Are there scientific studies showing that vitamin D exerts any short- or long-term effects (positive or negative) on autoimmune conditions?
For the past two decades researchers have known that nearly every cell in the human body possesses vitamin D receptors (VDRs). The VDRs in immune cells have attracted a great deal of scientific interest, but their actions are still not completely understood. Vitamin D seems to enhance innate immune responses (those that are directed against unfamiliar agents) while it suppresses autoimmune responses (those that target our own tissues as if they were foreign invaders). However, there is some question of whether vitamin D deficiencies are the cause or result of autoimmune disease.
A 2001 Lancet study suggested that individuals who consume more vitamin D are less likely to develop type 1 diabetes, and the Iowa Women’s Health Study, which involved nearly 30,000 women, revealed that the risk for developing rheumatoid arthritis increased as vitamin D intake decreased. Similarly, a study published in the December 2006 issue of The Journal of the American Medical Association demonstrated that higher serum 25-hydroxyvitamin D levels were associated with a lower risk for multiple sclerosis. Unfortunately, more recent studies have suggested that vitamin D supplementation may exacerbate autoimmune conditions. Clearly, more research is needed.
The link between vitamin D and autoimmunity – while unclear at this time – is a compelling one. Although it has not yet been proven that vitamin D treatment changes the course of any autoimmune disease, ongoing research may establish vitamin D’s role as a therapeutic agent for a number of connective tissue disorders.
What is the optimal dosage of Vitamin D?
Studies show that many individuals – even in developed countries – are vitamin D deficient. In response to this finding, the Institute of Medicine recently revised its recommendations for vitamin D intake: the RDA now ranges from 400 to 800 IU daily, depending on your age and pregnancy status, and the tolerable upper intake level (TUIL) for adults has been increased to 4,000 IU daily.
However, several experts, such as Dr. Reinhold Vieth at the University of Toronto and Dr. Michael Holick at Boston University, feel these guidelines are still too conservative. Vitamin D toxicity, they say, is unlikely at daily intakes up to 10,000 IU, and most people should get 1,000 to 2,000 IU daily. Still, individuals with specific disorders – sarcoidosis, for example – may need to limit their vitamin D intake to avoid toxicity.
What form of vitamin D (pills, milk, sun) is preferred for best absorption? If I take pill form, does it matter whether it is bone or vegetable source derived?
There’s no question that exposure to ultraviolet light is the quickest and most efficient way to get vitamin D into your circulation. However, since most Americans don’t get enough sun to produce sufficient vitamin D for their needs, and since most foods offer low biovailability (the percentage of supplied vitamins in foods that are actually available to the body for use), supplementation is recommended for the majority of individuals. While there is some debate about the best vehicle for supplementing vitamin D, most experts agree that animal-derived vitamin D3 – the form produced in your skin when it absorbs ultraviolet light – is superior to plant-derived vitamin D2. For people who wish to avoid animal products, though, D2 is an acceptable source.
Questions for your doctor:
- Given the current state of my health, should I get my vitamin D level checked?
- Is there any reason I shouldn’t take a vitamin D supplement?
- Would my autoimmune condition respond to high-dose vitamin D therapy?
Hypponen E, et al. Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study. Lancet 2001;358(9292):1500-1503
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
Munger K, et al. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. The Journal of American Medicine Association 2006;296(23):2832-2838
R Vieth. Critique of the Considerations for Establishing the Tolerable Upper Intake Level for Vitamin D: Critical Need for Revision Upwards. Journal of Nutrition. 2006;136(4):1117-1122
Holick M. Deficiency of sunlight and vitamin D. BMJ. 2008;336(7657):1318-1319