Vitamin B12 deficiency occurs when the body lacks sufficient B12, crucial for nerve function, red blood cell formation, and DNA synthesis, leading to symptoms like fatigue, weakness, numbness, cognitive issues (memory loss, confusion), mood changes (depression), pale skin, and a sore tongue, often due to poor absorption, strict vegan diets, or lack of intrinsic factor. It can cause megaloblastic anemia and neurological damage, but is treatable with supplements or injections, though addressing the underlying cause is key.
