Poison fruit: toxic apricot kernels are no cure for cancer

The highly dangerous appeal of eating apricot kernels as a form of self-medication are graphically illustrated by the story of an Australian man detailed in the British Medical Journal.

The unnamed man from the state of Victoria receives the dubious honour of being written up as a case report, describing the urgent intervention of hospital staff to save him from chronic cyanide poisoning.

Written by four doctors from the Alfred Hospital in Melbourne, the case study describes a “seemingly well 67-year-old man” who, while under anaesthetic for a 15-minute routine procedure, suddenly experienced a potential fatal drop in oxygen levels (a condition known as hypoxia).

After being stabilised, medical staff conducted a battery of tests to track down the cause of the oxygen drop. X-rays revealed nothing unusual, and lung function was fine. There was no indication of cardiac irregularities, and blood work came back normal.

One particular assay, however, revealed the problem: high levels of cyanide in his blood. Tests found 1.6 milligrams of cyanide per litre. This corresponds to “moderate” cyanide poisoning, but the dividing lines are thin: a level of just 2.5 milligrams per litre is enough to induce coma and death.

In interview, the patient revealed that he had consumed apricot kernels every day for the past five years. His self-medication routine involved three tablets of commercially manufactured kernel product and two teaspoons of a homemade preparation.

After testing, the commercial product was found to contain 220 miligrams of cyanide per kilogram, and the homemade substance contained 1600 milligrams per kilo.

Overall, the man was consuming 17 milligrams of cynanide each day. The European Food Safety Authority recommends no more than one-third of a gram as the maximum safe dose for adults (and just 0.06 grams for children).

Apricot kernels are sold and marketed by a large number of “natural health” advocates. Rules restricting the promotion of unproven health claims for non-medical products in many countries mean that kernel products are often sold simply as general tonics to aid health and digestion.

However, in less public literature, they are touted as cures for many conditions, particularly cancer. Kernel preparations aimed at cancer sufferers are sometimes marketed as laetrile or amygdalin.

Meta-analyses into kernel cancer-curing claims have all reported that few if any purported studies meet basic research standards.

Typical is a Cochrane meta-analysis published in 2015 and led by Stefania Milazzo of the Paracelsus Medical University in Germany.

With colleague Marcus Horneber, Milazzo searched eight medical databases and two registers, finding 200 references to kernel treatment for cancer. The pair found no studies that met the criteria for a randomised clinical trial.

The conclusions were stark: “There is a considerable risk of serious adverse effects from cyanide poisoning after laetrile or amygdalin, especially after oral ingestion,” the researchers wrote. “The risk–benefit balance of laetrile or amygdalin as a treatment for cancer is therefore unambiguously negative.”

In the latest case, the Melbourne doctors, led by Alex Konstantatos, echo those sentiments.

“Physicians should be aware that self-prescription with complementary medicines can result in potentially harmful toxicities, and may be more common that currently understood,” they conclude.

The patient’s cyanide levels, by the way, dropped to safe levels after three days off his self-meds. However, despite his doctors making their concerns plain, he chose to resume taking them after he was discharged from hospital.