- B-12 or folic acid deficiency o These are usually from leafy vegetables, meat sources. main cause is autoimmune condition on elderly, smaller stomach and the IF product decreases The parietal cells in the stomach secretes a glycoprotein called the intrinsic factor, B-12 naturally binds to the intrinsic factor. Some individuals their immune system somehow produces antibodies that will bind to the intrinsic factor therefore inhibiting B12. Hemoglobin not functioning; less oxygen; stuck in capillaries Macrocytic: If the MCV is greater than 90 fL