Clinician Fact Sheet: The B Vitamins: Part III
Clinician Fact Sheet: The B Vitamins: Part III
Vitamin B6 (pyridoxine)
April 2001; Volume 4; S1-S2
Necessary for the proper functioning of more than 60 enzymes, many vitamin b6 activities are related to the metabolism of amino acids and other protein-related compounds. Inside a cell, vitamin B6 is phosphorylated, converting it to its active form, pyridoxal phosphate (PLP).
Dietary Reference Intakes (DRI)
- 0.1 mg/d for children 0-6 mo 1.3 mg/d for men 14-50 y
- 0.3 mg/d for children 6 mo-1 y 1.7 mg/d for men 51 y and older
- 0.5 mg/d for children 1-3 y 1.2 mg/d for women 14-18 y
- 0.6 mg/d for children 4-8 y 1.3 mg/d for women 19-50 y
- 1.0 mg/d for children 9-13 y 1.5 mg/d for women 51 y and older
Food Sources
Dietary sources of vitamin B6 include brewer’s yeast, wheat germ, organ meats, peanuts, legumes, potatoes, and bananas. Vitamin B6 also is synthesized by friendly intestinal bacteria.
Mechanism of Action
• Pyridoxal phosphate is involved with amino acid metabolism, hemoglobin formation, red blood cell growth, tryptophan synthesis and conversion, and neurotransmitter production.
• Pyridoxal phosphate facilitates glycogen conversion to glucose.
Clinical Uses
- To treat hereditary sideroblastic anemia and other macrocytic anemias.
- To treat certain metabolic disorders, including xanthurenic aciduria, primary cystathioninuria, primary hyperoxaluria, and primary homocystinuria.
- To treat depression.
- To treat premenstrual syndrome, including symptoms associated with oral contraceptives.
- To treat pregnancy-induced nausea and vomiting.
- To prevent atherosclerosis by metabolizing homocysteine.
- To treat chronic fatigue syndrome.
- To correct alcohol-related B6 deficiency.
- To prevent and treat repetitive motion injuries such as carpal tunnel syndrome.
- To relieve arthritis symptoms.
- To reduce the risk of recurring kidney stones.
- To treat seborrheic dermatitis.
- To treat children with attention deficit hyperactivity disorder.
Adverse Effects/Toxicity
• Vitamin B6 can cause nausea, vomiting, abdominal pain, loss of appetite, headache, paresthesia, somnolence, increased serum AST, decreased serum folic acid levels, allergic reactions, breast tenderness and enlargement, and photosensitivity.
• Large doses (1-6 g/d) can be neurotoxic. Symptoms can include tingling in the hands and feet, decreased muscle coordination, and stumbling gait. Limited and inconsistent toxicity evidence with doses of 500 mg/d. No toxicity has been reported with 100-300 mg/d; a safe upper limit is considered 100 mg/d.
Interactions/Nutrient Depletion
• Drugs that deplete vitamin B3 include: aminoglycosides, bumetanide, cephalosporins, chlortetracycline, demeclocycline, diethylstilbestrol, doxycycline, conjugated and esterified estrogens, ethacrynic acid, fluoroquinolones, furosemide, hydralazine, hydrochloro-thiazide, isoniazid, macrolides, minocycline, oral contraceptives, oxytetracycline, penicillamine, penicillins, quinestrol, raloxifene, sulfonamides, tetracyclines, theophylline, torsemide, and trimethoprim.
• Drug combinations that can deplete vitamin B6 levels include: hydralazine and hydrochlorothiazide; hydra-lazine, hydrochlorothiazide, and reserpine; and hydro-chlorothiazide and triamterene.
• Deficiencies manifest as dermatologic, circulatory, and neurologic disorders. Symptoms include depression, sleep disturbances, nerve inflammation, premenstrual syndrome, lethargy, decreased alertness, anemia, altered mobility, elevated homocysteine, nausea, vomiting, and seborrheic dermatitis.
Vitamin B12 (cobalamin)
Vitamin B12 is an essential growth factor that plays a role in the metabolism of cells, particularly those of the gastrointestinal tract, bone marrow, and nervous tissues. Although it is water-soluble, relatively large amounts can be stored in the liver. Vitamin B12 absorption is facilitated by intrinsic factor, a protein in gastric secretions, without which absorption drops to less than 1%.
Dietary Reference Intakes (DRI)
- 0.4 mcg/d for children 0-6 mo
- 0.5 mcg/d for children 6 mo-1 y
- 0.9 mcg/d for children 1-3 y
- 1.2 mcg/d for children 4-8 y
- 1.8 mcg/d for children 9-13 y
- 2.4 mcg/d for men and women 14 y and older
Food Sources
Dietary sources of vitamin B12 include organ meats, clams, oysters, beef, eggs, milk, chicken, and cheese.
Mechanism of Action
• Vitamin B12 is required for genetic code replication, myelin (the insulation around nerves) synthesis, methionine synthesis, folic acid metabolism, and red blood cells maturation.
• Vitamin B12 plays a role in the metabolism of protein, fat, and carbohydrates.
Clinical Uses
- To treat pernicious anemia.
- To maintain proper functioning of the nervous system.
- To prevent mouth and throat cancer in smokers.
- To relieve the symptoms of asthma.
Adverse Effects/Toxicity
Large doses of vitamin B12 (> 2 g/d) can be neurotoxic. Symptoms can include tingling in the hands and feet, decreased muscle coordination, and stumbling gait.
Interactions/Nutrient Depletion
• Drugs that deplete vitamin B12 include: aminoglycosides, cephalosporins, chlorotriansene, chlortetracycline, cholestramine resin, cimetidine, colestipol, co-trimoxazole, demeclocycline, doxycycline, famotidine, fluoroquinolones, lansoprazole, macrolides, metformin, minocycline, neomycin, nizatidine, ome-prazole, oral contraceptives, oxytetracycline, penicillins, phenytoin, potassium chloride (timed release), ranitidine hydrochloride, sulfonamides, tetracyclines, trimethoprim, and zidovudine.
• Colchicine and probenecid together can deplete vitamin B12 levels.
• Vitamin B12 deficiency inhibits DNA synthesis, which affects cell growth and repair. Deficiencies manifest primarily as anemia and neurologic disorders. Symptoms include: fatigue, peripheral neuropathy, tongue and mouth irregularities, macrocytic anemia, depression, confusion, memory loss, poor blood clotting and easy bruising, dermatitis and skin sensitivity, loss of appetite, nausea, and vomiting.
• Strict vegetarians, the elderly and those with IBD, especially Crohn’s disease that involves the terminal ileum, are at increased risk of deficiency.
• Intramuscular injection is the the most effective route of administration.
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 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.
April 2001; Volume 4; S1-S2
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