Vitamin B1-This is one of the 9 water-soluble vitamins and of course, one of the B vitamins. Vitamin B1 is also known as thiamine. Thiamin functions as a cofactor in the oxidative decarboxylation of alpha-keto acids. For example, alpha-ketoglutarate, is converted to succinyl CoA by the enzyme alpha-ketoglutarate dehydrogenase. This enzyme complex requires vitamin B1 as a cofactor, as well as lipoic acid, NAD+, FAD, and CoA.
Before vitamin B1 (thiamine) can be used as a cofactor for this enzyme, it must be converted to the active form, which we call thiamine pyrophosphate (TPP). Thiamine is converted into TPP by addition of a pyrophosphate group from ATP to thiamine. ATP is a molecule that supplies phosphates and energy for many reactions in the body. ATP is also used in reactions such as those while contracting muscle tissue, and many others. The active form of thiamine is also used as a cofactor for the enzyme alpha-transketolase. Alpha-transketolase forms and degrades alpha-ketols in the pentose phosphate pathway, which is a series of reactions supplying intermediates for nucleotide synthesis and glycolysis. These reactions supply parts for genetic material in cells, and help to utilise carbohydrates. Thiamine is needed for these reactions.
Sources of thiamine
Thiamine can be found in pork, organ meats, legumes, nuts, and whole grain or enriched cereals and breads. The outer layer of seeds are rich in thiamine. This is the premise for whole wheat bread being more nutritious for the consumer, versus white bread, which is prepared from milled grain and is low in thiamine.
RDA of thiamine
The amount of thiamine required in the diet is proportional to the amount of caloric intake. 0.5 mg (half of a milligram) is required for each 1000 kcal in the diet. For the average male who consumes 3000 kcal/day, this equates to 1.5 mg of thiamine per day. The typical UK and US diets provide less than 0.8 mg.day, thus we seem to be shortchanging ourselves a bit when it comes to thiamine. Small supplemental doses of thiamine can be taken to provide the RDA. And of course, some personal diets, or from various cultural diets can supply the necessary amounts.
Deficiency of thiamine
Without thiamine the energy metabolism of most tissues cannot proceed correctly. This is because the dehydrogenase reactions which require activated thiamine (TPP) as a cofactor produce a reduced amount of ATP.
Wernicke-Korsakoff syndrome
In the US and UK, thiamine deficiency is observed primarily in chronic alcoholism. This is most likely due to dietary insufficiency (not eating properly) and impaired intestinal absorption of thiamine. A percentage of those suffering from chronic alcoholism develop Wernicke-Korsakoff syndrome, a thiamine deficiency state characterized by amnesia (memory loss), apathy, and a rhythmical back and forth motion of the eyes. If the individual is not quickly treated with thiamine, coma, irreversible brain damage and death can result.
Beri-Beri
Beri-Beri, which comes from Singhalese, meaning "I cannot", signifies that the person is too ill to do virtually anything. Beri-Beri is a severe thiamine deficiency observed in areas where polished rice composes the major portion of the diet. Infantile Beri-Beri is characterized by tachycardia (rapid heart rate), vomiting, convulsions, and death, if not treated. Infantile Beri-Beri has a quick onset in nursing infants where the mothers are deficient in thiamine. The mother will use most of the already low source of thiamine, and the infant will get barely enough to survive. Adult Beri-Beri is characterized by dry skin, irritability, impaired cognition and progressive paralysis.
Thiamine toxicity
Thiamine toxicity is rarely seen but can occur with large chronic supplemental doses of thiamine. Thiamine toxicity is characterized by drug fever and anaphylaxis after IV administration of thiamine.
|
|