Clinician Fact Sheet: The B Vitamins: Part II
March 1, 2001
Clinician Fact Sheet: The B Vitamins: Part II
Vitamin B3 (niacin, nicotinic acid, and nicotinate)
March 2001; Volume 4; S1-S2
Severe vitamin B3 deficiency is known as pellagra and is characterized by dermatitis, dementia, and diarrhea. Pellagra is limited to areas where nutrition is severely limited and based on corn.
Dietary Reference Intakes (DRI)
- 2 mg/d for children 0-6 mo 4 mg/d for children 6 mo-1 y
- 6 mg/d for children 1-3 y 8 mg/d for children 4-8 y
- 12 mg/d for children 9-13 y 16 mg/d for men 14 y and older
- 14 mg/d for women 14 y and older
Food Sources
- Both niacin and one of its precursors, tryptophan, are considered when determining niacin food content.
- Dietary sources of niacin and tryptophan include lean meats, poultry, fish, peanuts, organ meats, brewer’s yeast, milk, legumes, and some cereals, especially enriched grains and flours.
- Niacin also is synthesized by intestinal bacteria.
Mechanism of Action
- Vitamin B3 functions as a component of the pyridine nucleotides: nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP).
- NAD and NADP are involved in more than 200 different reactions in the metabolism of carbohydrates, fatty acids, and amino acids.
- Important in the oxidation-reduction reactions in the Krebs cycle involving the production of energy from carbohydrates.
- Critical for the step-wise transfer of electrons in mitochondria.
- Has been shown to have anti-anxiety activity resembling benzodiazepines.
- Has been identified as part of the glucose tolerance factor of yeast which enhances response to insulin.
Clinical Uses
- To treat elevated blood cholesterol levels, reducing LDL and triglycerides and increasing HDL.
- At dosages of about 2 g/d, to reduce the recurrence rate for heart attacks by 30% and overall mortality by 11%.
- To prevent the development of diabetes in high-risk children.
- To preserve residual beta-cell function and improve glycemic control in adult diabetics.
- To improve flexibility and reduce inflammation in osteoarthritics.
- To reduce benzodiazepine withdrawal.
- To reduce the occurrence of cataracts.
- To control fluid loss caused by cholera.
Adverse Effects/Toxicity
- Naturally occurring niacin in food causes no known adverse effects.
- Large doses may cause transient side effects (e.g., tingling sensations, flushing of the skin, and head throbbing), which subside within 20-30 minutes and usually disappear entirely with continued use.
- Sustained release forms of vitamin B3 may be hepatotoxic, and should be avoided if possible and used only with physician supervision.
- Chronic use of large amounts has been associated with rash, hyperpigmentation, dry skin, xerostomia, hyperuricemia, gout, peptic ulcer, amblyopia, proptosis, nervousness, panic, hyperglycemia, abnormal glucose tolerance and glycosuria, hepatotoxicity, abnormal prothrombin times, and hypoalbuminemia.
- Higher doses can cause significant increases in homocysteine levels.
Interactions/Nutrient Depletion
- Drugs that deplete vitamin B3 include: aminoglycosides, cephalosporins, chlortetracycline, demeclocycline, doxycycline, fluoroquinolones, isoniazid, macrolides, minocycline, oxytetracycline, penicillins, sulfonamides, tetracyclines, and trimethoprim.
- Symptoms of deficiency include cracked, scaly dermatitis, especially on those areas exposed to the sun; inflammation of the mucous membranes of the GI tract, causing swollen tongue and diarrhea; and mental confusion and disorientation, leading to psychosis or delirium.
Vitamin B5 (pantothenic acid)
Vitamin B5 is involved in a number of essential metabolic roles including the production of some hormones and neurotransmitters, as well as the metabolism of all carbohydrates, fats, and proteins. Upon absorption, vitamin B5 first is converted to a sulfur-containing compound called pantetheine, then into co-enzyme A (CoA), the only known biologically active form of vitamin B5. Vitamin B5 is present in so many foods that deficiency in humans is virtually unknown. Experimentally induced deficiencies present as skin, liver, thymus, and nervous disorders.
Dietary Reference Intakes (DRI)
- 1.7 mg/d for children 0-6 mo
- 1.8 mg/d for children 6 mo-1 y
- 2 mg/d for children 1-3 y
- 3 mg/d for children 4-8 y
- 4 mg/d for children 9-13 y
- 5 mg/d for men and women 14 y and older
Food Sources
Vitamin B5 is present in all plant and animal tissues. Good dietary sources include eggs, liver, fish, chicken, whole grain breads, cereals, legumes, cauliflower, broccoli, lean beef, white and sweet potatoes, and tomatoes.
Mechanism of Action
- As a constituent of CoA, vitamin B5 participates in a wide variety of enzymatic reactions.
- CoA is involved in the release of energy from carbohydrates in the Krebs cycle.
- CoA is necessary for the synthesis of steroid hormones and proper functioning of the adrenal glands.
- CoA also functions in the production of fats, cholesterol, and bile acids.
- Vitamin B5 is necessary for the synthesis of acetylcholine, phospholipids, and porphyrin in the hemoglobin of red blood cells.
Clinical Uses
- To boost energy and athletic ability.
- To detoxify alcohol.
- To improve the stress reactions of well-nourished individuals.
- To relieve the "burning feet" syndrome of diabetic neuropathy.
- To decrease cholesterol (pantetheine form only).
- To decrease the symptoms of rheumatoid arthritis in a subset of patients.
Adverse Effects/Toxicity
- There are no known toxic effects.
- Large doses may cause diarrhea.
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.
March 2001; Volume 4; S1-S2
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