Thiamine (Vitamin B1)
Thiamine operates in the metabolic systems of the body principally as thiamine pyrophosphate; this compound functions as a cocarboxylase, operating mainly in con-junction with a protein decarboxylase for decarboxyla-tion of pyruvic acid and other a-keto acids.
Thiamine deficiency (beriberi) causes decreased uti-lization of pyruvic acid and some amino acids by the tissues, but increased utilization of fats. Thus, thiamine is specifically needed for the final metabolism of carbo-hydrates and many amino acids. The decreased utiliza-tion of these nutrients is responsible for many debilities associated with thiamine deficiency.
Thiamine Deficiency Causes Lesions of the Central and Peripheral Nervous Systems. The central nervous system normallydepends almost entirely on the metabolism of carbohy-drates for its energy. In thiamine deficiency, the utiliza-tion of glucose by nervous tissue may be decreased 50 to 60 per cent and is replaced by the utilization of ketone bodies derived from fat metabolism. The neu-ronal cells of the central nervous system frequently show chromatolysis and swelling during thiamine defi-ciency, changes that are characteristic of neuronal cells with poor nutrition. These changes can disrupt communication in many portions of the central nervous system.
Thiamine deficiency can cause degeneration of myelinsheaths of nerve fibers in both the peripheral nerves andthe central nervous system. Lesions in the peripheral nerves frequently cause them to become extremely irri-table, resulting in “polyneuritis,” characterized by pain radiating along the course of one or many peripheral nerves. Also, fiber tracts in the cord can degenerate to such an extent that paralysis occasionally results; even in the absence of paralysis, the muscles atrophy, result-ing in severe weakness.
Thiamine Deficiency Weakens the Heart and Causes Peripheral Vasodilation. A person with severe thiamine deficiencyeventually develops cardiac failure because of weak-ened cardiac muscle. Further, the venous return of blood to the heart may be increased to as much as two times normal. This occurs because thiamine deficiency causes peripheral vasodilation throughout the circula-tory system, presumably as a result of decreased release of metabolic energy in the tissues, leading to local vas-cular dilation. The cardiac effects of thiamine deficiency are due partly to high blood flow into the heart and partly to primary weakness of the cardiac muscle.
Peripheral edema and ascites also occur to a majorextent in some people with thiamine deficiency, mainly because of cardiac failure.
Thiamine Deficiency Causes Gastrointestinal Tract Disturbances.
Among the gastrointestinal symptoms of thiamine defi-ciency are indigestion, severe constipation, anorexia, gastric atony, and hypochlorhydria.All these effects pre-sumably result from failure of the smooth muscle and glands of the gastrointestinal tract to derive sufficient energy from carbohydrate metabolism.
The overall picture of thiamine deficiency, including polyneuritis, cardiovascular symptoms, and gastro-intestinal disorders, is frequently referred to as beriberi—especially when the cardiovascular symptoms predominate.