Evidence check: B12 in the context of Darmgesundheit

The evidence linking vitamin B12 to gut health is well-established, but the strength varies by context. A healthy gut is critical for B12 absorption: intrinsic factor in the stomach and uptake in the terminal ileum require intact mucosa. In conditions like Crohn's disease, ulcerative colitis, celiac disease, or atrophic gastritis, B12 absorption is often impaired – here the evidence is strong (human-strong). For general 'gut health' in healthy individuals, the link is more moderate: the gut microbiome can synthesize B12, but the amount is usually negligible for human needs. A DNA test for MTHFR variants (as mentioned in the context) affects folate metabolism, not B12 directly, though B12 and folate are often co-supplemented. Caveat: A DNA result alone, without blood biomarkers (holotranscobalamin, homocysteine), has limited clinical utility. If malabsorption is suspected, a physician should measure B12 levels. Safety note: B12 deficiency can cause irreversible neurological damage – supplementation under medical guidance is advisable for at-risk groups.