What role does Folsäure play in Müdigkeit?

Folic acid (vitamin B9) is crucial for DNA synthesis, cell division, and homocysteine metabolism. Deficiency can cause megaloblastic anemia, leading to fatigue and weakness. However, the role of folic acid in general fatigue without proven deficiency is controversial. Some studies suggest a link between elevated homocysteine (often due to low folate) and fatigue, but evidence is weak. Direct-to-consumer DNA tests often market MTHFR variants as a cause of fatigue, but effect sizes are small and clinically insignificant for most people. Folate deficiency should be diagnosed via blood tests (serum folate, homocysteine), not genetic testing. Supplementation without deficiency does not have proven benefit for fatigue in healthy individuals. Caveat: High-dose folic acid can mask vitamin B12 deficiency. Evidence: human-moderate (deficiency anemia), marketing/unclear (MTHFR-fatigue).