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Water Soluble Vitamins

Thiamin

Terms for Water-Soluble Vitamins

Riboflavin

Function

Thiamin, or vitamin B1, plays a major role in carbohydrate metabolism. Thiamin acts as a coenzyme along with phosphorus in important cellular reactions such as decarboxylation and transketolation. Thiamin pyrophosphate (TPP), a coenzyme, allows pyruvate to enter the citric acid cycle (Krebs' cycle) to produce energy for cellular functions. TPP acts in fat synthesis by transketolation, providing glyceraldehyde for the conversion of glucose to fat.

Thiamin is thought to be involved in neurotransmission and nerve conduction. Thiamin triphosphate may play a role in the control of sodium conductance at axon membranes.

Absorption and excretion

Thiamin is absorbed quite easily in the jejunum and ileum. Thiamin is transported to the liver in the blood. High amounts of thiamin are stored in the skeletal muscles, heart, liver, kidneys, and brain. Approximately one-half of the thiamin is stored in the muscles. The half-life of thiamin in the body is 9 to 18 days. Thiamin is mainly excreted in the urine.

Clinical conditions

Thiamin deficiency, called beriberi, effects the nervous system due to its dependence on glucose for energy. Insufficient thiamin can result in diminished alertness and reflexes, apathy, and fatigue. Thiamin deficiency affects lipogenesis and results in degeneration of the lipid myelin sheaths covering the nerve fibers. Clinical symptoms include pain and prickly sensations, and in a severe deficiency paralysis can result. Gastrointestinal symptoms include indigestion, constipation, gastric atony, deficient hydrochloric acid secretion, and anorexia. Thiamin deficiency also can weaken the heart muscle, leading to cardiac failure and edema in the extremities. A disease called Wernicke-Korsakoff syndrome results in ocular motor signs, ataxia, and deranged mental function. Most patients with Wernicke-Korsakoff syndrome are alcoholics, but few alcoholics actually develop the disease.

Recommended intake

The DRI for thiamin is: 0.2-0.3 mg for infants, 0.5-0.6 mg for children, 0.9-1.2 mg for adolescents, 1.2 mg for men, 1.1 mg for women, and 1.4 mg for pregnant and lactating women. Requirements are somewhat dependent on energy intake due to thiamin's primary role in energy metabolism.

Food Sources

Thiamin is found in small quantities in many plant and animal foods. Sources include lean pork, beef, liver, yeast, whole grains, enriched grains, and legumes.

Figure %: Thiamin Content of Selected Foods

Supplementation

Thiamin therapy is used in the treatment of alcoholics. Malnutrition often develops from alcohol and a poor diet, leading to neurological disorders. Infections increase cellular energy requirements and therefore thiamin requirements. Thiamin administration to beriberi patients ranges from 50-100 mg given intravenously or intramuscularly for one or two weeks. The dose can then be dropped to 10 mg until the patient recovers.

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