Introduction to Thiamine (Vitamin B1)

Thiamine (vitamin B1) provides the functional group for the coenzyme thiamine pyrophosphate, which is involved in decarboxylation of pyruvate and -ketoglutarate and, thus, is important in the release of energy from carbohydrates. It also participates in the hexose monophosphate shunt that generates nicotinamide adenine dinucleotide phosphate and pentose.

Thiamine also is required for the synthesis of acetylcholine, and deficiency results in impaired nerve conduction.

Good sources of thiamine include meat, legumes, and cereals. Unless enriched, refined cereals and flours have a much lower content of thiamine than whole grains. The vitamin is easily destroyed by heat, particularly in alkaline media, and significant amounts are lost in discarded cooking water. The breast milk of a well-nourished mother provides adequate thiamine; breast-fed infants of thiamine-deficient mothers, however, are at risk for deficiency. Most infants and older children obtain an adequate intake of thiamine from food and do not require supplements.

Thiamine is absorbed efficiently in the gastrointestinal tract, but may be decreased in persons with gastrointestinal or liver disease.

Deficiency (beriberi) has been reported in adolescents after gastric bypass surgery. Intakes in excess of tissue needs are excreted in the urine. Fever and/or stress may increase the requirement for thiamine and unmask marginal thiamine sufficiency, but these factors are unlikely to cause deficiency.

Thiamine dependence has been described in a child with megaloblastic anemia and in an infant with otherwise typical maple syrup urine disease. In addition, the urine of children with Leigh encephalomyelopathy as well as that of their parents inhibits the formation of thiamine pyrophosphate, and large doses of thiamine improve some of the abnormalities associated with the disease.

Clinical Features of Thiamine Deficiency:
Early manifestations of thiamine deficiency include fatigue, apathy, irritability, depression, drowsiness, poor mental concentration, anorexia, nausea, and abdominal discomfort.

As the condition progresses, other manifestations include peripheral neuritis, with tingling, burning, and paresthesias of the toes and feet; decreased deep tendon reflexes; loss of vibration sense; tenderness and cramping of the leg muscles; congestive heart failure; and psychic disturbances. Patients may have ptosis of the eyelids and atrophy of the optic nerve. Hoarseness or aphonia caused by paralysis of the laryngeal nerve is a characteristic sign. Muscle atrophy and tenderness of the nerve trunks are followed by ataxia, loss of coordination, and loss of deep sensation. Later signs include increased intracranial pressure, meningismus, and coma.

An epidemic of life-threatening thiamine deficiency was seen in infants fed a defective soy-based formula that had undetectable thiamine levels. Manifestations included emesis, lethargy, restlessness, ophthalmoplegia, abdominal distention, developmental delay, failure to thrive, lactic acidosis, nystagmus, diarrhea, apnea, and seizures. Intercurrent illnesses that resembled Wernicke encephalopathy often precipitated the symptoms.

A severe deficiency of thiamine leads to the deficiency disease beriberi.Two forms exist, wet beriberi and dry beriberi. The child with wet beriberi is undernourished, pale, and edematous; has dyspnea, vomiting, and tachycardia; and has waxy skin. The urine often contains albumin and casts. The child with dry beriberi appears plump, but is pale, flabby, and listless, with dyspnea, tachycardia, and hepatomegaly.

Death from thiamine deficiency usually is secondary to cardiac involvement. The initial signs are slight cyanosis and dyspnea, but tachycardia, enlargement of the liver, loss of consciousness, and convulsions may develop rapidly. The heart, especially the right side, is enlarged. The electrocardiogram shows an increased Q-T interval, inverted T waves, and low voltage. These changes as well as the cardiomegaly rapidly revert to normal with treatment, but without prompt treatment, cardiac failure can develop rapidly and result in death. In fatal cases of beriberi, lesions are located principally in the heart, peripheral nerves, subcutaneous tissue, and serous cavities. The heart is dilated, and fatty degeneration of the myocardium is common. Generalized edema or edema of the legs, serous effusions, and venous engorgement are often present. Degeneration of myelin and axon cylinders of the peripheral nerves, with wallerian degeneration beginning in the distal locations, also is common, particularly in the lower extremities. Lesions in the brain include vascular dilation and hemorrhage.

Toxicity of Thiamine:
There are no reports of adverse effects from consumption of excess thiamine by ingestion of food or supplements. A few isolated cases of pruritus and anaphylaxis have been reported in patients after parenteral administration of the vitamin.