Nial Wheate, Macquarie University and Slade Matthews, University of Sydney

Side effects from taking too much vitamin B6 – including nerve damage – may be more widespread than we think, Australia’s medicines regulator says.

In an ABC report earlier this week, a spokesperson for the Therapeutic Goods Administration (TGA) says it may have underestimated the extent of the side effects from vitamin B6 supplements.

However, there are proposals to limit sales of high-dose versions due to safety concerns.

A pathologist who runs a clinic that tests vitamin B6 in blood samples from across Australia also appeared on the program. He told the ABC that data from May suggests 4.5% of samples tested had returned results “very likely” indicating nerve damage.

So how can vitamin B6 be toxic?

Vitamin B6, also known as pyridoxine, plays an important role in keeping the body healthy. It is involved in the metabolism of proteins, carbohydrates and fats in food. It is also important for the production of neurotransmitters – chemical messengers in the brain that maintain its function and regulate your mood.

Vitamin B6 also supports the immune system by helping to make antibodies, which fight off infections. And it is needed to produce haemoglobin, the protein in red blood cells that carries oxygen around the body.

Some women take a vitamin B6 supplement when pregnant. It is thought this helps reduce the nausea associated with the early stages of pregnancy. Some women also take it to help with premenstrual syndrome.

However, most people don’t need, and won’t benefit from, a vitamin B6 supplement. That’s because they get enough vitamin B6 from their diet through meat, breakfast cereal, fruit and vegetables.

You don’t need much. A dose of 1.3–1.7 milligrams a day is enough for most adults.

Currently, vitamin B6 supplements with a daily dose of 5–200mg can be sold over the counter at health food stores, supermarkets and pharmacies.

Because of safety concerns, the TGA is proposing limiting their sale to pharmacies, and only after consultation with a pharmacist.

Daily doses higher than 200mg already need a doctor’s prescription. So under the proposal that would stay the same.

What happens if someone takes too much?

If someone takes too much vitamin B6, in most cases the excess will be excreted in their urine and most people won’t experience side effects. But there is a growing concern about long-time, high-dose use.

A side effect the medical community is worried about is peripheral neuropathy – where there is damage to the nerves outside the brain and spinal cord. This results in pain, numbness or weakness, usually in hands and feet. We don’t yet know exactly how this happens.

In most reported cases, these symptoms disappear once the person stops taking the supplement. But for some people it may take three months to two years before they feel completely better.

There is growing, but sometimes contradictory, evidence that high doses (more than 50mg a day) for extended periods can result in serious side effects.

A study from the 1990s followed 70 patients for five years who took a dose of 100 to 150mg a day. There were no reported cases of neuropathy.

But more recent studies show high rates of side effects.

A 2023 case report provides details of a man who was taking multiple supplements. This resulted in a daily combined 95mg dose of vitamin B6, and he experienced neuropathy.

Another report describes seven cases of neuropathy linked to drinking energy drinks containing vitamin B6.

Reports to the TGA’s database of adverse events notifications (a record of reported side effects) shows 174 cases of neuropathy linked with vitamin B6 use since 2023.

What to do if someone takes too much vitamin B6?

The current advice is that someone who takes a dose of 50mg a day or more, for more than six months, should be monitored by a health-care professional.

There are three side effects to watch out for, the first two related to neuropathy:

1. numbness or pain in the feet and hands
2. difficulty with balance and coordination as a result of muscle weakness
3. heartburn and nausea.

People with worrying side effects after taking vitamin B6 supplements can contact their state’s poison information centre on 13 11 26 for advice.

Nial Wheate, Professor, School of Natural Sciences, Macquarie University and Slade Matthews, Senior Lecturer, Toxicology, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.