What to watch with MTHFR and Müdigkeit?

The combination of MTHFR variants and fatigue is frequently discussed in social media and by test providers, but the scientific evidence is limited. MTHFR is an enzyme involved in converting folate into its active form (5-MTHF). Polymorphisms (e.g., C677T) can reduce enzyme activity, theoretically impairing methylation and potentially raising homocysteine levels. However, a direct causal link to fatigue is not supported by robust clinical trials. Most data come from mechanistic or population-based association studies (GWAS), which often fail to control for confounders like diet, sleep, or stress. Moreover, MTHFR variants are very common (about 30–40% of the population carry at least one copy), while fatigue is a non-specific symptom. Supplements like methylfolate are often marketed, but randomized controlled trials show no consistent benefit for fatigue without a proven deficiency. Caution: High doses of folic acid can mask a vitamin B12 deficiency. A genetic test alone is insufficient to explain fatigue – a comprehensive medical workup (including iron, vitamin D, thyroid) is more appropriate. Evidence grade: unclear / mechanistic.