Myths vs facts: FUT2 and Müdigkeit

FUT2 (fucosyltransferase 2) determines secretor status, influencing gut microbiome composition and vitamin B12 absorption. A common myth is that specific FUT2 variants directly cause fatigue. In reality, GWAS and observational studies show a moderate association between non-secretor status and lower vitamin B12 levels. B12 deficiency can contribute to fatigue, but the effect size is small, and individual symptoms vary widely. Many other factors—sleep, stress, iron status, thyroid function—play a larger role. A genetic test alone cannot predict or explain fatigue. The evidence is human-moderate: the B12 link is replicated, but the direct fatigue connection remains mechanistic and insufficiently proven. Consumers should not treat such results as diagnostic or prescriptive, but interpret them in a medical context.