What role does B12 play in fatigue?

Vitamin B12 plays a well-established role in fatigue through its involvement in DNA synthesis, nerve myelination, and red blood cell production. Deficiency can cause megaloblastic anemia, leading to fatigue, weakness, and cognitive impairment. However, the provided context (SIBO breath tests, thyroid genetics, alcohol intolerance) contains no direct evidence or studies linking B12 to fatigue. Therefore, the evidence from this context is rated as unclear. For a robust answer, specific research on B12 levels, supplementation, and fatigue outcomes would be needed. Note: B12 deficiency can cause fatigue even without anemia; testing with holotranscobalamin or methylmalonic acid is more sensitive than serum B12 alone. Persistent fatigue warrants medical evaluation.