The people unknowingly poisoning themselves with common vitamins

When a 40-year-old gym enthusiast was referred to Professor Matthew Kiernan with rapid, uncontrollable twitches, the Sydney neurologist suspected an autoimmune disease was attacking the man’s nerves.

“This was extreme,” said Kiernan, now chief executive officer and institute director at Neuroscience Research Australia (NeuRA). “This guy came in to see us thinking he might have motor neurone disease, so you can imagine what state he was in.”

The vitamins that come with dosage warnings.

That was until the man mentioned he was interested in bodybuilding and was taking vitamin supplements, some of which contained vitamin B6 (sometimes called pyridoxine).

After research, Kiernan learned that high doses of the vitamin can interrupt or damage nerves outside the brain and spinal cord. Tests revealed the level of B6 in the man’s blood was “through the roof”.

The man’s case, which Kiernan wrote about in the Medical Journal of Australia, is an extreme example of the dangers of over-the-counter supplements taken in large quantities.

Supplements containing B6 or pyridoxine have been associated with more than 1000 adverse events reported to the Therapeutic Goods Administration since 2010. Adverse event notifications are lodged by individuals, and they do not mean the event has been confirmed.

The most common symptoms reported include nausea, hypersensitivity and peripheral neuropathy, in which damage to nerves causes tingling, burning and numbness throughout the body.

“If you take anything about two to three times [more than] what you should be getting, your body’s mechanisms can’t work fast enough to clean them out,” Kiernan said. “The longer the nerves, the more prone they are to toxicity. Generally, people’s legs are longer than their arms, so you lose sensation in your feet and that gradually spreads up your legs and then to your fingers and hands.”

Since 2020, the TGA has required all supplements containing daily doses of more than 50 milligrams of B6 to carry a warning statement. That threshold was lowered to 10 milligrams in 2022 after the agency expressed concerns about a lack of public awareness regarding the dangers of elevated B6 intake.

Kiernan said the lowering of the threshold was a step in the right direction, but that it would take more than a warning label to increase community awareness.

“If the guy in my case report knew that he was poisoning himself, he wouldn’t have taken it,” he said. “They might think they’ve got this funny symptom because they’ve got a condition or disease, but unless they put two and two together, they don’t realise, ‘Oh this thing I’m eating is poisoning me’.”

Gillian Clarke is still active in her Port Macquarie community despite struggling with the symptoms of long-term peripheral neuropathy.

Kiernan told the man to stop taking the supplement, and the twitches gradually receded. All the skin peeled off his feet – another symptom of pyridoxine toxicity – but he avoided long-term damage to his nerves.

For others, the damage can be long-lasting.

Gillian Clarke, from Port Macquarie on the Mid-North Coast, started taking magnesium supplements after her badminton games to prevent cramps at night.

She started losing feeling in her feet around 2012, and was diagnosed with peripheral neuropathy. But neither her GP nor her neurologist could find the cause, and the symptoms gradually worsened.

“Ten years ago I was a fit old lady, ex-badminton and tennis competition player, still striding around quite confidently and enjoying overseas holidays with friends,” she said. “Now I lurch around looking more like an old penguin who has had two glasses of sherry!”

It wasn’t until the 86-year-old joined a social media support group that she realised the two magnesium tablets she had been taking every day for more than 20 years contained vitamin B6 at levels 80 times the recommended dose for her age group.

Clarke said the warning statement, written in small print on the back of her vitamins, was easy to miss. She wants the TGA to find a better way to warn doctors, pharmacists and patients about the risks of taking supplements containing B6.

“Some medical professionals in parts of Australia are aware of the connection between B6 toxicity and peripheral neuropathy and are looking out for this but, very sadly for me, none of the people I have consulted were aware of it,” she said. “People are unknowingly poisoning themselves.”

A spokesman for the TGA said the agency continued to monitor the safety of supplements containing B6 and “will take further regulatory action if necessary”.

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