From Arthritis to Zoster

Everyone knows that vitamin D – often called the “sunshine” vitamin – is vital for calcium metabolism and the development of strong bones. What has become clearer in the past few years is that vitamin D is also essential for normal immune function.

Vitamin D exerts its effects by binding to a nuclear receptor that is present in many of our cells. This vitamin D receptor (VDR) regulates the activity of at least 50 human genes, some of which are responsible for optimal immune activity.

T cells and antigen-presenting cells (macrophages, dendritic cells, etc.) express the vitamin D receptor; some macrophages also possess the enzyme that converts 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D (the vitamin’s active form). VDR-dependent stimulation of immune cells promotes a variety of cellular functions: antigen processing, cytokine production, cellular differentiation and division, production of antimicrobial peptides, and antibody production are all influenced by vitamin D.

Additionally, vitamin D exerts a suppressive effect on cellular division while simultaneously encouraging cellular differentiation in many tissues. These two activities help to prevent the proliferation of undifferentiated cells – in other words, vitamin D helps to inhibit the development of cancers. Epidemiologic surveys have demonstrated a strong link between low serum levels of vitamin D and cancers of the colon, breast, prostate and skin.

Because vitamin D helps to control immune-mediated inflammation, it may also inhibit those processes that lead to autoimmunity. Deficiency of vitamin D has been linked to several autoimmune diseases, including Sjögren’s syndrome, Crohn’s disease, multiple sclerosis, rheumatoid arthritis, and thyroiditis. Interestingly, vitamin D deficiency has been misdiagnosed as chronic fatigue, fibromyalgia, and peripheral neuropathy.

It should be noted that vitamin D appears to be a selective immune modulator—that is, not all immune-mediated conditions are positively affected by supplementation, because not all immune problems are related to vitamin D deficiency. Scientists are helping to unravel some of vitamin D’s immunologic functions, but research in this area is just beginning.

Current recommendations for daily allowances of vitamin D (400 IU for adults) are probably on the low side, particularly since this nutrient is not found in abundance in many foods. 20 minutes of exposure to sunlight every day will confer adequate vitamin D production, but many people wish to avoid sunlight – along with its risks for skin cancer and solar elastosis – and adequate exposure is difficult for people who work indoors or who live at higher latitudes. Hence, for many individuals supplementation is the key to avoiding deficiency. Total doses should not exceed 2,000 IU daily, and vitamin D3 (cholecalciferol) has been shown to be more effective than D2 (ergocalciferol) in humans.

Simply taking a vitamin D supplement, however, is not sufficient to reap its full benefits. Adequate intake of calcium (1200 – 1500 mg daily) and magnesium (500 – 600 mg daily) is necessary to help vitamin D perform optimally. Phosphorus is also important, but this mineral is present in adequate amounts in the typical American diet. Chelated forms of minerals – those that are “hooked” to an amino acid – are usually better absorbed than the more commonly used (and cheaper) supplements on the market.