Vitamin B6
Vitamin B6 (Pyridoxine/P5P) Supplement Fact Sheet
1. Introduction
Vitamin B6, a group of water-soluble compounds, is an essential micronutrient vital for numerous metabolic processes in the human body. The term Vitamin B6 encompasses six forms: pyridoxine (PN), pyridoxal (PL), pyridoxamine (PM), and their respective 5′-phosphate esters (PNP, PLP, and PMP).
The most biologically active and crucial form is Pyridoxal 5′-Phosphate (P5P or PLP). P5P serves as a coenzyme for over 100 enzymes, primarily in the metabolism of amino acids, but also in carbohydrate and lipid metabolism. It is essential for the synthesis of neurotransmitters, hemoglobin, and the regulation of homocysteine levels [1].
Mechanism of Action
P5P functions as a coenzyme in transamination, decarboxylation, racemization, and elimination reactions involving amino acids. Key mechanisms include:
- Neurotransmitter Synthesis: P5P is a required cofactor for the synthesis of major neurotransmitters, including serotonin, dopamine, GABA, and norepinephrine, from their precursor amino acids.
- Homocysteine Metabolism: P5P is a coenzyme for cystathionine β-synthase and cystathionine γ-lyase, two enzymes that convert the potentially harmful amino acid homocysteine into cysteine, thereby lowering plasma homocysteine levels.
- Gluconeogenesis: It plays a role in the breakdown of glycogen (glycogenolysis) and the synthesis of glucose from non-carbohydrate sources (gluconeogenesis).
2. Chemical Composition/Key Bioactive Roles
The Vitamin B6 family comprises several vitamers, all of which are converted into the active coenzyme form, P5P.
| Compound | Chemical Form | Key Bioactive Role |
|---|---|---|
| Pyridoxal 5′-Phosphate (P5P) | Active Coenzyme | Cofactor for >100 enzymes; essential for amino acid, carbohydrate, and lipid metabolism; neurotransmitter synthesis. |
| Pyridoxine (PN) | Supplement form | Primary form used in fortified foods and supplements; converted to P5P in the liver. |
| Pyridoxal (PL) | Natural form | Found in food sources; converted to P5P. |
| Pyridoxamine (PM) | Natural form | Found in food sources; converted to P5P. |
3. Health Benefits
Vitamin B6 supplementation is associated with several health benefits, particularly in populations with deficiency or specific health conditions.
Homocysteine Reduction and Cardiovascular Health
Vitamin B6, along with B12 and folate, is crucial for regulating blood levels of homocysteine. Elevated homocysteine is an independent risk factor for cardiovascular disease and stroke. Clinical studies have demonstrated that B vitamin supplementation effectively reduces plasma homocysteine concentrations [2, 3]. While B6 alone may not always show a significant effect on reducing cardiovascular events, its role as a cofactor in the homocysteine metabolic pathway is well-established.
Premenstrual Syndrome (PMS) Symptom Relief
A systematic review and meta-analysis of randomized controlled trials suggest that Vitamin B6 supplementation can be a beneficial and effective treatment for premenstrual symptoms, including mood swings, irritability, and breast tenderness. Doses up to 100 mg/day have been shown to be effective in treating premenstrual symptoms and premenstrual depression [4].
Neurological and Cognitive Function
Due to its critical role in neurotransmitter synthesis, Vitamin B6 is essential for normal brain development and function. Deficiency in P5P can lead to neurological issues, including seizures and neuronal hyperexcitability. Supplementation is sometimes used in the management of specific, rare forms of epilepsy (e.g., pyridoxine-dependent epilepsy) and is being investigated for its potential role in reducing the risk of cognitive decline by lowering homocysteine levels [1, 5].
4. Dosage and Usage
Recommended Dietary Allowance (RDA)
The Recommended Dietary Allowance (RDA) for adults (19-50 years) is 1.3 mg/day. For adults over 50, the RDA is 1.7 mg/day for men and 1.5 mg/day for women [6].
Supplementation Dosages
Therapeutic and supplemental dosages vary widely based on the intended use:
- General Deficiency: Doses of 10–20 mg/day are common in multivitamin formulations.
- PMS Relief: Clinical studies often use doses up to 50–100 mg/day [4].
- High-Dose Therapy: In specific clinical settings, such as for managing high homocysteine or certain neurological conditions, doses may reach 200–500 mg/day, but this should be under medical supervision [7].
Food Sources
Vitamin B6 is widely available in foods. Rich sources include:
- Chickpeas (garbanzo beans)
- Beef liver
- Tuna and Salmon
- Potatoes and other starchy vegetables
- Fortified cereals
5. Safety and Precautions
Safety and Tolerable Upper Intake Level (UL)
Vitamin B6 is generally safe when taken in recommended doses. The Tolerable Upper Intake Level (UL) for adults is 100 mg/day [6]. This is the maximum daily intake unlikely to cause adverse health effects.
Side Effects and Toxicity (Serious Warning)
Serious Warning: Chronic intake of high-dose Vitamin B6 (typically exceeding the UL for a prolonged period) can lead to sensory neuropathy. Symptoms of toxicity include:
- Severe and progressive sensory neuropathy (nerve damage)
- Ataxia (loss of control of bodily movements)
- Dermatological lesions
- Gastrointestinal symptoms (nausea, heartburn)
Neuropathy is generally associated with doses of 1,000 mg/day or more taken over a long period, but some cases have been reported at lower doses, particularly between 100 mg and 500 mg/day [7].
Contraindications and Drug Interactions
- Contraindications: Individuals with a history of sensitivity to pyridoxine should avoid supplementation.
- Drug Interactions: Vitamin B6 can interact with several medications, potentially altering their effectiveness:
- Levodopa (L-DOPA): High doses of pyridoxine can decrease the effectiveness of Levodopa, a drug used to treat Parkinson’s disease, by increasing its peripheral metabolism. This interaction is less common with modern Levodopa/carbidopa combinations.
- Phenytoin (Dilantin) and Phenobarbital: Pyridoxine may decrease the serum concentrations of these anti-seizure medications.
- Isoniazid, Hydralazine, Penicillamine: These drugs can form complexes with P5P, leading to functional Vitamin B6 deficiency, which may necessitate supplementation [8].
6. References
[1] Office of Dietary Supplements (ODS), National Institutes of Health. Vitamin B6 Fact Sheet for Health Professionals. Available at: https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/[2] Olaso-Gonzalez, G., et al. (2022). Impact of supplementation with vitamins B6, B12, and/or folic acid on the reduction of homocysteine levels in patients with mild cognitive impairment: A systematic review and meta-analysis. IUBMB Life, 74(7), 642–653. Available at: https://pubmed.ncbi.nlm.nih.gov/34058062/[3] Kataria, N., et al. (2021). Effect of Vitamin B6, B9, and B12 Supplementation on Homocysteine Levels in Stroke Patients: A Systematic Review and Meta-Analysis. Cureus, 13(6), e15664. Available at: https://pubmed.ncbi.nlm.nih.gov/34123655/[4] Wyatt, K. M., et al. (1999). Efficacy of vitamin B-6 in the treatment of premenstrual syndrome: systematic review. BMJ, 318(7195), 1375–1381. Available at: https://pubmed.ncbi.nlm.nih.gov/10334745/[5] Girgis, V., et al. (2025). Moderate pyridoxal phosphate deficiency enhances neuronal hyperexcitability and anxiety-like behavior in adult mice. Frontiers in Neuroscience, 19. Available at: https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2025.1621349/full[6] Mayo Clinic. Vitamin B-6. Available at: https://www.mayoclinic.org/drugs-supplements-vitamin-b6/art-20363468[7] Hemminger, A., et al. (2023). Vitamin B6 Toxicity. StatPearls Publishing. Available at: https://www.ncbi.nlm.nih.gov/books/NBK554500/[8] Drugs.com. Vitamin B6 (Pyridoxine) Interactions Checker. Available at: https://www.drugs.com/drug-interactions/pyridoxine,vitamin-b6.htmlCategory: Vitamin
