For centuries, the devastating effects of the disease beriberi were known in Asian countries where white rice was the main (or staple) food. White rice is milled and therefore no longer contains the nutrient-rich germ. In the late 1800s, beriberi became even more common and one of the leading causes of death. This occurred because rice milling technology introduced at that time completely removed the bran and the germ, resulting in highly polished rice but also stripping the rice grains of their thiamin content. However, scientists did not link the disease beriberi with a nutrient deficiency until early in the 1900s, when it was discovered that a vital factor in the rice germ cures beriberi. That factor is the B-vitamin thiamin, also known as B-1.
Thiamin consists of a central carbon attached to a6-member nitrogen-containing ring and a 5-member sulfur-containing ring. Its name comes from thio, meaning “sulfur”, and amine, referring to the nitrogen groups in the molecule. Two phosphate groups are added to form this vitamin’s coenzyme, thiamin pyrophosphate (TPP).
THIAMIN IN FOODS
Thiamin is found in a wide variety of foods, although generally in small amounts. Foods rich in thiamin are pork products, sunflower seeds, and legumes. Whole and enriched grains and cereals, green peas, asparagus, organ meats, peanuts, and mushrooms are also good sources.
FUNCTIONS OF THIAMIN
The coenzyme thiamin pyrophosphate (TPP) is required for the metabolism of carbohydrates and branched-chain amino acids. TPP is necessary for two different types of reactions. First, it works with the specific enzymes to remove carbon dioxide (known as decarboxylation) from certain compounds. The conversion of pyruvate to acetyl-CoA, a critical reaction in the aerobic metabolism of glucose, is an example of the decarboxylation action of TPP.
ABSORPTION, TRANSPORT, STORAGE, AND EXCRETION OF THIAMIN
Thiamin is absorbed mainly in the small intestine by a sodium-dependent active absorption process. It is transported mainly by red blood cells in its coenzyme form (thiamin pyrophosphate). Little thiamin is stored; only a small reserve is found in muscles and the liver. Ant excess intake is rapidly filtered out by the kidneys and excreted in the urine.
THIAMIN NEEDS AND UPPER LEVEL
The RDAs for thiamin are 1.2 mg per day for adult men and 1.1 mg per day for women. The Daily Value on food and supplement labels is 1.5 mg. The average daily intake for thiamin in the U.S. for young men is close ti 2 mg per day. For young women, it is approximately 1.2 mg daily. There appears to be no adverse effect with excess intake if thiamin from food or supplements because it is readily excreted in the urine. Thus, no Upper Level is established for this nutrient.
THIAMIN DEFICIENCY
BeriBeri
The thiamin-deficiency disease beriberi has been associated with diets consisting mainly of white rice. For example, in the 1800s, 25 ro 40% of those in the Japan navy experienced beriberi because ship rations included white rice and little else. When meat and legumes were added to the navy ratios, beriberi was eliminated. Although much less common today, beriberi still occurs among poor people in developing countries where rice is the staple food.
In Sinhalese, the language if Sri Lanka, the word beriberi means “I can’t, I can’t”. Those with beriberi are very weak because a deficiency of thiamin impairs the nervous, muscle, gastointestinal, and cardiovascular system. The symptoms of beriberi include peripheral neuropathy and weakness, muscle pain and tenderness, enlargement of the heart, difficulty breathing, edema, anorexia, weight loss, poor memory, and confusion.
The nervous system is especially affected because of its reliance on glucose for energy. In thiamin deficiency, glucose metabolism is severely disrupted because pyruvate cannot be coverted to acetyl-CoA, the entry compound into the citric acid cycle.
Beriberi is often described as either dry or wet beriberi. In dry beriberi, the main symptoms are related to the nervous and muscular systems. In wet beriberi, in addition to the neurological symptoms, the cardiovascular system is affected. The heart is enlarged, breathing may be difficult, and congestive heart failure may occur. Like most water-soluble vitamins, only small amounts of thiamin are stored in the body. Thus, some signs of beriberi can develop after only 14 days on a thiamin-free diet.
Wernicke-Korsakoff Syndrome
Wernicke-Korsakoff Syndrome (also known as cerebral beriberi) is found mainly among heavy users of alcohol. These individuals have a 3-pronged problem related to thiamin: alcohol decreases thiamin absorption, alcohol increases thiamin excretion in the urine, and alcoholics may consume a poor-quality diet without enough thiamin. Because thiamin is not readily stored in the body, the syndrome can occur rapidly. The symptoms include changes in vision (double vision, crossed eyes, rapid eye movements), ataxia, and impaired mental functions. The symptoms, especially those of the eye, improve with high doses of thiamin.
