As we know it, Vitamin D is a fat-soluble vitamin used by the body for bone development and regulating calcium, magnesium and phosphate.
However, epidemiological studies and clinical trials provide evidence of a protective role of vitamin D in Autoimmune conditions. Vitamin D supplementation for Autoimmunity is becoming common practice.
Populations with low vitamin D levels (i.e., those living furthest from the equator and with high melanin levels in the skin) are identified as more likely to develop immune-mediated diseases.
In humans, the main source of vitamin D (approx. 90%) is exposure to UV sunlight where it is synthesised through the skin. Only approx. 10% is obtained through our diet. Vitamin D-rich foods include: cod liver oil, oily fish (salmon, sardines etc), eggs, dairy products, certain mushrooms, some meat and fortified foods.
Vitamin D includes both vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). Vitamin D3 is made in the skin under the influence of UV light. Vitamin D2 is derived from the plant sterol ergosterol (e.g. found in mushrooms).
To be used by the body, vitamin D must be metabolised in the liver to 25-hydroxyvitamin D (25-OH-D3) and then carried to the kidneys, where it is transformed into the fully active form 1,25-dihydroxyvitamin D (1,25-(OH)2D). Any physiological dysregulation or gene variations in these processes could impair an individual's ability to metabolise vitamin D efficiently.
The circulating concentration of 25(OH)D is currently accepted as the best marker of vitamin D status. A level greater than 30 ng/mL is required to maintain a healthy level of vitamin D. The 1,25-(OH)2D active form is what binds to a vitamin D receptor (VDR) in the cell and activates gene expression. Research indicates VDR's are expressed in almost all human cells and tissues, as well as most immune cells. This emphasises how important vitamin D is to nearly every cell and function in the human body. Vitamin D deficiency is often reported in chronic conditions associated with increased inflammation and deregulation of the immune system, such as diabetes and rheumatoid arthritis.
It has also been found that many of the immune cells such as macrophages and dendritic cells, are capable of biologically synthesising active vitamin D from circulating 25-OH-D3. This is critical for the innate and adaptive immune system response at the local site of inflammation and further supports the immune modulating benefits of vitamin D.
Some direct and indirect effects of Vitamin D on the immune system in Autoimmunity include:
Regulates the balance of T-Regulatory cells and TH17 cells which are often imbalanced in Autoimmunity.
Promotes an anti-inflammatory environment, important in Autoimmunity, where chronic inflammation is often present.
Develops a synergistic association with the microbiome which has immune regulation capabilities in Autoimmunity.
Inhibits the production of pro-inflammatory cytokines implicated in Autoimmunity.
Suppresses T and B cell proliferation which are often underlying Autoimmune conditions.
The scientific evidence for vitamin D in regulating the immune system and calming Autoimmunity continues to stack up. It is important to get adequate, safe, sun exposure (especially in the winter months), to prevent vitamin D deficiency. Factors that can affect the efficiency of vitamin D synthesis from the sun include: skin colour (melanin content), weather, season, time of day, latitude, altitude, clothing, body surface area exposed, use of sunscreen, and skin type (e.g., ageing decreases synthesis of vitamin D in the skin). Therefore, individuals must consider their own personal circumstances when deciding on how much sun exposure is suitable.
Supplementation of vitamin D3 may be required through the year, especially if you have an Autoimmune condition. 10 micrograms (µg) or 400 international units (IU) of vitamin D is the safe recommended daily amount for adults. However, those with Autoimmune conditions may require different dosages depending on how deficient they may be. Regular vitamin D testing through your GP or through working with a registered nutritionist is highly recommended if you have an Autoimmune condition or if Autoimmunity runs in your family.
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