Walsh & Hoyt: Vitamin B12 Deficiency

Although the role of vitamin B12 in the maintenance and function of the nervous system has yet to be explained, depletion of the nutrient almost invariably leads to neurologic dysfunction. The body's nutritional requirements must be met entirely by food (particularly meat and dairy products). The abundant stores, particularly in the liver, are redistributed so gradually that it takes years for poor intake to cause disease. However, a poor diet is rarely the cause of vitamin B12 deficiency and when it is, it is found only in strict vegans. Impaired absorption because of diphyllobothriasis, intestinal disease, or gastrointestinal surgery accounts for only a few cases.