Feeling energized is less about taking random vitamins and more about correcting true deficiencies. Commonly assessed nutrients include iron stores (ferritin), vitamin B12, folate, and vitamin D. B12 supports blood formation and nervous system function; deficiency can cause fatigue and neurologic symptoms. Iron deficiency can reduce oxygen delivery and exercise tolerance. Low vitamin D may affect musculoskeletal comfort and overall well-being. The best strategy is symptom- and lab-guided supplementation alongside sleep, movement, and nutrition habits.