Vitamin B6

What Does Vitamin B6 Do?

• Neurotransmitter synthesis — PLP is an essential cofactor for the enzymes that synthesise serotonin (from tryptophan), dopamine and norepinephrine (from tyrosine), GABA (from glutamate), and histamine. This biochemical role underlies the associations between B6 status and mood, sleep quality, and anxiety. Clinical trials show B6 supplementation reduces PMS symptoms (mood changes, irritability) and reduces anxiety scores in some populations.
• Amino acid metabolism — PLP-dependent enzymes catalyse transamination (transferring amino groups between molecules), decarboxylation (removing carboxyl groups), and racemisation reactions that are central to the synthesis and catabolism of virtually all amino acids. Without adequate B6, protein metabolism is globally impaired.
• Homocysteine regulation and cardiovascular health — along with folate and B12, vitamin B6 is required for the transsulphuration pathway that converts homocysteine to cysteine. Elevated plasma homocysteine is an independent risk factor for cardiovascular disease, stroke, and cognitive decline. B6 deficiency raises homocysteine levels; supplementation in deficient individuals lowers them.
• Haemoglobin synthesis and oxygen transport — PLP is required for delta-aminolevulinic acid (ALA) synthase, the rate-limiting enzyme in haem synthesis. Severe B6 deficiency causes microcytic anaemia (small red blood cells with low haemoglobin), distinct from iron-deficiency anaemia but clinically similar in presentation.
• Immune function — vitamin B6 is required for lymphocyte proliferation, interleukin-2 production, and natural killer cell activity. B6 deficiency impairs both humoral and cell-mediated immunity, and the immune system is particularly sensitive to even marginal deficiency.
• Glycogen metabolism — PLP is required by glycogen phosphorylase, the enzyme that releases glucose from stored glycogen in muscle and liver during fasting or exercise. This makes B6 important for blood glucose regulation and sustained athletic performance.

Signs of Vitamin B6 Deficiency

Vitamin B6 deficiency is uncommon in people with varied diets, but occurs with alcohol use disorder (alcohol impairs B6 absorption and increases degradation), kidney disease, autoimmune conditions (rheumatoid arthritis), and malabsorption disorders. Certain medications — isoniazid (tuberculosis treatment), penicillamine, and cycloserine — inactivate PLP and can induce deficiency. Marginal B6 status (sub-optimal but not clinically deficient) is more common and affects mood, immune function, and homocysteine levels without causing overt symptoms.

• Peripheral neuropathy — numbness, tingling, or burning in the hands and feet; the hallmark of both deficiency and (paradoxically) high-dose supplementation toxicity
• Microcytic anaemia — small, pale red blood cells from impaired haem synthesis; clinically similar to iron-deficiency anaemia
• Seborrhoeic dermatitis — oily, scaly skin rash around the nose, mouth, and eyebrows
• Glossitis — inflamed, swollen, smooth tongue; often with angular stomatitis (cracks at the corners of the mouth)
• Depression, irritability, confusion, and anxiety — from impaired serotonin, dopamine, and GABA synthesis
• Impaired immune function — increased susceptibility to infections due to reduced lymphocyte proliferation
• Elevated homocysteine — increased cardiovascular and cognitive risk, often detected before other symptoms appear
• Seizures in severe deficiency — particularly in infants fed B6-deficient formula; PLP is required for GABA synthesis, the brain's primary inhibitory neurotransmitter

Upper Limit: The Tolerable Upper Intake Level (UL) for vitamin B6 is 100 mg/day for adults from all sources. Chronic supplementation above this level — sometimes used for PMS or carpal tunnel — can cause sensory peripheral neuropathy. Recovery after stopping is typically slow. Dietary B6 from food sources poses no toxicity risk.

How to Get the Most from Vitamin B6

Vitamin B6 from food is well absorbed — approximately 75% bioavailability for a mixed diet. Pyridoxine (common in plant foods) and pyridoxal and pyridoxamine (more common in animal foods) are all absorbed in the jejunum and converted to PLP in the liver, muscle, and brain. Alcohol significantly impairs B6 absorption and accelerates PLP degradation, making alcohol use disorder a major risk factor for deficiency. Unlike some B vitamins, B6 is not significantly stored in the body beyond what is bound to PLP-dependent enzymes, so regular daily intake is important.

Common Vitamin B6 Questions