Vitamin B6: Benefits, Dosage, and Safety

What vitamin b6 is

Vitamin B6 is a water-soluble vitamin naturally present in many foods, added to others, and available as a dietary supplement. It is the generic name for six related compounds (vitamers): pyridoxine, pyridoxal, pyridoxamine, and their respective 5'-phosphate esters. Pyridoxal 5'-phosphate (PLP) and pyridoxamine 5'-phosphate (PMP) are the active coenzyme forms. It is absorbed by passive diffusion in the jejunum.

What it does

• Acts as a coenzyme in more than 100 enzyme reactions, mostly involved in protein metabolism
• Supports amino acid metabolism (both PLP and PMP) and the metabolism of one-carbon units, carbohydrates, and lipids (PLP)
• Contributes to cognitive development through the biosynthesis of neurotransmitters
• Helps maintain normal blood levels of homocysteine
• Involved in gluconeogenesis and glycogenolysis
• Supports immune function, for example by promoting lymphocyte and interleukin-2 production
• Involved in hemoglobin formation

How much vitamin b6 per day

These are population reference values from the NIH and the Dietary Reference Intakes. They are targets for healthy people, not personal prescriptions. The last column is the Tolerable Upper Intake Level, the most you should get from all sources combined.

Deficiency and who is at risk

Isolated vitamin B6 deficiency is uncommon and usually occurs alongside low levels of other B-complex vitamins such as vitamin B12 and folic acid. Deficiency is associated with microcytic anemia, electroencephalographic abnormalities, dermatitis with cheilosis (scaling on the lips and cracks at the corners of the mouth) and glossitis (swollen tongue), depression and confusion, and weakened immune function. In infants it can cause irritability, abnormally acute hearing, and convulsive seizures. People with borderline or mild deficiency may have no signs for months or years.

Who may need more

• People with impaired renal function or on kidney dialysis
• People with autoimmune disorders such as rheumatoid arthritis
• People with malabsorption syndromes (celiac disease, Crohn's disease, ulcerative colitis)
• People with alcohol dependence
• People taking certain medications (antiepileptics, cycloserine, theophylline)

Food sources

Richest sources include fish, beef liver and other organ meats, potatoes and other starchy vegetables, and non-citrus fruit. Examples per serving: canned chickpeas (1 cup, 1.1 mg), pan-fried beef liver (3 oz, 0.9 mg), fresh yellowfin tuna (3 oz, 0.9 mg), sockeye salmon (3 oz, 0.6 mg), roasted chicken breast (3 oz, 0.5 mg), fortified breakfast cereals (0.4 mg), boiled potatoes (1 cup, 0.4 mg), and a medium banana (0.4 mg). About 75% of vitamin B6 from a mixed diet is bioavailable.

Forms and absorption

Vitamin B6 is available in multivitamins, in B-complex supplements, and as a stand-alone supplement. The most common form in supplements is pyridoxine (as pyridoxine hydrochloride, pyridoxine HCl), although some contain pyridoxal 5'-phosphate (PLP). It comes in oral capsules or tablets (including sublingual and chewable) and liquids. Absorption from supplements is similar to that from food and does not differ substantially among the various forms. The body absorbs large pharmacological doses well but quickly eliminates most of the vitamin in urine.

Safety, excess and interactions

Too much

High intakes of vitamin B6 from food sources have not been reported to cause adverse effects. However, chronic use of 1 to 6 g of oral pyridoxine per day for 12 to 40 months can cause severe and progressive sensory neuropathy characterized by ataxia (loss of control of bodily movements). Severity appears dose dependent, and symptoms usually stop when supplements are discontinued as soon as neurologic symptoms appear. Other reported effects of excessive intake include painful, disfiguring dermatological lesions, photosensitivity, and gastrointestinal symptoms such as nausea and heartburn.

Interactions to know

• Cycloserine (Seromycin), an antibiotic for tuberculosis: increases urinary excretion of pyridoxine and can exacerbate seizures and neurotoxicity; pyridoxine supplements can help prevent these effects
• Antiepileptic drugs valproic acid (Depakene, Stavzor), carbamazepine (Carbatrol, Epitol, Tegretol), and phenytoin (Dilantin): increase the catabolism of vitamin B6 vitamers, lowering plasma PLP and raising homocysteine
• Pyridoxine supplementation (200 mg/day for 12-120 days) can reduce serum concentrations of phenytoin and phenobarbital, possibly by increasing their metabolism
• Levetiracetam (Keppra): vitamin B6 (50-350 mg/day in children, 50-100 mg/day in adults) may reduce its behavioral side effects such as irritability, agitation, and depression, per preliminary evidence
• Theophylline (Aquaphyllin, Elixophyllin, Theolair, Truxophyllin): treated patients often have low plasma PLP, which may contribute to neurological and CNS side effects including seizures

How status is measured

Vitamin B6 status is most commonly measured as plasma pyridoxal 5'-phosphate (PLP). PLP above 30 nmol/L has traditionally indicated adequate status, while the Food and Nutrition Board used 20 nmol/L as the major indicator of adequacy when setting the adult RDAs. Status can also be assessed by measuring other vitamers or total vitamin B6 in plasma, erythrocytes, or urine, or indirectly via erythrocyte aminotransferase saturation by PLP or tryptophan metabolites.

Regulated by the FDA as a dietary supplement ingredient under DSHEA, not as a drug; supplements are not FDA-approved to diagnose, treat, cure, or prevent disease. The FDA Daily Value (DV) for vitamin B6 is 1.7 mg for adults and children age 4 years and older.

What the evidence supports

We grade the strength of evidence behind each common reason people take vitamin b6, mirroring how the NIH describes it.