Vitamin D Test: can a microbiome test help?

A microbiome test cannot directly measure vitamin D status. The clinical gold standard is a blood test for 25-hydroxyvitamin D. Some research suggests the gut microbiome may influence vitamin D absorption and metabolism (e.g., via bile acid modification), but this is not a validated diagnostic marker. Microbiome tests are currently not appropriate to confirm or rule out vitamin D deficiency. The evidence is mechanistic and insufficient for clinical decisions. A vitamin D blood test remains the direct and reliable method.