The gut is the seat of the majority of the immune system and many studies have shown the relationship between microbes and overall health. The gut is compromised of a multitude of organisms which need a happy home to flourish. There are a number of nutrients that support that happy home including vitamin D and B vitamins, this linked article explores these relationships. This is a snippet: RESULTS: Three months of vitamin D plus B100 resulted in improved sleep, reduced pain and unexpected resolution of bowel symptoms. These results suggest that the combination of vitamin D plus B100 creates an intestinal environment that favors the return of the four specific species, Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria that make up the normal human microbiome. https://www.ncbi.nlm.nih.gov/pubmed/27515213