What to watch with B12 and gut health?

When considering B12 and gut health, the key is understanding absorption. B12 requires intrinsic factor (stomach) and a healthy ileum. Gut microbiome does not produce B12; it's obtained from animal foods or supplements. Consumer DNA tests may include variants in MTHFR, FUT2, or TCN1, but these have small, inconsistent effects on B12 status. No robust evidence supports using these SNPs to guide supplementation or gut health decisions. A clinical blood test (holotranscobalamin, MMA) is far more reliable. Be cautious: high-dose B12 can mask folate deficiency, and gut health is multifactorial. Evidence: marketing/unclear.