Vitamin B6 Benefits: What Human Studies Show, Doses and Safety

Vitamin B6 is an essential, water-soluble vitamin that your body needs for protein metabolism, brain chemicals and red blood cells. Human studies point to possible help for nausea in pregnancy and premenstrual syndrome (PMS), but many of those studies are small or low quality. Large trials of B6 for heart disease, cancer prevention and memory have mostly found no benefit. Long-term high supplement doses can damage nerves, and one case report describes this at a low multivitamin dose.

Quick facts

What does the human evidence show for each use?

The summaries below come from the NIH Office of Dietary Supplements fact sheet and the PubMed reviews linked in each section. Rather than ranking by hype, they run from the uses with the most supportive trial data to those where trials found little or nothing. Even the first two have limits. To see why study type matters, read our guides on meta-analyses and systematic reviews and evaluating evidence quality.

Nausea and vomiting in pregnancy

A 2023 systematic review and meta-analysis pooled 18 studies. Eight found benefit with pyridoxine alone, and six found benefit when it was combined with another active ingredient. In the pooled scores, pyridoxine alone and combined treatment both significantly improved nausea (Rhodes score 0.78; PUQE score 0.75). The NIH fact sheet reports that two older placebo-controlled trials found that 30-75 mg of oral pyridoxine per day reduced nausea. It also notes that a Cochrane review could not draw firm conclusions. The fact sheet says randomized trials of B6 plus doxylamine (an antihistamine) were associated with a 70% reduction in nausea and vomiting and fewer hospitalizations. It reports that the American College of Obstetricians and Gynecologists (ACOG) bulletin recommends 10-25 mg of B6 three or four times a day as a first step, adding doxylamine if symptoms persist. The fact sheet advises pregnant women to consult a physician first, because doses could approach the upper limit.

Premenstrual syndrome (PMS)

Per the NIH fact sheet, a meta-analysis of nine published trials with almost 1,000 women found B6 more effective than placebo for PMS symptoms. Most of those studies were small and several had methodological weaknesses. A later double-blind randomized trial in 94 women found that 80 mg of pyridoxine daily for three cycles was associated with statistically significant reductions in symptoms including moodiness, irritability, forgetfulness, bloating and especially anxiety. The fact sheet’s conclusion: it shows promise, but more research is needed before firm conclusions.

Pyridoxine-dependent epilepsy (a rare genetic condition)

This is a medical treatment, not a supplement use. A 2024 systematic review covered 56 studies and 169 newborns with the condition, all treated with pyridoxine. 63.9% became completely seizure-free, but 68.6% had neurodevelopmental delays. Starting pyridoxine immediately at seizure onset was linked to better developmental outcomes. There was no untreated comparison group, so it describes outcomes in treated patients. This condition needs specialist care.

Behavior side effects of levetiracetam (an epilepsy drug)

A 2023 systematic review found seven newer studies: two double-blind randomized trials and five retrospective studies or case series. One trial found a significant improvement with pyridoxine, while the other found no significant difference from placebo. The authors rated the evidence quality as poor and found it insufficient for any firm recommendation. This is not a reason to add anything to, or change, an epilepsy medicine without the prescriber.

Heart disease and stroke

The NIH fact sheet says the research to date provides little evidence that supplemental B6, alone or with folic acid and B12, reduces cardiovascular disease or stroke risk. The idea was that these vitamins lower homocysteine, a blood marker; that is a surrogate outcome, and lowering it did not translate into fewer events in most large trials:

• HOPE 2 (over 5,500 adults with cardiovascular disease, 5 years): B6 50 mg, B12 and folic acid together lowered homocysteine and cut stroke risk by about 25%. There was no B6-only group, so B6’s own effect is unknown.
• A trial in 5,442 women age 42 or older found no effect on cardiovascular disease from the same combination.
• The Norwegian trials (combined analysis, 6,837 patients with ischemic heart disease) included a B6-only group at 40 mg/day and found no benefit on major cardiovascular events.
• A trial after nondisabling stroke (2 years) found no effect on repeat stroke, cardiovascular events or death.

Cancer

A meta-analysis of prospective studies found people with the highest B6 intake had a 20% lower colorectal cancer risk than those with the lowest, according to the NIH fact sheet. That type of study cannot show cause, and the few completed trials, including an analysis of two large Norwegian placebo-controlled trials, found no link between B6 supplements and cancer incidence or mortality. One prospective cohort study, discussed on Wikipedia, linked long-term B6 supplement use above 20 mg/day to higher lung cancer risk in men, especially smokers. A later review said a causal link cannot be confirmed yet.

Memory and thinking

A systematic review of 14 randomized trials found insufficient evidence that B6, alone or with B12 and folic acid, affects cognition in people with normal cognition, dementia or ischemic vascular disease. The review said most studies were low quality. A Cochrane review of short-term B6 (5-12 weeks) found no improvement in cognition or mood. Daily 20 mg changed blood markers of B6 status in healthy older men but not cognition. Observational data link higher B6 levels to better memory scores, but that is an association only.

Rheumatoid arthritis and inflammation

People with rheumatoid arthritis often have low B6, and levels fall as the disease worsens. The NIH fact sheet says this is due to inflammation, and that B6 supplements can normalize B6 levels but do not suppress inflammatory cytokines or lower inflammation markers. No source here shows that B6 itself causes inflammation.

Nerve problems (neuropathy)

A 2023 systematic review of 20 articles found that low B6 can be seen in people with neuropathy, but there is no firm evidence it directly causes it. Studies suggesting improvement with B6 used it only as part of combination treatments, so its therapeutic role cannot be confirmed. The same review found high B6 levels from supplements may cause a sensory neuropathy (see safety below).

What is B6 used for in a B complex or multivitamin?

B6 is sold in multivitamins, in B-complex supplements and on its own. The NIH fact sheet notes that low B6 usually appears together with low B12 and folic acid, which is why the three are often studied together. In the heart trials above, the combination tells you little about B6 alone. In US multivitamin/mineral products, Wikipedia reports typically 2-4 mg of B6 per daily serving, while B6-only products often contain 100 mg.

Does B6 help digestion or bowel movements?

B6 is absorbed in the small intestine (the jejunum), and in its coenzyme forms it works in over 100 enzyme reactions, mostly in protein metabolism, per the NIH fact sheet. That is metabolism, not a treatment for bowel problems. The studies summarized on this page did not test B6 for constipation or bowel movements, so no benefit can be claimed. If you are constipated, a clinician can look for causes; the studies here don’t identify a vitamin lacking in constipation. Digestive disease can lower B6: people with celiac disease, Crohn’s disease and ulcerative colitis tend to have low PLP levels, and low B6 can result from malabsorption.

Is B6 good for diabetes?

The pack has no treatment trials of B6 in diabetes. Wikipedia notes decreased B6 levels in women with type 1 diabetes, and that B6-dependent enzymes take part in glucose production, so deficiency can impair glucose tolerance. That describes biology, not a proven therapy. If you have diabetes and are considering B6, ask your clinician.

What are the symptoms of B6 deficiency, and what lowers B6?

According to the NIH fact sheet, deficiency is associated with:

• Microcytic anemia (small red blood cells)
• Abnormal brain-wave (EEG) readings
• Scaly dermatitis, with scaling on the lips and cracks at the corners of the mouth (cheilosis), and a swollen tongue (glossitis)
• Depression and confusion
• Weakened immune function

In infants it causes irritability, abnormally acute hearing and seizures. Mild deficiency may cause no symptoms for months or years. Isolated deficiency is uncommon in the US. In the 2003-2004 national survey, 11% of B6 supplement users and 24% of non-users had low blood PLP (under 20 nmol/L), with lower levels in women than men, current smokers, underweight people and teenagers.

Things linked to low B6 in the sources:

• Alcohol dependence
• Kidney disease, dialysis or a kidney transplant
• Malabsorption conditions (celiac disease, Crohn’s disease, ulcerative colitis)
• Obesity, and pregnancy, especially with preeclampsia or eclampsia
• Rheumatoid arthritis
• Some medicines: antiepileptic drugs (valproic acid, carbamazepine, phenytoin), theophylline and cycloserine, per the NIH fact sheet; Wikipedia also lists isoniazid, penicillamine, hydrocortisone and oral contraceptives
• Eating large amounts of Ginkgo biloba seeds (Wikipedia)
• A systematic review in Parkinson’s disease found low B6 in 30.1% of people on oral levodopa-carbidopa, mostly at levodopa doses of 1000 mg/day or more. The evidence base was small and observational.

Which foods are highest in B6?

The NIH fact sheet lists these amounts, with the Daily Value at 1.7 mg for adults:

Fish, organ meats, potatoes and other starchy vegetables, and non-citrus fruit are the richest sources. About 75% of B6 from a mixed diet is absorbed. The fact sheet says high intakes from food have not been reported to cause adverse effects.

Doses used in studies and official intake levels

These are what researchers used or what agencies publish, not advice for you. The US Recommended Dietary Allowance (RDA) is 1.3 mg/day for adults 19-50, 1.7 mg for men 51+, 1.5 mg for women 51+, 1.9 mg in pregnancy and 2.0 mg while breastfeeding. US adults average about 1.5 mg/day (women) and 2 mg/day (men) from food.

Upper limits: the US limit is 100 mg/day for adults (set by halving the 200 mg/day average used in studies of up to 5 years, because long-term harm data were limited). The European Food Safety Authority in 2023 set 12 mg/day for all adults, including pregnant and breastfeeding women, and 2.2-10.7 mg/day for infants and children. Australia sets a 50 mg/day limit and requires a neuropathy warning label above 10 mg/day, according to Wikipedia. The US limits do not apply to people given B6 as medical treatment under a physician’s care.

Is there a downside? Toxicity symptoms and side effects

Yes. The NIH fact sheet says that 1-6 g of oral pyridoxine a day for 12-40 months can cause severe, progressive sensory neuropathy with ataxia (loss of control of body movements). Severity depends on dose, and symptoms usually stop if the supplement is stopped as soon as nerve symptoms appear. Other effects from excess B6 include painful skin lesions, sun sensitivity, nausea and heartburn.

That case report describes a 73-year-old man with three years of progressive neuropathy. His blood B6 was 259.9 nmol/L (reference 20-125) while taking a multivitamin with 6 mg of B6 for over 10 years, below the European upper limit. One month after stopping it, his dizziness resolved and the numbness improved slightly. It is a single case, and the authors say they cannot rule out other B6 sources. It does show that people differ in sensitivity and that multivitamins, B complexes and energy drinks (up to 40 mg in some) can add up. The systematic review above found that high-dose B6 supplements can cause a mainly sensory neuropathy, though low doses were not proven harmful in people who already have neuropathy.

The NIH fact sheet mentions isolated case reports of birth defects after pyridoxine use in the first half of pregnancy, but a later observational study found none at an average of about 132 mg/day.

Medicine interactions

• Cycloserine (a tuberculosis antibiotic): it increases urinary loss of pyridoxine, which might worsen seizures and neurotoxicity. The fact sheet says pyridoxine supplements can help prevent these effects.
• Antiepileptics (valproic acid, carbamazepine, phenytoin): they speed up B6 breakdown, giving low PLP and high homocysteine. Pyridoxine at 200 mg/day for 12-120 days lowered blood levels of phenytoin and phenobarbital in some research. Whether lower doses matter is unknown.
• Levetiracetam: behavior side effects are the subject of the preliminary B6 research above.
• Theophylline: people on it often have low PLP, which may contribute to its nervous system side effects.
• Levodopa: low B6 was common in observational studies of people with Parkinson’s disease on high doses.

Who should talk to a clinician first?

• Anyone pregnant or breastfeeding, especially for nausea (doses can approach the upper limit)
• Anyone taking antiepileptics, cycloserine, theophylline, levodopa or any medicine regularly; the fact sheet says to discuss B6 status with your health care provider
• People with kidney disease, malabsorption conditions, alcohol dependence or rheumatoid arthritis, who are more likely to have low B6
• Anyone with existing numbness, tingling or neuropathy
• Anyone taking several products that each contain B6
• Parents considering B6 for a child’s seizures, behavior or development

What is still unknown?

• Whether B6 alone, without folic acid and B12, helps with heart disease; most trials combined them.
• Whether long-term low-dose supplements cause neuropathy in some people. The 2023 case report calls for more research.
• Whether B6 improves memory or prevents cognitive decline. The trials were small, short or low quality.
• Why the US limit (100 mg) is more than eight times the European one (12 mg).
• Whether combos such as B6 with magnesium work. Wikipedia reports several trials of high-dose B6 plus magnesium in children with autism found no effect on symptom severity. Nothing in this evidence addresses magnesium lactate with B6 specifically.

How to read a label that lists vitamin B6

• Amount: look for milligrams per serving, and check how many servings per day the label directs. The % Daily Value is based on 1.7 mg, so 100% DV is small, and a 100 mg product is far above it. US food labels list B6 only if it was added.
• Form: pyridoxine hydrochloride is the most common; some products use PLP. The NIH fact sheet says absorption does not differ substantially among supplement forms.
• Proprietary blends: if B6 sits inside a blend with only a combined total, you cannot see how much B6 you get. Ask the maker for the per-ingredient amount.
• Add it up: count B6 from a multivitamin, B complex, stand-alone tablet and fortified drinks or cereals, then compare the total with the upper limits above.
• Claims: wording such as supports nervous system function is not the same as proof of a treatment effect. See our guide on ingredient evidence versus marketing claims.

Before you order or take it

• Which medicines and conditions do you have that could interact with B6?
• How many milligrams of B6 are in everything you already take?
• Does the label show the B6 amount and form without a proprietary blend?
• Have you asked a clinician about a blood B6 test if you suspect a deficiency?

By ClinicalStudyConnect.com Research Desk

This article is for general information purposes only and does not constitute medical advice. Consult your doctor or qualified healthcare provider before making changes to your health routine.