In this article, we describe:
- the major purposes of this specific nutrient in the human body,
- its experimentally confirmed health uses,
- conventional ways to estimate nutrient status,
- nutrient’s toxicities and deficiencies,
- experimentally confirmed and approved levels of the nutrient intake for different demographics,
- dietary sources of the nutrient.
Vitamin B6 is a water-soluble vitamin that is naturally present in many foods. It is the generic name for six compounds (vitamers) with vitamin B6 activity: pyridoxine, an alcohol; pyridoxal, an aldehyde; and pyridoxamine, which contains an amino group; and their respective 5’-phosphate esters. Pyridoxal 5’ phosphate (PLP) and pyridoxamine 5’ phosphate (PMP) are the active coenzyme forms of vitamin B6. Substantial proportions of the naturally occurring pyridoxine in fruits, vegetables, and grains exist in glycosylated forms that exhibit reduced bioavailability.
Vitamin B6 in coenzyme forms performs a wide variety of functions in the body and is extremely versatile, with involvement in more than 100 enzyme reactions, mostly concerned with protein metabolism. Both PLP and PMP are involved in amino acid metabolism, and PLP is also involved in the metabolism of one-carbon units, carbohydrates, and lipids. Vitamin B6 also plays a role in cognitive development through the biosynthesis of neurotransmitters and in maintaining normal levels of homocysteine, an amino acid in the blood. Vitamin B6 is involved in gluconeogenesis and glycogenolysis, immune function (for example, it promotes lymphocyte and interleukin-2 production), and hemoglobin formation.
B Complex vitamins are all water soluble and are not stored very well in the body. Thus, they are needed daily through diet or supplement to support their many functions. Deficiencies of one or more of the B vitamins may occur fairly easily, especially during times of fasting or dieting for weight loss or with diets that include substantial amounts of refined and processed food, sugar, or alcohol.
B complex vitamins are fairly easily digested from food or supplements and then absorbed into the blood, mainly from the small intestine. When the amount of Bs taken exceeds the body’s needs, the excess is easily excreted in the urine, giving it a dark yellow color.
Vitamin B6 concentrations can be measured directly by assessing concentrations of PLP; other vitamers; or total vitamin B6 in plasma, erythrocytes, or urine. Vitamin B6 concentrations can also be measured indirectly by assessing either erythrocyte aminotransferase saturation by PLP or tryptophan metabolites. Plasma PLP is the most common measure of vitamin B6 status.
PLP concentrations of more than 20-30 nmol/L have been used as the major indicator of adequacy to calculate the Recommended Dietary Allowances (RDAs) for adults.
Isolated vitamin B6 deficiency is uncommon; inadequate vitamin B6 status is usually associated with low concentrations of other B-complex vitamins, such as vitamin B12 and folic acid. Vitamin B6 deficiency causes biochemical changes that become more obvious as the deficiency progresses. Autoimmune disorders, alcohol dependence, end-stage renal diseases, chronic renal insufficiency, and other kidney diseases can cause vitamin B6 deficiency. In addition, vitamin B6 deficiency can result from malabsorption syndromes, such as celiac disease, Crohn’s disease, and ulcerative colitis. Certain genetic diseases, such as homocystinuria, can also cause vitamin B6 deficiency. Some medications, such as antiepileptic drugs, can lead to deficiency over time.
Scientists have hypothesized that certain B vitamins (folic acid, vitamin B12, and vitamin B6) might reduce cardiovascular disease risk by lowering homocysteine levels. Some research also has associated low plasma vitamin B6 concentrations with an increased risk of certain kinds of cancer; cognitive decline; premenstrual syndrome; nausea and vomiting in pregnancy.
High intakes of vitamin B6 from food sources have not been reported to cause adverse effects. However, chronic administration of 1–6 g oral pyridoxine per day for 12–40 months can cause severe and progressive sensory neuropathy characterized by ataxia (loss of control of bodily movements).
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Recommended Dietary Allowances (RDAs) for Vitamin B6
|Birth to 6 months||0.1 mg*||0.1 mg*|
|7–12 months||0.3 mg*||0.3 mg*|
|1–3 years||0.5 mg||0.5 mg|
|4–8 years||0.6 mg||0.6 mg|
|9–13 years||1.0 mg||1.0 mg|
|14–18 years||1.3 mg||1.2 mg||1.9 mg||2.0 mg|
|19–50 years||1.3 mg||1.3 mg||1.9 mg||2.0 mg|
|51+ years||1.7 mg||1.5 mg|
* Adequate Intake (AI) as equivalent to the mean intake of vitamin B6 in healthy, breastfed infants
Food Sources of Vitamin B6
Vitamin B6 is found in a wide variety of foods. The richest sources of vitamin B6 include fish, poultry, beef liver and other organ meats, potatoes and other starchy vegetables, fruit (other than citrus), and fortified cereals. About 75% of vitamin B6 from a mixed diet is bioavailable.
Selected Food Sources of Vitamin B6
|Food||Milligrams (mg) per serving||Percent DV*|
|Canned chickpeas, 1 cup||1.1||65|
|Pan fried beef liver, 3 ounces||0.9||53|
|Yellowfin tuna, 3 ounces||0.9||53|
|Sockeye Salmon, cooked, 3 ounces||0.6||35|
|Roasted chicken breast, 3 ounces||0.5||29|
|Fortified breakfast cereals||0.4||25|
|Boiled potatoes, 1 cup||0.4||25|
|Roasted turkey meat, 3 ounces||0.4||25|
|Banana, 1 medium||0.4||25|
|Marinara (spaghetti) sauce, 1 cup||0.4||25|
|Broiled ground beef patty, 3 ounces||0.3||18|
|Toasted plain waffles, 1 waffle||0.3||18|
|Cooked bulgur, 1 cup||0.2||12|
|Cottage cheese, 1 cup||0.2||12|
|Baked winter squash, ½ cup||0.2||12|
|Enriched white rice, cooked, 1 cup||0.1||6|
|Dry-roasted mixed nuts, 1 ounce||0.1||6|
|Seedless raisins, ½ cup||0.1||6|
|Chopped onions, ½ cup||0.1||6|
|Boiled spinach, ½ cup||0.1||6|
|Raw firm tofu, ½ cup||0.1||6|
|Watermelon, 1 cup||0.1||6|
- *DV = Daily Value.
- The DV for is 1.7 mg for adults and children age 4 years and older.
- Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.