Can MTHFR help with fatigue?

Whether MTHFR can help with fatigue is not clearly supported by evidence. MTHFR (methylenetetrahydrofolate reductase) is an enzyme central to folate metabolism and methylation. Certain variants (e.g., C677T) can reduce enzyme activity and raise homocysteine levels. Some studies suggest a link between elevated homocysteine and fatigue, but the evidence is weak and inconsistent. Most research is mechanistic or based on small samples; large randomized trials are lacking. Moreover, direct-to-consumer genetic tests often overstate MTHFR's role. A positive result does not mean fatigue is caused by MTHFR. Other factors—sleep, stress, diet, thyroid function—are far more influential. Supplementation with active folate (5-MTHF) may be reasonable if a deficiency is confirmed, but not as a blanket remedy for fatigue. Conclusion: MTHFR is a plausible but poorly substantiated factor. Evidence is mechanistic and mixed.