Myths vs facts: VDR and gut health

Claims that VDR (Vitamin D Receptor) gene variants strongly and directly determine gut health are often overstated. Mechanistic evidence shows VDR is expressed in intestinal epithelial and immune cells, and it modulates barrier function, inflammation, and the microbiome. VDR knockout mice develop gut dysbiosis and increased susceptibility to colitis. However, in humans, the effects of common VDR polymorphisms (e.g., FokI, TaqI) are small, inconsistent, and heavily confounded by vitamin D status, diet, and microbiota composition. Most human studies are observational or small intervention trials; large randomized controlled trials are lacking. Direct-to-consumer genetic tests that claim to predict gut health from VDR variants are based on weak evidence and often overpromise. The current science supports a role for vitamin D in gut health, but not a strong, actionable genetic effect. Evidence: mechanistic, human-moderate. Sources: none from provided context.