In recent weeks, reports have been circulating about severe reactions in people who've taken over-the-counter vitamin B6 supplements.

Vitamin B6 poisoning can injure nerves and lead to symptoms including numbness, tingling and even trouble walking and moving.

In some cases, those affected didn’t know the product contained any vitamin B6.

So what is vitamin B6, where is it found and how much is too much? Here's what you need to know about this essential nutrient.

What is vitamin B6?

Vitamin B6 (also known as pyridoxine) is a group of six compounds that share a similar chemical structure.

It is an essential nutrient, meaning we need it for normal body functions, but we can't produce it ourselves.

Adults aged 19-50 need 1.3mg of vitamin B6 per day. The recommended dose is lower for teens and children, and higher for those aged 51 and over (1.7mg for men and 1.5mg for women) and women who are breastfeeding or pregnant (1.9mg).

Most of us get this is our diet – largely from animal products, including meat, dairy and eggs.

The vitamin is also available in a range of different plant foods, including spinach, kale, bananas and potatoes, so deficiency is rare, even for vegetarians and vegans.

The vitamin B6 we consume in the diet is inactive, meaning the body can't use it. To activate B6, the liver transforms it into a compound called pyridoxal-5′-phosphate (PLP).

In this form, vitamin B6 helps the body with more than 140 cellular functions, including building and breaking down proteins, producing red blood cells, regulating blood sugar and supporting brain function.

Vitamin B6 is important for overall health and has also been associated with reduced cancer risk and inflammation.

Despite being readily available in the diet, vitamin B6 is also widely included in various supplements, multivitamins and other products, such as Berocca and energy drinks.

Should we be worried about toxicity?

Vitamin B6 toxicity is extremely rare. It almost never occurs from dietary intake alone, unless there is a genetic disorders or disease that stops nutrient absorption (such as coeliac disease).

This is because all eight vitamins in the B group are water-soluble. If you consume more of the vitamin than your body needs, it can be excreted readily and harmlessly in your urine.

However, in some rare cases, excessive vitamin B6 accumulates in the blood, resulting in a condition called peripheral neuropathy. We're still not sure why this occurs in some people but not others.

Peripheral neuropathy occurs when the sensory nerves – those outside our brain and spinal cord that send information to the central nervous system – are damaged and unable to function. This can be caused by a wide range of diseases (and is most well known in type 2 diabetes).

The most common symptoms are numbness and tingling, though in some cases patients may experience difficulty with balance or walking.

We don't know exactly how excess vitamin B6 causes peripheral neuropathy, but it is thought to interfere with how the neurotransmitter GABA sends signals to the sensory nerves.

Vitamin B6 can cause permanent damage to nerves. Studies have shown symptoms improved when the person stopped taking the supplement, although they didn't completely resolve.

What is considered excessive? And has this changed?

Toxicity usually occurs only when people take supplements with high doses of B6.

Until 2022, only products with more than 50mg of vitamin B6 were required to display a warning about peripheral neuropathy. But the Therapeutic Goods Administration lowered this and now requires any product containing more than 10mg of vitamin B6 to carry a warning.

The Therapeutic Goods Administration has also halved the daily upper limit of vitamin B6 a product can provide – from 200mg to 100mg.

These changes followed a review by the administration, after receiving 32 reports of peripheral neuropathy in people taking supplements. Two thirds of these people were taking less than 50mg of vitamin B6.

The Therapeutic Goods Administration acknowledges the risk varies between individuals and a lot is unknown. Its review could not identify a minimum dose, duration of use or patient risk factors.

But I thought B vitamins were good for me?

Too much of anything can cause problems.

The updated guidelines are likely to significantly lower the risk of toxicity. They also make consumers more aware of which products contain B6, and the risks.

The Therapeutic Goods Administration will continue to monitor evidence and revise guidelines if necessary.

While vitamin B6 toxicity remains very rare, there are still many questions about why some people get peripheral neuropathy with lower dose supplements.

It could be that some specific vitamin B compounds have a stronger effect, or some people may have genetic vulnerabilities or diseases which put them at higher risk.

So what should I do?

Most people don't need to actively seek vitamin B6 in supplements.

However, many reports to the Therapeutic Goods Administration were of vitamin B6 being added to supplements labelled as magnesium or zinc – and some weren't aware they were consuming it.

It is important to always check the label if you are taking a new medicine or supplement, especially if it hasn't been explicitly prescribed by a health-care professional.

Be particularly cautious if you are taking multiple supplements. While one multivitamin is unlikely to cause an issue, adding a magnesium supplement for cramping, or a zinc supplement for cold and flu symptoms, may cause an excessive vitamin B6 dose over time, and increase your risk.

Importantly, pay attention to symptoms that may indicate peripheral neuropathy, such as pins and needles, numbness, or pain in the feet or hands, if you do change or add a supplement.

Most importantly, if you need advice, you should talk to your doctor, dietitian or pharmacist.