Vitamin B1 (thiamin)
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The first of the B-vitamins to be discovered; water-soluble and like other B-vitamins, it is not appreciably stored and, therefore, must be supplied daily; required by every cell in the body to make ATP - the fuel and energy source for the body; helps convert carbohydrates into energy; produces hydrochloric acid which aids in digestion; metabolizes fats and proteins; plays a major role in the conversion of blood sugar (glucose) into biological energy; necessary for the maintenance of nerve function, nerve tissues and nerve transmission; important for the maintenance of muscular function, especially the heart; and is required for the synthesis of acetylcholine which is the primary neurotransmitter involved in memory and thought processes. In addition, beriberi is the classical B1 deficiency syndrome, resulting from a vitamin B1 deficiency. It is more prevalent in Asian countries where polished rice is the staple diet. When beriberi occurs in the U.S., it is most commonly seen in severely malnourished infants and elderly people.

A vitamin B1 deficiency could be a contributing cause of alcoholism, anorexia, beriberi, chronic dieting, constipation, depression, edema, fatigue, heart palpitation, impaired muscular coordination, indigestion, irritability, loss of appetite, loss of energy, loss of memory, loss of reflexes in legs, mental confusion, muscle weakness, nerve damage (numbness and tingling of the hands and/or feet), psychological stress, rapid pulse rate, sore calf muscles and weight loss. Low blood pressure and dizziness are also possible symptoms of a vitamin B1 deficiency. A U.S. Department of Agriculture study reports that vitamin B1 is one of the most common nutritional deficiencies, with 45% of Americans consuming less than the RDA. In addition, alcohol interferes with the absorption of vitamin B1 and the vitamin is also necessary for the metabolism of alcohol. Severe deficiency associated with alcohol consumption produces a condition known as Wernicke-Korsakoff Syndrome, with symptoms ranging from mild confusion to severely impaired cognitive function, memory function and coma.

Pharmaceutical drugs that can cause a vitamin B1 deficiency include aminoglycosides, bumetanide, cephalosporins, chlortetracycline, demeclocycline, doxycycline, ethacrynic acid, fluoroquinolones, furosemide, macrolides, minocycline, oxytetracycline, penicillins, phenytoin, sulfonamides, tetracyclines, torsemide and trimethoprim.

Dietary sources richest in vitamin B1 (per serving) include brewer's yeast, enriched grains and grain products, legumes (beans, lentils, peas, soybeans), nutritional supplements, nutritional yeasts, organ meats, pork, rice bran and wheat germ. Excessive ingestion of certain raw fresh-water fish and shellfish, blueberries, coffee, red cabbage and tea should be avoided, as these foods may contain anti-thiamin factors. In addition, vitamin B1 is easily destroyed or lost during cooking because it is heat-sensitive and water-soluble.