12/09/2017 9:17 AM AEST | Updated 12/09/2017 9:27 AM AEST

Melbourne Man Has Cyanide Poisoning After Self-Medicating With Apricot Kernels

But he still won't give up the daily ritual.

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The man had been ingesting large quantities of apricot kernels, in the belief they could help prevent cancer.

Supplements, vitamins and other complementary medicines are a $3.5 billion industry in Australia, but one Melbourne man has highlighted the potentially life-threatening consequences of taking health fads and so-called "miracle diets" too far.

When the 67-year-old went into hospital for routine surgery, doctors were at a loss to figure out why the seemingly fit and healthy pensioner who didn't smoke had low levels of oxygen in his red blood cells -- something usually associated with serious illnesses like lung disease, anaemia and heart disease.

"This gentleman had told me he cycles 80 kilometres a week," the patient's anaesthetist, Dr Alex Konstantatos from Alfred Hospital, told HuffPost Australia.

Chatting to the man, who was in remission from prostate cancer, Konstantatos uncovered that he had been self-medicating with apricot kernels.

"The gentleman involved has a scientific background and he had read that apricot kernel extract would prevent his cancer from recurring," Dr Konstantatos explained.

Early in 2016, apricot kernels rose to prominence as the latest "superfood" -- touted as bursting with nutrients and cancer-fighting agents. But such claims have since been debunked, with medical experts warning of the seed's high levels of amygdalin, a substance which the human body converts into the toxic chemical, cyanide.

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Almonds also contain cyanide, but in much lower quantities.

Eating more than two kernels a day puts an adult over the safe level of cyanide -- a toxic chemical that can lead to dizziness, breathing difficulties, joint and muscle pains and, ultimately, death, according to Australia's food safety watchdog.

The 67-year-old had been taking three tablets of the apricot kernel-based supplement Novodalin each day, as well as grinding up his own brew at home -- adding up to more than 17mg of cyanide a day.

Blood tests revealed he had cyanide in his bloodstream at 25 times acceptable levels.

Yet despite stern warnings from the medical team at Alfred Hospital and clear evidence that his body wasn't carrying oxygen as it should, he refused to give up his daily ritual.

The effects of dosing yourself with substantial but non-lethal quantities of cyanide every day have never been tested, Konstantatos said.

"What we do know is that a big enough dose can kill you."

In fact, cyanide is so lethal and its effects so unknown, there is no standard test for it in those who are alive. To conduct this man's blood test, his blood samples had to be transported to Sydney and tested by a forensics team.

"If you're taking something which releases cyanide in a way where you're not actually measuring how much you take, there's a very small difference between what might be a small dose of cyanide and that which would seriously effect parts of your body, like your brain and heart," Konstantatos warned.

The 67-year-old was taking three Novodalin supplements every day, as well as his own home brew. Novodalin markets itself as a remarkable and suberb quality B17 supplement , but health experts warn the so-called vitamin is highly toxic in sufficient quantities.

There is also no evidence indicating that the extract cures cancer.

"(Cyanide) can stop basically all cells in the body from incorporating oxygen and turning that oxygen into energy so that the cell can function.

"If you compare that to an anti-cancer drug that has been scientifically validated, a lot of (them) will kill cells but they will selectively kill cells. There's been a lot of research conducted to show that those chemotherapy agents will predominantly kill the cancer cells and do as little harm as possible."

In 2015, Food Standards Australia and New Zealand banned the sale of apricot kernels in foodstuffs, but the supplement, often marketed as B17, is still available online via alternative health food websites -- many of which advocate consuming up to 20 kernels per day.

With around two thirds of Aussies saying they've taken some form of complementary medicine in the past year, Konstantatos has voiced concern about the rising prominence of alternative medicines which haven't been scientifically validated.

He hopes this case will send a warning about the dangers of self-prescribing such medicines, and will encourage doctors to ask patients about what complementary medicines they take.

"People should research every medication that they choose to take that is not prescribed to them and educate themselves about the potential effects," he said.

The findings of the tests on this patient were published in international peer-reviewed journal BMJ Case Reports on Tuesday.