Module 3.6: Vitamin D Supplementation

Vitamin D has some very important eubiotic functions in the GM that make it an excellent addition to a GM optimizing protocol. The mechanisms Vitamin D uses to regulate the GM are not fully understood at this time, however, Vitamin D is known to induce the expression of antimicrobial peptides in the GM (45,46,47). These antimicrobial peptides help to inhibit and prevent the growth of pathogenic and inflammatory bacteria in the GM (45,46,47). This pushes the GM towards eubiosis by giving probiotic microorganisms the opportunity to thrive (45,46,47). As a result of this and other mechanisms, Vitamin D supplementation helps to prevent inflammation and strengthens the tight junctions between the intestinal epithelial cells (45,48).

In a 4 week intervention trial for Crohn’s Disease patients, Vitamin D supplementation was concluded to have a strong effect on the GM composition of CD patients due to there being an increase in the number of microorganisms that are thought to be beneficial during the trial (49,50). The CD activity index and fecal calprotectin levels, a marker of intestinal inflammation, both showed an overall decrease, though the decreases were not statistically significant (50). It was found in another study that vitamin D deficient patients with active Ulcerative Colitis did see a statistically significant decrease in fecal calprotectin levels after supplementing with a total of 40,000 IUs of Vitamin D each week for 8 weeks (51). The UC patients in this study also saw a shift in the composition of their GMs following Vitamin D supplementation, though the significance wasn’t entirely understood due to uncertainty about whether or not the bacteria that increased were probiotic or pathogenic in nature (51). It would seem that the bacteria would be probiotic in nature since the UC patients saw a decreased level of intestinal inflammation, and because Vitamin D is known to regulate the expression of antimicrobial peptides that help to inhibit and prevent the growth of pathogenic and inflammatory bacteria (45,46,47,51).

A large systematic review and meta-analysis conducted in 2020 concluded that Vitamin D supplementation in deficient IBD patients improved Vitamin D levels, reduced inflammatory biomarkers, such as C-reactive protein, and reduced other disease activity scores (52).

The key points are that Vitamin D supplementation provides a small, but significant, eubiotic effect, it decreases inflammation, strengthens TJ proteins, and decreases disease activity in IBD patients (45,46,47,48,52,53). The tolerable upper intake level of vitamin D, as determined by the Institute of Medicine, is 4,000 IUs per day for ages 9 and older (54). However, the proper dosage of Vitamin D for IBD patients has not been established yet, so I would recommend asking your doctor what amount of Vitamin D would be appropriate for you to supplement with on a daily basis (52).

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