Vitamin B-1; Thiamin

Thiamin

Vitamin B-1

In the late 1800s, beriberi became even more common and one of the leading causes of death. This occurred because the rice-milling technology introduced at that time completely removed the bran and the germ, resulting in highly polished white 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 rice germ cures beriberi. That factor is the B-vitamin thiamin, it also known as vitamin B-1.

Structure of Thiamin:

 

 Thiamin consists of a central carbon attached to a 6-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) (also called thiamin diphosphate).

 The chemical bond between each ring and the central carbon in thiamin is easily broken by prolonged exposure to heat, as can occur in cooking. When this happens, the vitamin can no longer function in the body. Thiamin also is susceptible to destruction in alkaline conditions.  Adding baking soda to the cooking water water of green vegetables helps keeps them bright green but this practice destroys thiamin and it is not recommended.

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 (e.g., liver), peanuts, and mushrooms also are good sources. In the U.S., major contributors of thiamin are bread and rolls, ready-to-eat cereals, pasta, ham, milk, bakery products, potatoes, rice, orange juice, tomatoes, and beef. Eating a variety of foods in accord with MyPlate is a reliable way to obtain sufficient thiamin.

A few foods contain compounds, called thiamin antagonists, that lower the bioavailability of thiamin. Some species of fresh fish and shellfish contain thiaminase enzymes that destroy thiamin. Cooking inactivates these enzymes. Other foods, including coffee, tea, blueberries, red cabbage, brussels sprout, and beets, contain compounds that oxidize thiamin and make it inactive. However, eating these foods has not been linked to thiamin deficiency.

Thiamin Needs and Upper level:

The RDAs for thiamin are 1.2 mg/day for adult men and 1.1 mg/day for women. The Daily Value on food and supplement labels is 1.5 mg. The average daily intake for thiamin factor food in the U.S. for men is 1.95 mg/day. For women, it is approximately 1.4 mg/day. There appear to be  adverse effects with excess intake of thiamin from food or supplements because it is readily excreted in the urine. Thus, no Upper Level is established for this nutrient.

Absorption, Transport, Storage & 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 is stored; only a small reserve (25-30 mg) is found in the muscles, brain, liver, and kidneys. Any excess intake is rapidly filtered out by the kidneys and excreted in the urine.

Functions of Thiamin:

The coenzyme thiamin pyrophosphate (TPP) is required for the metabolism of carbohydrates and branched-chain amino acids. TPP is necessary for 2 different types of reactions. First, it works with 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 respiration of glucose, is an example of the decarboxylation action of TPP.

Thiamin is required for normal functions of the nervous system. The nervous system relies on glucose for energy. In thiamin deficiency, glucose metabolism is severely disrupted because pyruvate cannot be converted to acetyl-CoA, the compound that enters into the citric acid cycle. However, researchers believe that thiamin may have additional critical functions in the nervous system.

Thiamin Deficiency:

The thiamin deficiency disease beriberi is associated with diets consisting mainly of white rice. For example, in the 1800s, 25 to 40% of those in the Japanese navy experienced beriberi because ship rations included white rice and little else. When meat and legumes were added to the navy rations, beriberi was eliminated. Although much less common today, beriberi is still a problem in parts of Asia, particularly among refugees and impoverished elderly people and infants. Individuals who abuse alcohol and those with heart failure, gastrointestinal diseases, or eating disorders, as well as the elderly, also are at risk of thiamin deficiency.

Beriberi:

Those with beriberi are weak because a deficiency of thiamin impairs the nervous, muscle, gastrointestinal, and cardiovascular systems. The symptoms of beriberi include peripheral neuropathy, and weakness, muscle pain and tenderness, enlargement of the heart, edema, difficulty in breathing, anorexia, weight loss, poor memory and confusion.

Beriberi is often described as dry, wet or infantile 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. Infants develop beriberi when breast milk contains insufficient thiamin. Infantile beriberi causes heart problems, convulsions, even death if not treated promptly. Like most water-soluble vitamins, only small amount of thiamin are stored in the body. Thus, some signs of thiamin deficiency can develop after only 14 days on a thiamin-free diet.

Wernickle-Korsakoff Syndrome:

Wernickle-Korsakoff syndrome 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 (Inability to coordinate muscle activity during voluntary movement; incoordination) , confusion and apathy. The symptoms, especially those of the eye, improve with high doses of thiamin.