Clinical Fact Sheet-The B Vitamins: Part I
Vitamin B1 (thiamin)
February 2001; Volume 4; S1-S2
It is estimated that 45% of americans do not consume adequate amounts of vitamin B1. Deficiencies manifest most commonly as disorders of the neuromuscular, gastrointestinal, and cardiovascular systems. Beriberi is the classic deficiency syndrome and is seen most commonly in Asian countries. In the United States, deficiencies are seen most frequently in severely malnourished infants, the elderly, and adults who diet chronically, suffer alcoholism (Wernicke-Korsakoff syndrome), and eat heavily processed- or refined-food diets.
Dietary Reference Intakes (DRI)
0.2 mg/d for children 0-6 mo 0.9 mg/d for children 9-13 y
0.3 mg/d for children 7-12 mo 1.2 mg/d for men 14 y and older
0.5 mg/d for children 1-3 y 1.0 mg/d for women 14-18 y
0.6 mg/d for children 4-8 y 1.1 mg/d for women 18 y and older
Active Constituents
Vitamin B1 must be phosphorylated to be metabolically active. It combines with two molecules of phosphoric acid to form the important co-enzyme thiamine pyrophosphate (TPP).
Food Sources
All plant and animal foods contain vitamin B1, but in very low concentrations. The richest sources include brewer’s yeast, organ meats, and whole cereal grains. Severe deficiency may require parenteral replacement.
Mechanism of Action
• As co-enzyme TPP, performs oxidative decarboxylation reactions in the Krebs cycle and transketolation reactions in the pentose phosphate shunt.
• Plays a major role in the conversion of glucose into biological energy.
• Necessary for the maintenance of nerve tissues, nerve function, and nerve transmission.
• Necessary for the maintenance and proper functioning of muscles, especially the heart.
• Required for the synthesis of acetylcholine, the primary neurotransmitter involved in thought and memory processes.
• Involved in fatty acid synthesis.
Clinical Uses
• To reduce the occurrence of cataracts.
• To treat diabetic neuropathy.
Adverse Effects/Toxicity
As a water-soluble vitamin, vitamin B1 toxicity is very rare and most likely would require IV or parenteral administration. Overdose would require multiple gram dosages. Rare reports of hypersensitivity can be found in the literature.
Interactions/Nutrient Depletion
• Vitamin B1 is heat sensitive and is destroyed easily during cooking.
• Tea may contain anti-thiamin factors, but this is not a problem in usual food intakes.
• Raw fish may contain microbial thiaminases.
• Vitamin B1 levels are depleted by diuretic drugs and GI conditions such as diarrhea, and malabsorption due to lactose intolerance and celiac disease.
• Alcohol interferes with the absorption of vitamin B1, which is necessary for the metabolism of alcohol.
• Drugs that deplete vitamin B1 include: aminoglycosides, bumetanide, cephalosporins, chlortetracycline, demeclocycline, doxycycline, ethacrynic acid, fluoroquinolones, furosemide, macrolides, minocycline, oxytetracycline, penicillins, phenytoin, sulfonamides, tetracyclines, torsemide, and trimethoprim.
• Deficiency symptoms usually are neurologic (fatigue, depression, irritability, memory loss, mental confusion, loss of reflexes in legs, defective muscular coordination, and nerve inflammation, including "pins and needles" and numbness), cardiovascular (edema, muscular weakness, sore calf muscles, heart palpitations, rapid pulse rate), or gastrointestinal (indigestion, weight loss, and anorexia) in nature.
Vitamin B2 (riboflavin)
Vitamin B2 deficiency most commonly affects the skin, eyes, and mucous membranes of the GI tract. Approximately 34% of Americans consume less than the recommended amounts. Like vitamin B1, infants, alcoholics, and elderly persons on highly processed diets are at greatest risk of vitamin B2 deficiencies.
Dietary Reference Intakes (DRI)
0.3 mg/d for children 0-6 mo
0.4 mg/d for children 6 mo-1 y
0.5 mg/d for children 1-3 y
0.6 mg/d for children 4-8 y
0.9 mg/d for children 9-13 y
1.2 mg/d for men 14 y and older
1.0 mg/d for women 14-18 y
1.1 mg/d for women 19 y and older
Food Sources
Dietary sources of vitamin B2 include liver, milk, dairy products, meats, dark green vegetables, eggs, avocados, oysters, mushrooms, fish (e.g., salmon and tuna), and enriched breakfast cereals.
Mechanism of Action
• Facilitates the metabolism of carbohydrates, fats, and proteins.
• Combines with phosphoric acid to become part of two flavin co-enzymes: flavin mononucleotide (FNfN) and flavin adenine dinucleotide (FAD). FNfN and FAD bind more than 100 flavoprotein enzymes, which catalyze oxidation-reduction reactions in cells.
• Plays a critical role in the conversion of carbohydrates to ATP in the production of energy.
• Has important antioxidant activity by itself and as part of the enzyme glutathione reductase.
• Is necessary for growth and reproduction.
• Is necessary for healthy skin, hair, and nails.
Clinical Uses
• To prevent migraine headaches.
• To reduce the occurrence of cataracts.
Adverse Effects/Toxicity
Vitamin B2 is water-soluble and not appreciably stored in the body. There is no known toxicity.
Interactions/Nutrient Depletion
• Approximately 15% of vitamin B2 is absorbed if taken alone, vs. 60% when taken with food.
• Vitamin B2 is heat stable, but very photosensitive.
• Drugs that deplete vitamin B2 include: acetophena-zine, aminoglycosides, amitriptyline, amoxapine, cephalosporins, chlorpromazine, chlortetracycline, chlomipramine, demeclocycline, desipramine, doxepin, doxycycline, fluoroquinolones, fluphenazine, imipramine, macrolides, mesoridazine, methdilazine, methotrimeprazine, minocycline, nortriptyline, oral contraceptives, oxytetracycline, penicillins, perphena-zine, prochlorperazine, promazine, promethazine, protriptyline, sulfonamides, tetracyclines, thiethylperazine, thioridazine, trifluoperazine, trimethoprim, trimipramine.
• Symptoms of deficiency include dermatologic (cheilosis, seborrheic dermatitis, and angular stomatitis) and ophthalmologic (red, teary, burning, itching, and photosensitive eyes) manifestations.
Resources
Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press; 1999. Available at http://books.nap.edu/books/0309065542/html/index.html. Accessed December 27, 2000.
Pelton R, et al. Drug-Induced Nutrient Depletion Handbook. Hudson, OH: Lexi-Comp; 1999.
Natural Medicines Comprehensive Database [database online]. Stockton, CA: Therapeutic Research Center, Inc., 2000.
Stipanuk MH. Biochemical and Physiological Aspects of Human Nutrition. Philadelphia: W. B. Saunders Co.; 2000.
February 2001; Volume 4; S1-S2
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