Fatigue is commonly linked to anemia (often iron deficiency) and low vitamin B12/folate; vitamin D insufficiency, inadequate protein intake, and low overall calorie intake can also contribute. Iron depletion can reduce performance even before hemoglobin drops (low ferritin). B12 deficiency may add neurologic symptoms such as tingling, balance issues, or cognitive changes. Thyroid disorders—especially hypothyroidism—are another frequent cause. A targeted workup (CBC, ferritin/iron, B12, folate, vitamin D, TSH) guided by symptoms is safer than high-dose self-supplementation, which can mask underlying disease or cause adverse effects.