Is Folsäure useful for fatigue?

Folic acid (vitamin B9) is crucial for red blood cell formation and energy metabolism. In cases of confirmed folate deficiency—which can cause megaloblastic anemia and fatigue—supplementation is clearly beneficial. However, evidence for folic acid in general, non-deficient fatigue is weak. Most trials show no benefit in individuals with normal folate levels. Additionally, high folic acid intake can mask vitamin B12 deficiency, a concern especially for older adults and vegans. Marketing of 'anti-fatigue' supplements containing folic acid often overstates the science. A blood test (holotranscobalamin, homocysteine, serum folate) is advisable before supplementing. Without deficiency, folic acid is not evidence-based for fatigue.