What to watch with Folsäure and fatigue?

The question about folic acid and fatigue is clinically relevant, but the provided context contains no direct information on this topic. Folic acid deficiency can indeed cause fatigue and weakness, as folate is essential for DNA synthesis and red blood cell production. Deficiency leads to megaloblastic anemia, whose hallmark symptom is fatigue. However, caution is warranted: high doses of folic acid (≥1 mg/day) can mask vitamin B12 deficiency, which also causes fatigue but can lead to irreversible neurological damage. Additionally, genetic variants (e.g., MTHFR C677T) may impair conversion of folic acid to active folate. Consumer DNA tests often provide weak evidence (effect sizes <5%). The clinical recommendation remains: for fatigue, first get a medical workup (CBC, B12, folate, ferritin, TSH) before supplementing folic acid. Evidence: human-moderate (for deficiency-fatigue), mechanistic (for masking). No relevant sources from the given context.