What to watch with B12 and fatigue?

The provided context does not contain specific information about vitamin B12 and fatigue. In general, B12 deficiency is a known cause of fatigue, especially in vegans, older adults, or those with malabsorption. A blood test (e.g., holotranscobalamin) is more reliable than serum B12 alone. Without lab results or genetic data from the context, no personalized advice can be given. Persistent fatigue should be evaluated by a physician to rule out B12 deficiency and other causes (iron, thyroid, sleep disorders).