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Vitamin B6

Definition

Vitamin B6 is a water-soluble organic compound that the body needs to remain healthy. Humans cannot make vitamin B6, so they must get it from foods in their diet. Vitamin B6 is sometimes called pyridoxine.

Purpose

Vitamin B6 has a broad range activities and is necessary for the correct functioning of many systems in the body. It plays a role in the transmission of nerve impulses, formation and functioning of red blood cells, formation of new cells skin and other cells, and conversion of stored carbohydrates into energy. It aids in the production of DNA (genetic material) and, along with vitamin B12 and folic acid (vitamin B9), it helps regulate the levels of an amino acid (homocysteine) in the blood thought to be linked to heart disease.

Description

Vitamin B6 is not a single compound. It has three different forms: pyrodoxine, pyridoxal, pyridoxamine, and three derivatives of these forms. All forms of vitamin B6 are converted in the body into the same active molecule, pyridoxal 5'-phosphate (PLP). Vitamin B6 is a water-soluble vitamin. Unlike the fat-soluble vitamins A, D, E, and K, it is not stored in the body but is excreted in urine.

Vitamin B6

AgeRecommended Dietary Allowance (mg)Tolerable Upper Intake Level (mg)
Children 0–6 mos.0.1 (AI)Not established
Children 7–12 mos.0.3Not established
Children 1–3 yrs.0.530
Children 4–8 yrs.0.640
Children 9–13 yrs.1.060
Boys 14–18 yrs.1.380
Girls 14–18 yrs.1.280
Adults 19–50 yrs.1.3100
Men 51>yrs.1.7100
Women 51>yrs.1.5100
Pregnant women1.9100
Breastfeeding women2.0100
FoodVitamin B6 (mg)
Cereal, 100% fortified, ¾ cup2.0
Potato, baked, med. with skin0.70
Banana, 1 med.0.68
Chicken or turkey breast, roasted, 4 oz.0.64
Cod, baked or broiled, 4 oz.0.52
Salmon, baked or broiled, 4 oz.0.52
Cereal, 25% fortified, ¾ cup0.50
Beef tenderloin, lean, 4 oz.0.49
Halibut, baked or broiled, 4 oz.0.45
Pork loin, lean, 3 oz.0.42
Spinach, fresh, cooked, ½ cup0.22
Watermelon, 1 cup0.22
Carrots, raw, 1 cup0.18
Tuna, canned, 3 oz.0.18
Green peas, ½ cup0.17
Peanut butter, smooth, 2 tbsp.0.15
Spinach, frozen, cooked, ½ cup0.14
AI = Adequate Intake 
mg = milligram 

(Illustration by GGS Information Services/Thomson Gale.)

Normal vitamin B6 requirements

The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for vitamins and minerals. The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97–98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.

The IOM has not set RDA or UL values for vitamin B6 in children under one year old because of incomplete scientific information. Instead, it has set

KEY TERMS

Amino acid—Molecules that are the basic building blocks of proteins.

Coenzyme—Also called a cofactor, a small non-protein molecule that binds to an enzyme and catalyzes (stimulates) enzyme-mediated reactions.

Conventional medicine—Mainstream or Western pharmaceutical-based medicine practiced by medical doctors, doctors of osteopathy, and other licensed health care professionals.

Dietary supplement—A product, such asa vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual's diet with the expectation that it will improve health.

Enzyme—A protein that change the rate of a chemical reaction within the body without themselves being used up in the reaction.

Neurotransmitter—A chemical released by a nerve cell that transmits information to another cell.

Vitamin—A nutrient that the body needs in small amounts to remain healthy but that the body cannot manufacture for itself and must acquire through diet.

Water-soluble vitamin—A vitamin that dissolves in water and can be removed from the body in urine.

AI levels for this age group. AI and RDA levels are measured in milligrams (mg).

The following are the RDAs and ULs for vitamin B6 for healthy individuals:

  • children birth–6 months: AI 0.1 mg; UL not established
  • children 7–12 months: 0.3 mg; UL not established
  • children 1–3 years: 0.5 mg; UL 30 mg
  • children 4–8 years: 0.6 mg; UL 40 mg
  • children 9–13 years: 1.0 mg; UL 60 mg
  • boys 14–18 years: 1.3 mg; UL 80 mg
  • girls 14–18 years: 1.2 mg; UL 80 mg
  • adults 19–50 years: 1.3 mg; UL 100 mg
  • men age 51 and older: 1.7 mg; UL 100 mg
  • women age 51 and older: 1.5 mg; UL 100 mg/item
  • pregnant women: 1.9 mg; UL 100 mg
  • breastfeeding women: 2.0 mg; UL 100 mg

Sources of vitamin B6

Vitamin B6 is found in many foods including meat, milk, potatoes, dark green vegetables, fortified breakfast cereals and fortified grains and flour. Heating and freezing foods reduces their vitamin B6 content. As much as 60–80% of the vitamin B6 in vegetables is lost when they are canned, and about 40% is lost in canned fruit. Processing grains and meat also causes the loss of vitamin B6.

The following list gives the approximate vitamin B6 content for some common foods:

  • spinach, fresh, cooked, 1/2 cup: 0.22 mg
  • spinach, frozen, cooked 1/2 cup: 0.14 mg
  • potato, baked, medium with skin: 0.70 mg
  • carrots, raw 1 cup: 0.18 mg
  • green peas, 1/2 cup: 0.17 mg
  • peanut butter, smooth, 2 Tablespoons: 0.15 mg
  • banana, 1 medium: 0.68 mg
  • watermelon, 1 cup: 0.22 mg
  • salmon, baked or broiled, 4 ounces: 0.52 mg
  • cod, baked or broiled, 4 ounces: 0.52 mg
  • halibut, baked or broiled, 4 ounces: 0.45 mg
  • tuna, canned, 3 ounces: 0.18
  • chicken or turkey breast, roasted, 4 ounces: 0.64
  • pork loin, lean, 3 ounces: 0.42 mg
  • beef tenderloin, lean, 4 ounces: 0.49 mg
  • breakfast cereal, 3/4 cup, fortified 100%: 2.0 mg
  • breakfast cereal, 3/4 cup, fortified 25%: 0.5 mg

Vitamin B6's role in health

Vitamin B6 was discovered in the 1930s and is one of the best studied of the vitamins. Few vitamins and minerals have such a broad and diverse range of activity in the body.

VITAMIN B6 AS A COENZYME. Enzymes are proteins that regulate chemical reactions within the body. Coenzymes are molecules that join with enzymes making it possible for reactions to take place. Vitamin B6 has been identified as being involved in more than 100 enzyme reactions. Some of these reactions include:

  • making neurotransmitters. Neurotransmitters are molecules that carry information from one nerve to the next. Vitamin B6 is directly involved in the formation of the neurotransmitter serotonin in the brain and indirectly involved in the production the neurotransmitters dopamine, epinephrine, norepinephrine, melatonin, and gamma-aminobutyric acid (GABA). Inadequate amounts of these neurotransmitters are associated with mood changes such as depression and poor functioning of the nervous system.
  • hemoglobin function. Hemoglobin is the molecule in red blood cells that carries oxygen throughout the body. Vitamin B6 appears to increase the efficiency of hemoglobin, although the how this happens is not clear.
  • using stored glycogen. Glycogen is a special carbohydrate stored in the liver and in muscles. Physical activity causes glycogen to be broken down into glucose (sugar) that is used for energy. Vitamin B6 is one of several B vitamins that are essential to this process.
  • making new nucleic acids. DNA, the protein that genes are made of, and RNA, a related protein, are made of nucleic acids. Whenever cells divide to form new cells, more DNA and RNA are needed. Because vitamin B6 is needed to create nucleic acids, it plays a role in cell division and wound healing.
  • turning genes on and off. Vitamin B6 joins with other molecules to activate and inactivate different genes. The exact mechanism by which this takes place is unclear.
  • regulation of homocysteine. Increased levels of homocysteine, an amino acid that is released when protein is broken down, appears to be associated with increased damage to blood vessels and increased risk of heart disease. Vitamin B6, probably working with folic acid and vitamin B12, lowers the level of homocysteine in the blood. However, large doses of B6 alone do not appear to reduce heart disease.

Other health claims have also been proposed for vitamin B6. These include relieving premenstrual symptoms, boosting the immune system, improving mental functioning in the elderly, decreasing the likelihood of developing kidney stones, treating depression, treating carpal tunnel syndrome, treating morning sickness in pregnant women, treating drug-induced movement disorders in people with schizophrenia, treating attention deficit-hyperactivity disorder (ADHD) in children and treating autism. None of the studies done using vitamin B6 to treat these disorders have produced conclusive results that satisfy the practitioners of conventional medicine. Clinical trials are currently underway to determine safety and effectiveness of vitamin E in a variety of situations. Individuals interested in participating in a clinical trial at no charge can find a list of open trials at <http://www.clinicaltrials.gov>

Vitamin B6 deficiency

Vitamin B6 deficiency is uncommon in the United States. It can result from a few rare genetic disorders. People with alcoholism are at higher risk for developing vitamin B6 deficiency, as are the elderly and people taking certain prescription drugs (see Interactions below). Internationally, malnutrition and lack of a varied diet are the greatest causes of vitamin B6 deficiency. Symptoms are slow to appear and include skin inflammation, inflammation of the tongue, ulcers in the mouth, irritability, depression, and confusion. These symptoms have many other causes besides vitamin B6 deficiency and should be evaluated by a physician.

Precautions

Few precautions are necessary when taking vitamin B6, although pregnant and breastfeeding women should avoid taking large amounts as a dietary supplement. Even at high doses, few side effects are reported, but include nausea, vomiting, and breast soreness. Very high doses (above 200 mg/day) taken over a long period can result in loss of feeling in the arms and legs and problems with balance. These symptoms usually go away after several months when vitamin B6 supplementation is stopped. The UL is 50 times higher than the RDA, but no health benefits have been confirmed from taking large daily supplements of vitamin B6.

Interactions

Vitamin B6 reduces the effectiveness of tetracy-cline antibiotics, the seizure drug phenytoin, and lev-odopa used to treat Parkinson's disease.

Tuberculosis drugs cycloserine and isoniazid (INH), penicillamine (used to treat rheumatoid arthritis) and theophylline (used to treat asthma) reduce the level of vitamin B6 in the blood. Vitamin B6 supplementation may be required on he advice of a physician

Interactions with herbal remedies are unknown.

Complications

No complications are expected when vitamin B6 is used in the recommended amounts. The complications resulting from insufficient or excess use are discussed above.

Parental concerns

Parents should be aware that the RDA and UL for vitamins and minerals are much lower for children than for adults. Accidental overdose may occur if children are given adult vitamins or dietary supplements.

BOOKS

Berkson, Burt and Arthur J. Berkson. Basic Health Publications User's Guide to the B-complex Vitamins. Laguna Beach, CA: Basic Health Publications, 2006.

Lieberman, Shari and Nancy Bruning. The Real Vitamin and Mineral Book: The Definitive Guide to Designing Your Personal Supplement Program, 4th ed. New York: Avery, 2007.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals, 3rd ed. Indianapolis, IN: Alpha Books, 2007.

Rucker, Robert B., ed. Handbook of Vitamins. Boca Raton, FL: Taylor & Francis, 2007.

ORGANIZATIONS

American Cancer Society. 1599 Clifton Road NE, Atlanta GA 30329–4251. Telephone: 800 ACS–2345. Website: <http://www.cancer.org>

American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, Illinois 60606–6995. Telephone: (800) 877–1600. Website: <http://www.eatright.org>

Linus Pauling Institute. Oregon State University, 571 Weniger Hall, Corvallis, OR 97331–6512. Telephone: (541) 717–5075. Fax: (541) 737–5077. Website: <http://lpi.oregonstate.edu>

Office of Dietary Supplements, National Institutes of Health. 6100 Executive Blvd., Room 3B01, MSC 7517, Bethesda, MD 20892–7517 Telephone: (301)435–2920. Fax: (301)480–1845. Website: <http://dietary-supplements.info.nih.gov>

OTHER

American Cancer Society “Vitamin B Complex.” American Cancer Society, October 6, 2005. <http://www.cancer.org/docroot/ETO/content/ETO_5_3X_Vitamin_B6.asp?sitearea=ETO>

Frye, Richard E. “Pyridoxine Deficiency.” emedicine.com, July 11, 2006. <http://www.emedicine.com/med/topic1977.htm>

Higdon, Jane. “Vitamin B6.”Linus Pauling Institute-Oregon State University, February 19, 2002. <http://lpi.oregonstate.edu/infocenter/vitamins/VitaminB6>.

Harvard School of Public Health. “Vitamins.” Harvard University, November 10, 2006. <http://www.hsph.harvard.edu/nutritionsource/vitamins.html>

Maryland Medical Center Programs Center for Integrative Medicine. “Vitamin B6 (Pyridoxine).” University of Maryland Medical Center, April 2002. <http://www.umm.edu/altmed/ConsSupplements/VitaminB6Pyroxidinecs.html>

Medline Plus. “Vitamin B6.” U. S. National Library of Medicine, September 1, 2006. <http://www.nlm.nih/gov/medlineplus/druginfo/natural/patient-B6.html>.

Office of Dietary Supplements. “Dietary Supplement Fact Sheet: Vitamin B6.” National Institutes of Health, January 11, 2007. http://ods.od.nih.gov/factsheets/vitamindB6asp/.

Tish Davidson, A.M.


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