Vitamin B6 Definition

Definition

Vitamin B6 is a water-soluble B complex vitamin that is required by the body to remain healthy. Humans cannot make vitamin B6, so they must get it from foods in their diet. Vitamin B6 is also called pyridoxine.

Purpose

Vitamin B6 is a coenzyme or cofactor, meaning that it functions in conjunction with many different enzymes and is necessary for more than 100 different enzyme reactions that are involved in human metabolism. Thus, vitamin B6 has a broad range functions that affect many different bodily systems. It is involved in the metabolism of neurotransmitters that carry the impulses between nerves, and thus is essential for nervous system function. It is involved in the formation of new skin and other cells. It is involved in the conversion of stored carbohydrates into energy and helps keep blood sugar (glucose) within a normal range. Vitamin B6 is required for producing hemoglobin that carries oxygen in red blood cells. It is important for breaking down proteins into amino acids, so that the more protein that is consumed, the higher the vitamin B6 requirement. Vitamin B6 is important for the functioning of the immune system, because it is involved in the production of antibodies for fighting disease. Vitamin B6 is involved in brain development in the fetus and infant. It is important for the production of DNA, the genetic material of all cells, and, along with vitamin B12 and folic acid (vitamin B9), it helps regulate the levels of an amino acid in the blood called homocysteine that may be linked to heart disease.

Vitamin B6

Age

Recommended dietary allowance (mg)

Tolerable upper intake level (mg)

Children 0-6 mos.

0.1 (AI)

Not established

Children 7-12 mos.

0.3 (Al)

Not established

Children 1-3 yrs.

0.5

30

Children 4-8 yrs.

0.6

40

Children 9-13 yrs.

1.0

60

Boys 14-18 yrs.

1.3

80

Girls 14-18 yrs.

1.2

80

Adults 19-50 yrs.

1.3

100

Men 51 ≥ yrs.

1.7

100

Women 51 ≥ yrs.

1.5

100

Pregnant women 18≤ yrs.

1.9

80

Pregnant women 19≥ yrs.

1.9

100

Breastfeeding women 18≤ yrs.

2.0

80

Breastfeeding women 19≥ yrs.

2.0

100

Food

Vitamin B6 (mg)

Cereal, 100% fortified, % cup

2.00 (avg.)

Chickpeas, canned, 1 cup

1.10

Yellowfin tuna, 3 oz.

0.88

White rice, enriched, 1 cup

0.83

Potato, baked, with skin

0.62

Pork chops, bone in, 3 oz.

0.60

Salmon, 3 oz.

0.59

Beef, sirloin, 3 oz.

0.53

Brussels sprouts, frozen, boiled, 1 cup

0.45

Banana

0.43

Sweet potato, baked, with skin

0.42

Trail mix, 1 cup

0.38

Lentils, boiled, 1 cup

0.35

Ground beef, 80/20, 3 oz.

0.31

Peanuts, 1 oz.

0.13

Al = Adequate intake

mg = milligram

SOURCE: Office of Dietary Supplements. National Institutes of Health. “Vitamin B6: Fact Sheet for Health Professionals.” https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional (accessed April 19, 2018).

B6 is unique among vitamins in that either a deficiency or an excess can cause peripheral neuropathy, a condition of nerves outside of the central nervous system that is characterized by muscle weakness, numbness, and pain. Vitamin B6 deficiency can also cause problems with the skin and the blood, including a type of anemia in which there are too few functioning red blood cells.

Description

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 activities in the body as vitamin B6.

There are three different forms of vitamin B6—pyridoxine, pyridoxal, pyridoxamine—and three derivatives of each of these. All forms of vitamin B6 are converted in the body into the same active molecule, pyridoxal 5’-phosphate. Vitamin B is a water-soluble vitamin. Unlike the fat-soluble vitamins A, D, E, and K, it is not stored in the body but rather is excreted in urine.

Normal vitamin B6 requirements

The Institute of Medicine (IOM) of the U.S. National Academy of Sciences has developed dietary reference intake (DRI) values for vitamins and minerals. 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 of the daily requirement 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. These amounts are in milligrams (mg) for vitamin B6:

Sources of vitamin B6

Vitamin B6 is found in many foods including chicken, pork, liver, fish, nuts, milk, potatoes, dark green vegetables, dried beans, avocados, bananas, wheat germ, and whole grains. It may be added to fortified breakfast cereals, breads, flour, and other grains. However, heating and freezing foods reduces their vitamin B6 content. As much as 60%–80% of the vitamin B6 in vegetables is lost during canning, and about 40% of B6 in fruit is lost by canning. Processing of meat and grains also reduces their vitamin B6 content.

Approximate vitamin B6 contents of some common foods include:

Role of vitamin B6 in health

Enzymes are proteins that promote (catalyze) chemical reactions within the body. Coenzymes or cofactors are molecules that are required to join with enzymes for their activity. Some of the more than 100 enzyme reactions that require vitamin B6 include:

KEY TERMS
Adequate intake (AI)—
The daily average intake level of a nutrient that is likely to be adequate for a healthy, moderately active individual, as determined by the U.S. Institute of Medicine.
Amino acids—
The basic building blocks of proteins.
Anemia—
A deficiency in red blood cells, in the hemoglobin component of red blood cells, or in total blood volume.
Coenzyme—
Cofactor; a small molecule, such as vitamin B6, that binds to an enzyme and catalyzes (stimulates) enzyme-mediated reactions.
Dietary supplement—
A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is used in addition to one's diet with the expectation that it will maintain or improve health.
Enriched—
Having some of the nutrients that were lost during processing added back.
Enzyme—
A protein that promotes a chemical reaction within the body.
Folic acid—
Folate; vitamin B9.
Fortified—
Having added nutrients, such as vitamin B6, that do not occur naturally in that food.
Hemoglobin—
A protein in red blood cells that binds oxygen in the lungs and delivers it to the cells of the body.
Homocysteine—
An amino acid that is not usually present in protein and that is turned over with the aid of vitamin B6; high blood levels of homocysteine have been associated with cardiovascular disease.
Neurotransmitter—
A chemical that transmits signals between neurons or nerve cells.
Premenstrual syndrome (PMS)—
An array of symptoms— including anxiety, irritability, depression, fatigue, insomnia, headache, and bloating—that affects some women prior to the onset of menstruation.
Pyridoxal 5’-phosphate—
The active form of pyridoxine or vitamin B6.
Recommended dietary allowance(RDA)—
The approximate amount of a nutrient that should be ingested daily.
Tolerable upper intake level (UL)—
The highest daily intake level of a nutrient that is unlikely to cause adverse health effects in almost all individuals in the general population, as determined by the U.S. Institute of Medicine.
Vitamin B12
A water-soluble, cobalt-containing member of the complex of eight B vitamins that is required for many bodily functions, sometimes in conjunction with vitamin B6 and folic acid.
Water-soluble vitamin—
A vitamin that dissolves in water and is excreted in urine.
Vitamin B6 deficiency

Vitamin B6 deficiency is very rare in the United States, although it is associated with a few rare genetic disorders. Alcoholics are at higher risk for developing vitamin B6 deficiency, as are the elderly and those who take certain medications or who have certain inflammatory disorders. People with kidney disorders or kidney transplants or with autoimmune disorders such as rheumatoid arthritis, celiac disease, Crohn's disease, ulcerative colitis, or inflammatory bowel disease sometimes develop vitamin B6 deficiency. Internationally, malnutrition, lack of a varied diet, or a diet limited to non-enriched grains increases the risk of vitamin B deficiency.

Symptoms of vitamin B6 deficiency develop slowing. They include skin and tongue sores and inflammation, scaly lips, or cracks at the corners of the mouth. Other symptoms include itchy rashes and anemia. Very low levels of vitamin B6 can cause irritability, depression, confusion, and a weakened immune system. Infants with vitamin B6 deficiency may become irritable or develop very sensitive hearing or seizures.

Precautions

The tolerable upper intake levels for vitamin B6 are quite high—approximately 50 times the RDA, although there are no confirmed health benefits from large daily vitamin B6 supplements. Even at high doses of vitamin B6 supplements, few side effects have been reported, although these can include nausea, vomiting, and breast soreness. Very high doses (above 200 mg/day) over a long period can result in numbness in the arms and legs; burning, tingling, or pin-pricking of the hands and feet; problems with balance and coordination; and other sensory changes. These symptoms usually disappear within several months of stopping vitamin B6 supplementation.

QUESTIONS TO ASK YOUR DOCTOR

Interactions

Vitamin B6 reduces the effectiveness of tetracycline antibiotics, of the seizure drug phenytoin, and of levodopa used to treat Parkinson's disease. The tuberculosis drugs cycloserine (Seromycin) and isoniazid and penicillamine used to treat rheumatoid arthritis reduce the level of vitamin B6 in the blood and may require B6 supplementation on the advice of a physician. However, vitamin B6 supplements may interact with cycloserine and worsen any seizures or nerve cell damage caused by the drug. Certain epilepsy drugs may both decrease vitamin B6 levels, and vitamin B6 may reduce the effectiveness of the drugs for controlling seizures. Theophylline, used to treat asthma and other lung diseases, can reduce vitamin B6 levels and cause seizures.

Parental concerns

Parents should be aware that the RDA and UL for vitamins and minerals, including vitamin B6, are much lower for children than for adults. Accidental overdose can occur if children take adult vitamins or dietary supplements.

See also Arthritis diet ; Fertility ; Fertility diet ; Folate ; Vitamins .

Resources

BOOKS

Cohen, Suzy. Drug Muggers: Which Medications Are Robbing Your Body of Essential Nutrients—and Natural Ways to Restore Them. Emmaus, PA: Rodale, 2011.

Herrmann, Wolfgang, and Rima Obeid, eds. Vitamins in the Prevention of Human Diseases. New York: Walter de Gruyter, 2011.

Higdon, Jane, and Victoria J. Drake. An Evidence-Based Approach to Vitamins and Minerals: Health Benefits and Intake Recommendations. 2nd ed. New York: Thieme, 2012.

PERIODICALS

Kloss, Beth A., et al. “PMS Treatment through the Use of CAM.” International Journal of Childbirth Education 27, no. 3 (July 2012): 60–64.

WEBSITES

Frye, Richard E., et al. “Pyridoxine Deficiency.” Medscape. Updated September 15, 2016. http://emedicine.medscape.com/article/124947-overview#showall (accessed April 20, 2018).

Harvard T.H. Chan School of Public Health. “Three of the B Vitamins: Folate, Vitamin B6, and Vitamin B12.” The Nutrition Source, Department of Nutrition, Harvard University. http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/vitamin-b (accessed April 20, 2018).

MedlinePlus. “Vitamin B6.” U.S. National Library of Medicine, National Institutes of Health. https://medlineplus.gov/ency/article/002402.htm (accessed April 20, 2018).

Office of Dietary Supplements. “Dietary Supplement Fact Sheet: Vitamin B6.” National Institutes of Health. https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/ (accessed April 20, 2018).

U.S. Department of Agriculture, National Agricultural Library. “DRI Tables and Application Reports.” Food and Nutrition Information Center. https://www.nal.usda.gov/fnic/dri-tables-and-application-reports (accessed March 15, 2018).

ORGANIZATIONS

Food and Nutrition Information Center, National Agricultural Library, 10301 Baltimore Ave., Rm. 105, Beltsville, MD, 20705, (301) 504-5414, Fax: (301) 504-6409, fnic@ars.usda.gov, http://fnic.nal.usda.gov .

Linus Pauling Institute, Oregon State University, 307 Linus Pauling Science Center, Corvallis, OR, 97331, (541) 737-5075, Fax: (541) 737-5077, lpi@oregonstate.edu, http://lpi.oregonstate.edu/infocenter .

Office of Dietary Supplements, National Institutes of Health, 6100 Executive Boulevard, Room 3B01, MSC 7517, Bethesda, MD, 20892-7517, (301) 435-2920, Fax: (301) 480-1845, ods@nih.gov, http://ods.od.nih.gov .

Tish Davidson, AM
Revised by Margaret Alic, PhD

  This information is not a tool for self-diagnosis or a substitute for professional care.