Vitamin D Benefits for your immune system
Among all vitamin D benefits, the most widespread is it's role in disease prevention. Vitamin D essentially acts as a tonic for the immune system: it assists immune system cells in doing their job, and reels in cells that are a little out of control. In this article, we'll explain what's going on here, but first let's get some facts about vitamin D and disease prevention.
Vitamin D Benefits: What the case studies say
We'll get to cancer in the next article, but for now, let's just consider autoimmune diseases like diabetes, multiple sclerosis, arthritis, high blood pressure, and inflammatory bowel disease. First, a number of studies showed hints of how the vitamin D benefits that come from living at sun-baked latitudes lowered a variety of disease risks (1,2). Those findings inspired greater scrutiny into the role of this sun-derived hormone in fighting disease.
In one of the larger studies, a collection of serum samples from US Military personnel was used to compare vitamin D levels with the risk of developing multiple sclerosis (MS). Interestingly, low vitamin D levels strongly correlated with disease risk in white, but Hispanic or black patient populations did not experience these vitamin D benefits (3).
For diabetes, animal models show a strong connection between vitamin D levels and blood glucose and insulin levels (4). These finding are translated most clearly into human subjects in a study where Finnish children starting at 1 year old received 2000 IU/day of vitamin D benefits with reduced risk of getting type I diabetes by over 80% (5).
A similar story is repeated in the case of Crohn's disease and inflammatory bowel disease. In 1991, a study came out suggesting that these diseases were more common in the northern US and in urban areas than in the South (6). Over ten years later, a Norwegian study found a correlation between lower circulating 25-hydroxy vitamin D and Crohn's disease.
So in addition to helping with autoimmune diseases, Vitamin D has been noted for immune-system enhancing effects. Blood taken from TB patients was found to be resistant to bacterial infection after supplementation with vitamin D (7). Vitamin D deficiency and rickets was also found to an important risk factor for children developing pneumonia in Ethiopia (8).
The story in all of these diseases is a variation on the same theme: epidemiological studies show a geographical trend, then show that vitamin D is low in people with the disease. Later, more detailed studies come along to show why. Of course diabetes is different from inflammatory bowel disease and cancer. But these diseases are all largely associated with an over-active immune system, which is something that vitamin D appears to help prevent, as we will see in the next section.
Disease Prevention Vitamin D Benefits: How it works
The first clue that vitamin D was doing more than simply regulating calcium came as vitamin D receptors (VDRs) were discovered in many parts of the body beyond the intestinal tract (9). Widespread expression of vitamin D receptors and activating enzymes are also found in immune system cells (10). These findings established a role for vitamin D benefits outside the GI tract and paved the way for a series of later discoveries (11,12).
Most important among the new findings is that vitamin D functions as an immune modulator, not just suppressor or activator. At the molecular level, vitamin D upregulates expression of important immune system proteins that make immune cells more potent destroyers of invading bacteria. And on the level of immune cells, calcitriol also stimulates the conversion of monocytes into macrophages, the immune system's first line of defense against bacteria (12,14).
Recent research has shown an even more compelling link between vitamin D status and immunity. One important feature of the immune system is a group of tiny, positively charged proteins called AMPs, or antimicrobial peptides. These peptides are able to rapidly kill invading bacteria, viruses, fungi, and parasites. Vitamin D metabolites have been shown to upregulate the production of AMPs, thereby strengthening the body's natural response to invading microorganisms (15,16).
Vitamin D Benefits: What it all means
These studies all point in a general direction of a high vitamin D level being an important asset to the immune system. The relationship is complex, but mostly because we are not just talking about enhancing the immune system's capacity to ward off infections. If, however, you remain skeptical about the disease-preventing vitamin D benefits, I would suggest that you turn to the next page for a less ambiguous way that
vitamin D benefits your general health: cancer.
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4. Mathieu, C, Waer, M, Laureys, J, et al. "Prevention of autoimmune diabetes in NOD mice by 1,25 dihydroxyvitamin D3." Diabetologia. 37 (1994) 552-8.
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15. Gombart, AF, Borregaard, N, Koeffler, HP. "Human cathelidin antimicrobial peptide (CAMP) gene is a direct target of the vitamin D receptor and is strongly up-regulated in myeloid cells by 1,25-dihydroxyvitamin D3." FASEB J. 19 (2005) 1067-77.
16. Wang, TT, Nestel, FP, Bourdeau, V., et al. "Cutting edge: 1,25 dihydroxyvitamin D3 is a direct inducer of antimicrobial peptide gene expression." J Immunol. 173 (2004) 2909-12.