According to an observational study on 567 older men, having higher concentrations of a vitamin D metabolite, 1,25(OH) 2D, is associated with a greater “activation ratio” of vitamin D, as well as an association with more butyrate-producing bacteria that are linked to better gut health. While the association with gut health was present in the vitamin D metabolite, it was not present in serum concentrations of “unactivated” vitamin D itself.
 
The mean age of the men was 84 years, and they were overall very physically active. Most reported taking some form of vitamin D supplementation, with almost 7% of the men reporting that they took antibiotics within the 30 days preceding the pandemic.
 
“It is the active form of vitamin D, 1,25(OH)2D, that interacts specifically with the vitamin D receptor and transacts gene expression,” the authors of the study said. “Here we show that in 567 community-dwelling older men, higher levels of the biologically active form (1,25(OH)2D) and vitamin D activation and catabolism ratios, but not 25(OH)D, are associated with greater a-diversity.”
 
A-diversity represents a measurement of diversity in the bacterial flora present in the gut.
 
“Those men with the highest compared to lowest 1,25(OH)2D and activation ratios are more likely to possess butyrate-producing bacteria that are associated with favorable gut microbial health. These results support the underlying hypothesis that the human gut microbiome and vitamin D metabolism are integrally related,” the authors continued.
 
Compared to race, site, BMI, the use of various drugs, age, physical activity, and total starch intake, serum levels of activated vitamin D were most heavily linked to gut microbiome diversity, suggesting a significant association.
 
“Our results suggest that it is the regulation of vitamin D metabolism (VDM), reflected by the active hormone and metabolic ratios rather than body stores that may have the most health implications,” the authors of the study concluded. Further, they stated that the study could not determine the causality between enhanced vitamin D signaling and gut microbiome diversity, in terms of which causes the other. However, previous animal studies have stipulated that gut microbiota effect the vitamin D metabolism of a host.
 
“The consistency and robustness of results in finding active vitamin D metabolites associated with more favorable gut microbial diversity, including specific microbiota that are known butyrate producers, provide potential targets for intervention, whether through dietary modification and/or vitamin D supplementation in clinically appropriate populations,” the researchers added.