tailieunhanh - Chapter 071. Vitamin and Trace Mineral Deficiency and Excess (Part 3)

Thiamine (Vitamin B1) Thiamine was the first B vitamin to be identified and is therefore also referred to as vitamin B1. Thiamine functions in the decarboxylation of αketoacids, such as pyruvate α-ketoglutarate, and branched-chain amino acids and thus is a source of energy generation. In addition, thiamine pyrophosphate acts as a coenzyme for a transketolase reaction that mediates the conversion of hexose and pentose phosphates. It has also been postulated that thiamine plays a role in peripheral nerve conduction, although the exact chemical reactions underlying this function are unknown. Food Sources The median intake of thiamine in the United States from. | Chapter 071. Vitamin and Trace Mineral Deficiency and Excess Part 3 Thiamine Vitamin B1 Thiamine was the first B vitamin to be identified and is therefore also referred to as vitamin B1. Thiamine functions in the decarboxylation of a-ketoacids such as pyruvate a-ketoglutarate and branched-chain amino acids and thus is a source of energy generation. In addition thiamine pyrophosphate acts as a coenzyme for a transketolase reaction that mediates the conversion of hexose and pentose phosphates. It has also been postulated that thiamine plays a role in peripheral nerve conduction although the exact chemical reactions underlying this function are unknown. Food Sources The median intake of thiamine in the United States from food alone is 2 mg d. Primary food sources for thiamine include yeast organ meat pork legumes beef whole grains and nuts. Milled rice or grains contain little thiamine if any. Thiamine deficiency is therefore more common in cultures that rely heavily on a rice-based diet. Tea coffee regular and decaffeinated raw fish and shellfish contain thiaminases which can destroy the vitamin. Thus drinking large amounts of tea or coffee can theoretically lower thiamine body stores. Deficiency Most dietary deficiency of thiamine worldwide is the result of poor dietary intake. In Western countries the primary causes of thiamine deficiency are alcoholism and chronic illness such as cancer. Alcohol interferes directly with the absorption of thiamine and with the synthesis of thiamine pyrophosphate. Thiamine should always be replenished when refeeding a patient with alcoholism as carbohydrate repletion without adequate thiamine can precipitate acute thiamine deficiency. Other at-risk populations are women with prolonged hyperemesis gravidarum and anorexia patients with an overall poor nutritional status on parenteral glucose and patients on chronic diuretic therapy due to increased urinary thiamine losses. Maternal thiamine deficiency can lead to infantile beriberi in

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