Over the last few years, many people have read or heard that apricots contain an anticancer compound called amygdalin (aka laetrile or “B17”), and some have used it in efforts to help prevent or treat cancer.
The main question we need to ask is this:
1. Are there circumstances where eating small amounts of laetrile (“B17”) could be safe and could it have any benefit with regards to cancer?
Theories on How it Works
After laetrile enters the body it is broken down into hydrogen cyanide, prunasin and benzaldehyde, which are thought to possess anticancer activity.
Results of In Vitro (Test Tube) Studies
There are five test tube studies that have been done on cancer cells. Most of these studies showed that amygdalin inhibited growth of cancer cells. However, one study compared amygdalin against both regular human cells and cancerous cells and showed that amygdalin inhibited growth of both cells by the same amount and did not selectively target cancer cells. Studies are listed at the end of this post.
Nonetheless, it is unlikely to find a doctor who makes recommendations based on In Vitro (test tube research) studies because over the years scientists and practitioners have come to the realization that what happens inside of a test tube rarely happens the same way in a person. Most compounds that have demonstrated anticancer effects in a test tube do not demonstrate any anticancer activity when tested in human clinical trials, or even in animal trials. This is due to the complexity of human physiology and cancer itself, as well as differences in dosing.
Results of Animal Studies
There are seven main animal studies that have been completed. Amygdalin alone did not demonstrate cancer activity in 6 out of the 7 studies. The last study demonstrated a modest decline in tumor growth when amygdalin was injected into the abdomen at 300mg per kilogram of body weight. Given each apricot kernel has around 26mg of amygdalin[1], the equivalent dose in a human might be around 700 apricot kernels. A dose of 30 kernels was reported in one case-report to be sufficient to risk a coma. If you are still considering consuming them, Health Canada recommends consuming no more than 3 kernels per day[2]
Results of Human Studies
There are only two published human studies available, and neither of them compared amygdalin use to no amygdalin use, so it is difficult to determine whether the results were due to the amygdalin or other treatments the patients were undergoing. The first trial was primarily used to assess the optimum dosage; however during the study two patients who were eating raw apricot kernels developed symptoms of cyanide poisoning.[3]
The second trial was conducted on 175 patients and used to assess efficacy.[4] They found:
● Only one patient demonstrated an anticancer response
● 54% of patients had measurable disease progression at the end of the intravenous course of treatment
● All patients had disease progression 7 months after completing intravenous therapy
● When apricot kernels were given orally this led to cyanide levels in the blood approaching the lethal range, with several patients developing symptoms of cyanide toxicity
● No substantive benefit observed in cure, improvement or stabilization of cancer, improvement of symptoms related to cancer, or extension of lifespan
● Patients exposed to this agent should be instructed about the danger of cyanide poisoning, and their blood cyanide levels should be carefully monitored. Amygdalin (Laetrile) is a toxic drug that is not effective as a cancer treatment.
Risks and Cautions
Cyanide poisoning has been documented in a number of cases with ingestion of apricot kernels. One report mentioned that 20 minutes after ingestion of 30 apricot kernels a 41 year old female became weak and experienced numbness. She then progressed towards coma, with weakness and difficulty breathing.[5] She was found in time by paramedics and treated with antidotal therapy. Another report found cyanide intoxication after consumption of 70 apricot kernels in a 58 year old man.[6]
Cyanide poisoning has been shown to cause symptoms such as:
Abdominal pain, nausea, vomiting, diarrhea, dizziness, headache, hives, rash, itchy or swollen skin, cyanosis, light-headedness, confusion, weakness, drowsiness, palpitations, hyperpnea, seizures, liver damage, hypotension, and trembling. Late symptoms include respiratory failure, paralysis, coma, and death (4,31757,65124,94064,94065). There have been multiple cases reported of severe acute cyanide poisoning, some resulting in fatalities, after the consumption of apricot kernels by children and adults.[7]
Another important note is that cyanide poisoning occurs more frequently when laetrile is taken orally [21-23]. This appears to be due to bacteria and plant enzymes (beta-glucosidases) that activate the release of cyanide after laetrile has been ingested.[17,22].
Recommendations from Major Organizations
1. Laetrile has shown little anti-cancer activity in animal studies
2. Laetrile has shown no anti-cancer activity in human studies
3. Side effects associated with laetrile toxicity mirror those of cyanide poisoning (laetrile is converted into cyanide by bacteria and enzymes in the gut)
a. Which include liver damage, fever, coma, death
4. Laetrile is not approved for use in the USA
CochraneSystematicReviews, 2015 states:
1. Claims that laetrile have benefit are not supported by sound clinical data
2. There is a considerable risk of serious adverse effects from cyanide poisoning, especially after oral ingestion
3. The risk-benefit balance of laetrile or amygdalin as a treatment for cancer is therefore unambiguously negative.
Memorial Sloan Kettering states:
When fed to laboratory animals that had cancer cells implanted in them, amygdalin did not reduce the tumor size or slow their growth. In a clinical study, cancer patients using amygdalin did not have any benefits, but some showed cyanide toxicity. Cancer patients should not use this product in the current form until more is known about its safety and effectiveness.
Conclusion
All major cancer organizations currently recommend avoiding both supplement and food sources of amygdalin, given the poor history of efficacy and high potential for toxicity from amygdalin. There are many other natural therapies that are backed with human studies and have demonstrated good safety and are associated with reduced cancer recurrence and improved prognosis. At our clinic, Dr. Baker (ND) prioritizes these options above less-proven therapies that have substantial risks associated with them.
Test Tube (In Vitro) Studies
[15]
A 50% inhibition of growth by both normal human cells and cancerous cells observed by amygdalin at a concentration of 3.5 mg/mL. No selective killing of leukemia cell lines compared to normal bone marrow cells
[16]
In Vitro (test tube) study on human colon cancer cells
Modest (10%–30%) cytotoxicity seen with amygdalin concentrations of 0.5–5.0 mg/mL
[17]
[18]
In Vitro (test tube) study Hepatoma cells
Dose required to inhibit growth of cancer cells by 50% was 458.10 mg/mL with amygdalin
[19]
Modest (10%–50%) cytotoxicity seen with amygdalin concentrations of 5–20 mg/mL
Animal Studies
[2]
Rodent tumors (L1210 lymphoid leukemia, P388 lymphocytic leukemia, B16 melanoma, and Walker 256 carcinosarcoma)
No antitumor activity of amygdalin alone (25–3,200 mg/kg); potentiation of toxicity of amygdalin when combined with beta glucosidase
[3]
Three transplantable rodent tumors (osteogenic sarcoma, Lewis lung carcinoma, and P388 leukemia)
No antitumor activity at 20% of lethal dose (LD20)
[4]
DMBA-induced rat mammary carcinoma and the following transplanted experimental tumors: sarcoma 180, plasma cell tumor LPC-1, leukemia L1210, Mecca lymphosarcoma, Ridgway osteogenic sarcoma, sarcoma T241, mammary carcinoma E0771, Taper liver tumor, Ehrlich carcinoma (solid and ascites), and Walker carcinosarcoma 256
Not effective at treating, preventing, or delaying development of tumors
[6]
B16 melanoma and BW5147 AKR leukemia
Ineffective
[9]
Murine mammary adenocarcinoma
No effect of amygdalin alone. Enhanced antitumor activity of combination of oral vitamin A, amygdalin given intramuscularly, and enzymes injected into and around the tumor
[10]
Inactive
[19]
Modest tumor growth inhibition in mice receiving 300 mg/kg intraperitoneally daily for 14 days
Human Studies
Reference
Study Results
Moertel CG, Ames MM, Kovach JS, et al.: A pharmacologic and toxicological study of amygdalin. JAMA 245 (6): 591-4, 1981. [PubMed] [Reference list]
Clinical Study only assessed appropriate dosing
Moertel CG, Fleming TR, Rubin J, et al.: A clinical trial of amygdalin (Laetrile) in the treatment of human cancer. N Engl J Med 306 (4): 201-6, 1982. [PubMed] [Reference list]
“No substantive benefit was observed in terms of cure, improvement or stabilization of cancer, improvement of symptoms related to cancer, or extension of lifespan”. Data is below:
[1] https://www.researchgate.net/publication/274868430_Amygdalin_in_Bitter_and_Sweet_Seeds_of_Apricots [2]https://recalls-rappels.canada.ca/en/alert-recall/health-canada-sets-new-cyanide-limit-mitigate-risks-associated-eating-apricot-kernels [3] Moertel CG, Ames MM, Kovach JS, et al.: A pharmacologic and toxicological study of amygdalin. JAMA 245 (6): 591-4, 1981. [PUBMED Abstract] [4] Moertel CG, Fleming TR, Rubin J, et al.: A clinical trial of amygdalin (Laetrile) in the treatment of human cancer. N Engl J Med 306 (4): 201-6, 1982. [PUBMED Abstract] [5] https://www-ncbi-nlm-nih-gov.ccnm.idm.oclc.org/pmc/articles/PMC5623210/ [6] https://www.njmonline.nl/getpdf.php?id=1379 [7] https://www.canada.ca/en/health-canada/services/food-nutrition/reports-publications/food-safety/cyanide-bitter-apricot-kernels.html [8] https://www.cancer.gov/about-cancer/treatment/cam/hp/laetrile-pdq