Major considerations and outcomes of clinical studies on vitamin d deficiency in human gut microbiota: A systematic review

Introduction: There are 2.0 billion overweight and obese people in the world, and Brazil ranks fifth in the world ranking, with an estimated 18.0 million people. The microbiota of the healthy gastrointestinal system presents around 800 species of bacteria The human microbiome has about 3 million genes in the gastrointestinal tract, corresponding to 150 times more than the human genome Vitamin D appears to interact with the immune system through its action on the regulation and differentiation of cells such as lymphocytes, macrophages, and natural killer cells. In addition, there is evidence that vitamin D interferes in vivo and in vitro production of cytokines. The vitamin D plays a significant role in modulating the immune system in the intestine, it is possible that its deficiency could impair the function of the intestinal barrier favoring the translocation of endotoxins such as lipopolysaccharides (LPS) into blood circulation. Objective: The present study aimed to investigate the main correlations and outcomes of clinical studies on vitamin D and gut microbiota. Methodology: Following the criteria of literary search with the use of the MeSH Terms that were mentioned in the item below on "Search strategies", a total of 55 clinical studies were recruited that were submitted to the eligibility analysis and, after that, 27 studies were selected. The search strategy was performed in the PubMed, Embase, Ovid and Cochrane Library, Web of Science, ScienceDirect Journals (Elsevier), Scopus (Elsevier) and OneFile (Gale) databases. Final considerations: In summary, there is a modulatory effect of vitamin D status on the intestinal immune system could influence the commensal bacterial composition and vice versa. The relatively greater abundance of gram-negative genera, such as Haemophilus and Veillonella, may be facilitated by low intake and/or concentration of vitamin D. Relatively small proportion of beneficial bacteria, such as Coprococcus and Bifidobacterium, could trigger immune response and inflammation, requiring actions as dependent on 25 (OH) D. It is concluded that vitamin D role in the maintenance of immune homeostasis seems to occur in part by interacting with the intestinal microbiota. Further studies with the appropriate design are desirable to address the hypothesis raised in the present study.