Vitamin B6 (pyridoxine): high-dose supplements and nerve damage

Pyridoxine and its related forms act as helpers in many enzyme reactions. The NHS says B6 helps the body use and store energy from protein and carbohydrate and helps form haemoglobin in red blood cells. MedlinePlus adds roles in making antibodies, supporting nerve function and regulating blood glucose.

Good food sources include pork, poultry, fish, peanuts, soya beans, wheatgerm, oats, bananas, milk and fortified cereals, so a mixed diet makes deficiency unlikely.

Being water-soluble does not make a vitamin harmless in large amounts. At high intakes, pyridoxine can injure the long sensory nerves, producing tingling, numbness, burning or pain that starts in the feet and hands. A systematic review of the literature describes a pure sensory, length-dependent axonal neuropathy as the typical pattern.

Case reports and studies cited in the review involve daily amounts of 200mg and above, with some patients taking grams a day. The review also records that people on 200mg had a higher neuropathy risk than those on 150mg, and that symptoms appeared within weeks to months in some of them.

The NHS advice is conservative: do not take more than 10mg a day in supplements unless advised by a doctor. It explains that 200mg or more a day can lead to peripheral neuropathy, and that evidence for the range between 10mg and 200mg is unclear, meaning no one can state how long those doses may be taken safely.

Many shop-bought B-complex, energy, hair-skin-nails and “mood” products contain more than 10mg per tablet. It is worth reading the label for pyridoxine, pyridoxine hydrochloride or pyridoxal 5’-phosphate, and adding up all products, because people sometimes combine a multivitamin, a B-complex and a magnesium-B6 tablet without realising.

• Check the milligrams of B6 on every supplement you use.

• Add them together if you take more than one product.

• Do not take high-dose B6 for premenstrual symptoms or morale without discussing it with a pharmacist or GP.

• A prescribed course of B6 is different and should follow the prescriber’s instructions and review plan.

Symptoms are usually symmetrical, starting in the toes and fingers, and may include numbness, pins and needles, a burning feel, poor balance in the dark and clumsiness with buttons or keys. Sudden weakness, difficulty walking, or involvement of the face or breathing is not typical of B6 and needs urgent assessment.

See a GP promptly if you have these symptoms and take B6. The clinician will review your supplements, medicines and alcohol use, and check for other common causes such as diabetes, low vitamin B12, thyroid problems and kidney disease. Blood tests, including B6 and B12 levels, and sometimes nerve conduction studies may be arranged.

Stopping the supplement is the main treatment. In the systematic review, patients generally reported improvement after discontinuation, though in an older series none had signs or symptoms that completely resolved. Recovery can be slow and may be partial, which is the best argument for not delaying a stop once symptoms appear.

B6 interacts with a few prescribed drugs, including some used for epilepsy, so anyone on regular medicines should ask a pharmacist before adding it. B6 also appears in some pregnancy-sickness products, and any such use should be agreed with a midwife or doctor rather than self-selected.