Is Homocystein useful for fatigue?

Homocysteine is sometimes measured in fatigue workups because elevated levels can indicate deficiencies in vitamin B12, B6, or folate, which are involved in energy metabolism. However, the evidence for a direct causal link between homocysteine and fatigue is weak. Studies show homocysteine is primarily a cardiovascular risk marker, not a specific fatigue biomarker. Supplementing B vitamins lowers homocysteine but does not consistently improve fatigue symptoms. For chronic fatigue, other causes like sleep disorders, iron deficiency, or thyroid dysfunction should be investigated first. Homocysteine testing may be useful if a B-vitamin deficiency is suspected, but it is not recommended as a routine screening for fatigue. The evidence is moderate and does not support widespread use. Caveat: DTC labs often overstate the relevance of homocysteine for fatigue.