Everyone knows that vitamin D prevents rickets. Increasingly, scientists are learning of its role in regulating immunity and preventing some forms of cancer.
For more than 20 years scientists have known that vitamin D, a vitamin best known for its effects on calcium metabolism and bone mineralization, is also involved in modulating the activity of human immune cells.
In most respects, vitamin D’s influence on the immune system is suppressive. Notably, its effects are potent enough to warrant consideration of this vitamin as a therapeutic agent for managing some immune-mediated illnesses. (Griffin M, Xing N, Kumar R. Vitamin D and its analogs as regulators of immune activation and antigen presentation. Annu Rev Nutr 2003;23:117-45)
Mechanism of Action of Vitamin D
- Like most of vitamin D’s biological effects, its actions within immune cells are mediated by an intra-nuclear transcription factor known as the vitamin D receptor (VDR). When the active form of vitamin D enters the nucleus of a cell and binds to the VDR, it initiates a cascade of events that culminates in the transcription of specific genes. The products of gene transcription are the proteins, enzymes, and hormones that are necessary for life. (Sutton A, MacDonald P. Vitamin D: more than a “bone-a-fide” hormone. Mol Endocrinol 2003;17(5):777-91 and Guyton K, et al. Vitamin D and vitamin D analogs as cancer chemopreventive agents. Nutr Rev 2003;61(7):227-38
- An increasing body of evidence points to vitamin D’s role in enhancing innate immune responses—those that are targeted toward unfamiliar or novel antigens—and in down-regulating those immune responses that lead to autoimmunity—those that target our own tissues as if they were foreign invaders.
Cancer and Vitamin D
- Some epidemiological studies support the notion that vitamin D, in adequate doses, may play an important role in preventing cancers of the colon, breast and prostate. While such studies cannot prove an association between vitamin D intake and cancer incidence, the suggestion is certainly intriguing. (McCullough M, et al. Calcium, vitamin D, dairy products, and risk of colorectal cancer in the Cancer Prevention Study II Nutrition Cohort (US). Cancer Causes Control 2003;14(1):1-12; Feskanich D, et al. Plasma vitamin D metabolite and risk of colorectal cancer in women. Cancer Epidemiol Biomarkers Prev 2004;13(9):1502-08; Lowe L, et al. Plasma 25-hydroxy vitamin D concentrations, vitamin D receptor genotype and breast cancer risk in a UK Caucasian population. Eur J Cancer 2005;41(8):1164-1169; Bertone-Johnson E, et al. Plasma 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D and risk of breast cancer. Cancer Epidemiol Biomarkers Prev 2005;14(8):1991-97; Ahonen M, et al. Prostate cancer risk and prediagnostic serum 25-hydroxyvitamin D levels. (Finland). Cancer Causes Control 2000;11(9):847-852)
Autoimmunity and Vitamin D
- Among autoimmune diseases, it is interesting to note that as latitude increases, so does the prevalence of multiple sclerosis, rheumatoid arthritis, and type 1 diabetes. This suggests an association between lower exposure to sunlight (decreased vitamin D synthesis) and autoimmunity.
- Although other factors could explain this association, both animal and human observational studies show that vitamin D may, indeed, play an important role in preventing several autoimmune diseases. (Hypponen E, et al. Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study. Lancet 2001;358(9292):1500-03; Munger K, et al. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. JAMA 2006;296(23):2832-38; Merlino L, et al. Vitamin D intake is inversely associated with rheumatoid arthritis: results from the Iowa Women’s Health Study. Arthritis Rheum 2004;50(1):72-77)
Vitamin D toxicity is very unlikely at doses below 10,000 IU daily. The current daily upper limit recommended by the Food and Nutrition Board of the Institute of Medicine is 2,000 IU (50 mcg). This recommendation may be overly conservative.
The copyright of the article Vitamin D and Immunity in Vitamins & Minerals is owned by Stephen Allen Christensen. Permission to republish Vitamin D and Immunity in print or online must be granted by the author in writing.
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