Is BDNF useful for fatigue?

BDNF (Brain-Derived Neurotrophic Factor) supports neuronal survival and plasticity. Some research links low BDNF levels to fatigue, particularly in chronic fatigue syndrome or after strenuous exercise. However, the evidence is largely mechanistic and observational; BDNF is not a validated standalone biomarker for general fatigue. Blood levels fluctuate with circadian rhythm, physical activity, and stress, making single measurements unreliable. Consumer tests can indicate trends but cannot diagnose fatigue causes. Persistent tiredness warrants a medical workup for thyroid, iron, sleep, or other issues. BDNF may be useful in research or multi-marker panels, but alone it lacks sufficient specificity. Evidence: mechanistic/moderate; not ready for clinical or consumer decision-making.