The cause of beriberi was determined to be deficiency of thiamine (vitamin B1), a water-soluble and heat-labile vitamin required for carbohydrate metabolism. Thiamine is essential for most vertebrates and some microorganisms. Beriberi has 2 main forms in humans, depending on the system of maximum involvement. Wet (edematous) beriberi is a cardiovascular dysfunction that is usually chronic but may have an acute presentation. Dry beriberi is a multifocal peripheral and/or central neurologic dysfunction, which includes Wernicke encephalopathy and Korsakoff syndrome. Often times, patients present with involvement of both systems.
Thiamine mainly functions as thiamine pyrophosphate (TPP), which serves as a prosthetic group or cofactor for 3 enzymes essential to carbohydrate metabolism. Pyruvate dehydrogenase is the last step in the catabolism of glucose for energy, glycolysis, and yields acetyl coA, which is required to synthesize acetylcholine, an important neurotransmitter.
Impaired energy production, increased manufacturing of free radicals, decreases in neurotransmitters, and possible N -methyl-D-aspartate (NMDA) receptor–mediated toxicity have been hypothesized to yield the neuronal injury seen in dry beriberi.
Sources of Thiamine
Thiamine is not widely distributed in high concentrations; consequently, many foods are now routinely fortified with it. Rich natural sources include whole grains, lean pork, peas, spinach, and legumes. Very little thiamine is present in fats, oils, and refined sugars. It is destroyed by heat, pasteurization, and ionizing radiation. Freezing does not affect the bioavailability of thiamine;