disease, among others.

The possible side effects of taking high doses of Vitamin D for extended periods of time are an excess of calcium - in the blood (hypercalcemia) or in the urine (hypercalciuria), and loss of bone mass. Excess calcium can be easily avoided with a diet free of dairy and calcium-enriched foods, and regular lab tests to ensure calcium levels are kept under control. To avoid loss of bones mass, patients on the protocol are instructed to practice a daily routine of aerobic exercises, like a 30 minute fast walk. Those who cannot practice aerobic exercises might need medication with time, such as bisphosphonates, to prevent osteoporosis.