B - 12 also helps prevent a type of anemia called megaloblastic anemia that makes people tired and weak. (enduropacks.com)
Individuals with autoimmune diseases such as megaloblastic anemia do not produce enough of a substance called intrinsic factor, which is required for the body to absorb vitamin B12 in the digestive tract, and in turn, they develop vitamin B12 deficiency. (healthyeating.sfgate.com)
Vitamin B12 deficiency is characterized by megaloblastic anemia, fatigue, weakness, constipation, loss of appetite, and weight loss [1,3,27]. (ods.od.nih.gov)