Vitamin B6: What It Does, Food Sources, and Toxicity Risks

Vitamin B6 is a water-soluble nutrient that serves as a helper molecule in more than 100 chemical reactions throughout the body, making it one of the most broadly active vitamins in human metabolism. Its active form, pyridoxal 5′-phosphate (PLP), is involved in building neurotransmitters, forming hemoglobin, breaking down amino acids, and regulating inflammation. Most people get enough from food without thinking about it, but certain medications, health conditions, and life stages can tip the balance toward deficiency, and taking too much in supplement form carries its own risks.

What B6 Actually Does in the Body

The reason B6 appears in so many health conversations is that its active form, PLP, participates in a remarkably wide range of bodily processes. It is a cofactor for over 100 enzyme-catalyzed reactions, spanning everything from protein metabolism to the creation of red blood cells.¹ Three of its roles stand out as especially important for everyday health.

First, B6 is essential for making neurotransmitters. Your brain needs it to synthesize serotonin, dopamine, noradrenaline, GABA, histamine, and glycine, among others.² When PLP levels drop in the brain, the most obvious result is neurological trouble, with seizures being the most serious manifestation.³

Second, B6 plays a key role in making hemoglobin, the protein in red blood cells that carries oxygen. It is a required coenzyme for the first step in heme production. When B6 is severely depleted, you can develop a type of anemia characterized by abnormally small red blood cells and iron that accumulates in the wrong places inside cells rather than being incorporated into hemoglobin.⁴

Third, B6 helps clear homocysteine from the blood. Homocysteine is a byproduct of protein metabolism, and elevated levels are linked to cardiovascular risk. B6 works alongside folate and B12 to keep homocysteine in check. A Mendelian randomization study found that genetically higher B6 levels were associated with a roughly 12% lower risk of ischemic stroke.⁵

Food Sources and How Much You Actually Absorb

B6 is present in a wide variety of foods. Poultry, fish, potatoes, bananas, chickpeas, fortified cereals, and organ meats are among the richest sources. But how much of the B6 in food your body can use varies quite a bit depending on the source.

Animal products tend to deliver B6 with very high bioavailability, reaching 100% for many foods. Plant sources generally come in lower. Two factors explain most of the gap. Fiber in plant foods reduces bioavailability by about 5 to 10%, a modest effect. The bigger issue is a compound called pyridoxine glucoside, found in many plant foods, which reduces bioavailability by 75 to 80%.⁶ This does not mean plant-based diets are deficient in B6, since many plant foods contain enough total B6 to compensate. But it does mean that if you eat mostly plants, you may need somewhat higher total intake to absorb the same amount.

Cooking affects B6 content in a way that may surprise you. Heat itself does relatively little damage. Research on chickpeas found that B6 is fairly stable against thermal degradation; the bigger loss comes from the vitamin diffusing out of the food into cooking water, particularly during boiling.⁷ Steaming, roasting, or using the cooking liquid (as in soups) preserves more B6 than draining boiled water.

How B6 Gets Recycled Inside You

Your body does not just use B6 once and discard it. Animals, including humans, run a recycling operation called the salvage pathway. When enzymes that depend on B6 are broken down, or when B6 vitamers arrive from digested food, two key enzymes reactivate them so they can be reused. One of these, pyridoxal kinase, adds a phosphate group to pyridoxal. The other, pyridoxine 5′-phosphate oxidase, converts other forms of B6 into PLP, the active version.⁸ This recycling system means your body is fairly efficient at conserving B6 under normal conditions, but it can be overwhelmed by disease, medication use, or genetic variations that disrupt the pathway.

Who Is at Risk for Deficiency

Outright B6 deficiency is uncommon in well-nourished populations, but marginal deficiency is more widespread than most people realize, particularly in older adults, people with kidney disease, and those on certain medications. The causes fall into several distinct categories.⁹

Medications: Some drugs either react directly with PLP, inactivating it, or disrupt the metabolic pathways that recycle B6 vitamers. Isoniazid, a tuberculosis drug, is the classic example. It binds to pyridoxine and forms a compound that gets excreted in urine, draining the body’s supply.¹⁰ Certain antidepressants can also trigger B6 depletion severe enough to cause anemia.¹¹
Kidney dialysis: The dialysis process physically removes B6 vitamers from the blood, increasing losses beyond what normal intake can replace.
Celiac disease: Damage to the intestinal lining impairs the absorption of B6 from food.
Genetic conditions: Some people are born with enzyme defects that either block B6 recycling or cause small molecules to accumulate that react with PLP and inactivate it. These rare conditions can lead to B6-dependent epilepsy in infants.

Symptoms of deficiency tend to show up first in the nervous system and skin. Peripheral neuropathy (numbness or tingling in the hands and feet), confusion, depression, and a cracked, sore tongue are common early signs. Seizures are seen in severe or inborn cases.

B6 for Morning Sickness

One of the most well-established clinical uses for B6 supplementation is treating nausea and vomiting during pregnancy. It is recommended by most obstetric guidelines as a first-line therapy, sometimes alone and sometimes combined with the antihistamine doxylamine.

A systematic review and meta-analysis pooling multiple trials found that supplementation with pyridoxine, whether alone or combined with another active substance, significantly improved nausea scores compared to placebo.¹² Individual trials have compared B6 head-to-head with ginger, another popular remedy. The consistent finding is that both work, and neither clearly outperforms the other. In one trial, both ginger and B6 significantly reduced nausea and vomiting scores after four days, with no meaningful difference between the two groups.¹³ Another trial found both were more effective than placebo, but again could not separate them from each other.¹⁴

The practical upshot: if you’re pregnant and dealing with nausea, B6 is a reasonable and well-supported option. Many clinicians suggest 10 to 25 mg taken three times daily, though you should confirm dosing with your provider. The effect is modest rather than dramatic, and some people respond better than others.

Premenstrual Symptoms

B6 has been studied for premenstrual syndrome (PMS) since at least the 1970s, and the evidence, while not overwhelming, leans positive. A systematic review combining nine trials found that women taking B6 were more than twice as likely to report improvement in overall premenstrual symptoms compared to those on placebo, and the effect was also significant specifically for depressive symptoms.¹⁵ Doses up to 100 mg per day appeared beneficial. Some smaller trials have also tested B6 in combination with calcium or magnesium, finding that the combination reduced both physical and psychological PMS symptoms more than placebo.¹⁶

The caveats are worth noting. Many of the individual trials were small, and the quality of the older studies was mixed. The systematic review’s authors flagged that most trials had methodological limitations. Still, B6 for PMS is one of those cases where the risk at sensible doses is low and the potential benefit is real, so many women and clinicians consider it worth trying. One trial found B6 outperformed both magnesium alone and placebo for overall PMS symptom improvement.¹⁷

Brain Atrophy and Cognitive Decline

As people age, elevated homocysteine levels are associated with faster brain shrinkage and cognitive decline. Because B6, B12, and folate all help metabolize homocysteine, researchers have asked whether supplementing these vitamins can slow the process.

A randomized controlled trial in older adults with mild cognitive impairment tested a daily combination of B6, B12, and folic acid against placebo for two years. The group receiving B vitamins lost brain volume about 30% more slowly than the placebo group. The rate of brain atrophy turned out to be one of the strongest predictors of how fast cognitive test scores declined.¹⁸ The catch is that this was a combined supplement, so it is impossible to attribute the benefit to B6 specifically rather than to B12, folate, or the trio working together. Homocysteine lowering is a team effort among the three vitamins, and most trials test them as a package.

B6 and Inflammation

Low B6 status consistently shows up alongside markers of inflammation, and the relationship appears to go beyond simple coincidence. A study comparing people with coronary artery disease to healthy controls found that those with elevated C-reactive protein (CRP), a key inflammation marker, had substantially lower plasma PLP levels. Critically, this association held even after statistically accounting for homocysteine, suggesting that B6’s relationship to inflammation is at least partially independent of its homocysteine-lowering role.¹⁹

What is less clear is whether low B6 causes inflammation or whether inflammation depletes B6. Inflammatory states increase the body’s consumption of PLP, and at the same time, low PLP may impair the immune system’s ability to regulate itself. The result is likely a feedback loop rather than a simple one-way cause. For the reader, the practical takeaway is that people with chronic inflammatory conditions may have higher B6 requirements and should pay attention to their intake.

Too Much B6 and the Risk of Nerve Damage

Here is where B6 departs from most water-soluble vitamins. The common belief that you can’t really overdose on water-soluble vitamins because you just excrete the excess is dangerously wrong for B6. High-dose supplementation can cause a sensory neuropathy, meaning damage to the nerves that carry sensation from your limbs to your brain. Symptoms include numbness, tingling, loss of coordination, and difficulty walking.

This was first documented clearly in a landmark case series of seven adults who developed severe sensory nerve dysfunction and ataxia (loss of balance and coordination) after taking large daily doses of pyridoxine.²⁰ Since then, numerous additional reports have confirmed the pattern. The damage typically occurs at doses above 200 mg per day taken for extended periods, though there are occasional reports at lower doses in sensitive individuals. Most guidelines set the tolerable upper intake level at 100 mg per day for adults.

The neuropathy from B6 excess can look strikingly similar to the neuropathy from B6 deficiency, which creates a diagnostic trap. Someone with tingling hands and feet might assume they need more B6, when in fact their supplement is the cause. The nerve damage is usually reversible if supplementation is stopped promptly, but prolonged exposure can lead to lasting problems. If you are taking B6 supplements for any reason, stick to the dose your clinician recommended and do not assume that more is better.

The Isoniazid Connection and Other Drug Interactions

The most clinically significant drug interaction with B6 involves isoniazid, used worldwide as a cornerstone of tuberculosis treatment. Isoniazid chemically binds to pyridoxine, forming a compound (a hydrazone) that gets excreted in urine, effectively draining B6 from the body.²¹ Without supplementation, up to half of patients on isoniazid can develop peripheral neuropathy. For this reason, B6 supplementation is routinely co-prescribed with isoniazid, typically at 25 to 50 mg per day.

Other medications that can affect B6 status include certain antiepileptic drugs, the Parkinson’s drug levodopa (which B6 can interfere with when not combined with carbidopa), oral contraceptives, and some antidepressants. The case of the antidepressant amoxapine triggering severe B6 deficiency anemia underscores that these interactions are not just theoretical.²² If you take any medication long-term, it is worth checking whether it has a known B6 interaction.

Your Gut Bacteria Make B6 Too

An emerging area of research involves the gut microbiome’s ability to produce B6 independently of dietary intake. Certain gut bacteria carry the genetic machinery for de novo synthesis of PLP, and recent work suggests this microbial production may have real effects on the host’s nervous system.

In a study using both worm and mouse models, researchers found that colonizing animals with bacteria lacking a key B6 synthesis gene led to lower B6 and dopamine levels, reduced activity of dopamine-producing enzymes, and impaired motor coordination. Supplementing B6 rescued all of these deficits. Intriguingly, analysis of stool samples from people with Parkinson’s disease showed altered abundance of microbial B6 biosynthesis genes compared to healthy controls.²³ This does not prove that gut B6 production drives Parkinson’s disease, and the research is still in early stages. But it raises the interesting possibility that your microbiome’s metabolic output could influence how much active B6 reaches your brain, and that disruptions in gut bacterial communities might contribute to neurological vulnerability.

The Kidney Stone Myth

You may have encountered claims that B6 supplementation helps prevent kidney stones. This idea has circulated in alternative health circles for decades, based on the fact that B6 is involved in oxalate metabolism and most kidney stones contain calcium oxalate. The logic sounds plausible: if B6 helps your body handle oxalate differently, perhaps more B6 means fewer stones.

The data does not support this. A large pooled analysis combining three major prospective cohorts found no association between B6 intake and the risk of developing kidney stones. Comparing the highest intake category to the lowest, the pooled adjusted hazard ratio was 1.03, meaning essentially identical risk.²⁴ Each individual cohort showed the same flat result. If you are taking B6 specifically because someone told you it prevents kidney stones, the evidence suggests you are not getting that benefit.

How B6 Status Is Measured

If you or your doctor want to check your B6 level, the most common test measures plasma PLP concentration. A value below about 20 nmol/L is generally considered deficient, though exact cutoffs vary by lab. But measuring B6 is trickier than measuring most vitamins because several factors can push PLP levels around without reflecting true tissue status. Inflammation lowers circulating PLP even when body stores are adequate. Low albumin levels, abnormal kidney function, and even levels of a bone-related enzyme called alkaline phosphatase can all confound the reading.²⁵

For this reason, researchers have increasingly recommended using a combination of biomarkers rather than relying on PLP alone. Functional biomarkers measure the activity of enzymes that depend on B6, or the levels of metabolites that pile up when B6-dependent reactions slow down. If your plasma PLP comes back borderline low during an acute illness, for example, a functional marker can help distinguish between genuine deficiency and inflammation-driven depletion. In everyday clinical practice, though, most doctors still rely on plasma PLP and interpret it in context, recognizing its imperfections.

The Discovery of a Vitamin

The isolation of B6 has a tidier origin story than many vitamins. In 1934, the Hungarian-born biochemist Paul György identified a previously unknown dietary factor that cured a specific skin disease in rats called acrodynia. He named it vitamin B6 to distinguish it from the other B vitamins already known. Four years later, Samuel Lepkovsky succeeded in isolating and crystallizing the pure compound.²⁶ What neither scientist could have predicted at the time was how many different biological roles this single nutrient would turn out to serve. The 100-plus enzymatic reactions now known to require PLP were uncovered gradually over the following decades, and occasional new roles are still being described. The microbiome research is just one example of how our understanding of this workhorse vitamin continues to expand.