When Alison Taylor's father lost the ability to walk she had no idea an over-the-counter vitamin was to blame.
Ms Taylor told ABC Radio Melbourne her father was diagnosed with vitamin B6 toxicity — a condition that can cause peripheral neuropathy, or nerve damage — after he was unknowingly consuming about 70 times the recommended daily intake for a man his age.
The 86-year-old was active and living independently until last year when Ms Taylor noticed the strength in his legs declining.
He was eventually admitted to hospital after losing the ability to walk.
"We took him to all sorts of different specialists. He's had a number of consulting neurologists, he's had MRIs, he's had CT scans, everything you could think of to investigate why he was losing his mobility," Ms Taylor said.
After a nine-week stint in hospital, Ms Taylor said one final test was carried out.
"They checked his B6 levels and to quote the doctor, 'they were off the charts'," she said.
Double dosing
Ms Taylor said about four years ago her father went to his GP where routine blood tests revealed he was deficient in B vitamins.
"[The GP] suggested he takes a mega-B supplement, so dad kept taking that," Ms Taylor said.
"In his mega-B there were 50mg [of B6] and in his multivitamin there was also 50mg."
Her father was also taking a magnesium supplement, which contained B6.
"Two of the breakfast cereals that Dad was eating everyday were fortified with B6," she said.
Ms Taylor said it had been difficult watching her father decline.
"Twelve months ago he was driving. He's now in aged care and in a wheelchair," she said.
Her father has been in care for about six weeks to receive additional support and intensive physiotherapy to help rebuild his strength.
Ms Taylor said she was hopeful her father would start to regain his mobility in about six months' time as his B6 levels returned to normal.
"There's no suggestion he'll start to walk as independently as he was before but potentially he won't have to be in the wheelchair," she said.
Condition rare but dangerous
RMIT University nutritional scientist and dietician Jessica Danaher said vitamin B6 toxicity was rare as excess B vitamins were generally flushed out by the body in the form of urine.
"However a toxic level could occur from taking too much B6 from supplements over the long-term," Dr Danaher said.
"In rare cases, having a reduced kidney function as well as taking too much vitamin B6 may contribute to it gradually building up in the body."
Dr Danaher said people generally received enough B6 through a "healthy and varied diet".
"[It's] found in a wide range of foods including meat, poultry, fish, eggs, beans and lentils, seeds and nuts, whole grains, vegetables — especially green and leafy types — and fruits," she said.
Those who consumed high levels of alcohol, had an overactive thyroid, or were taking contraindicated medications could be more likely to develop a deficiency.
"If you are concerned about the levels of nutrients in your blood speak with your GP," Dr Danaher said.
The Therapeutic Goods Association (TGA) said it was aware of reports in Australia and overseas indicating peripheral neuropathy due to high levels of B6 consumption.
In 2020, the TGA said it was reviewing the problem, and has subsequently specified a product containing more than 10mg of B6 must be accompanied by a warning label.
The change came into effect during March 2022 with a 12-month transition process.
The TGA said it would continue to monitor developing evidence and adverse events related to the risk of peripheral neuropathy.
