Vitamin B12 deficiency

What it is

Vitamin B12 deficiency is seen in two places at once: in the blood, as a macrocytic anemia of the megaloblastic kind, and in the limbs, as a polyneuropathy.

Causes and risk

The conditions that can cause vitamin B12 deficiency are a vegan diet; the use of certain drugs, for example metformin, antacids, or repeated exposure to nitrous oxide; inflammatory bowel disease or malabsorption syndromes; gastric or bariatric surgery; chronic pancreatitis; fish tapeworm infestation; and AIDS. Chronic use of a proton pump inhibitor also sits behind it. Pernicious anemia is the named cause to hold on to. It is a type of megaloblastic anemia that occurs due to vitamin B12 deficiency, often caused by autoimmune destruction of the parietal cells in the stomach, which secrete the intrinsic factor required for vitamin B12 absorption in the ileum. Grouped, the causes are malabsorption, of which pernicious anemia is one, dietary deficiency, and intrinsic factor deficiency. It goes with other autoimmune disease, which tends to cluster. Skin lesions may represent vitiligo or vitamin B12 deficiency-related changes, both of which are associated with autoimmune diseases, particularly autoimmune thyroid disease. An iron deficiency anemia beside it suggests malabsorption, which is commonly associated with autoimmune gastritis and pernicious anemia, and diarrhea can come from malabsorption of nutrients including vitamin B12 and iron.