Laetrile (Vitamin B17)

Laetrile is a purified derivative of a naturally occurring compound called amygdalin, which is found in the pits of many fruits, raw nuts and other plants [1]. Amygdalin, also called vitamin B17, is present in high amounts in apricot kernels, which are commonly believed to have anticancer properties. As an alternative treatment for cancer, laetrile is highly controversial. Proponents claim it has potential therapeutic anticancer effects, while others highlight the lack of research and risks of toxic side effects.

The potential health benefits of vitamin B17 containing foods are not a recent discovery. The anticancer properties of amygdalin are documented in ancient Egypt and traditional Chinese medicine. It is hypothesized that consumption of foods high in vitamin B17 may be responsible for certain cancer-free tribes, such as the Hunza, who eat large amounts of apricot kernels.

Laetrile is theorized to prevent cancer development and eliminate cancer cells through the production of hydrogen cyanide. Hydrogen cyanide is proposed to selectively target and destroy mutated cells (with altered or damaged DNA) [3]. Laboratory research exists to support the potential anticancer properties of laetrile [4] [5]. However, clinical research in humans is still lacking.

There has been significant controversy surrounding the use of laetrile as a cancer treatment due to the cyanide toxicity causing potential of amygdalin. Proponents of the therapy claim that toxic effects of laetrile occur only when ingested orally and in dangerously large doses [2]. However, there is scarce scientific evidence to evaluate the safety and efficacy of laetrile with any high degree of certainty. Further, research in humans is still needed.

History of Laetrile (B17)

Amygdalin was isolated for the first time by two French chemists in the 1830s. Records of its use as an anticancer therapy date back as early as 1845 with positive results reported in patients in Russia [6]. It was first used for cancer in the United States in the 1920s, but in pill form and deemed too toxic. In the 1950s, a semi-synthetic and purified derivative of amygdalin was patented by Ernst T. Krebs under the name Laetrile, which when given intravenously was claimed to be non-toxic [6].

The ‘War on Cancer’ in the USA began in the 1970s, which led to investigations into new treatments to fight the disease. Memorial Sloan Kettering Cancer Center in New York began research into laetrile. Dr. Kanematsu Sugiura, an esteemed pioneer in the field of cancer research and co-inventor of chemotherapy, found that when he used laetrile on mice it tended to inhibit the growth of secondary tumors (although it did not destroy the primary tumor) [9].

Dr. Sugiura was able to repeat his findings many times over several years with the same positive results in his research. However, despite being renowned as an extraordinarily reliable and trustworthy scientist, his research was reportedly suppressed [9] [19]. Ralph W. Moss, a science writer at Sloan Kettering made an attempt to publicize the research and leaked Dr. Sugiura’s findings to the American public, but he was apparently fired by the company as a result of his actions [10] [19].

At the time Sloan Kettering was the world’s leading manufacturer of chemotherapy. Dr. Sugiura’s original findings were never published by the institute. Instead, they published results from colleagues who claimed to have followed the same protocol, but found no benefits [11]. Dr. Sugiura stood behind his findings and continued to believe that laetrile could have potential therapeutic applications, notably in cancer prevention and palliative care to slow the spread or progression of the disease [12].

Despite pressure from the public to make it available during the 1970s, laetrile was banned in 1980 [6]. In 1982, the Mayo Clinic conducted a clinical trial on laetrile and concluded it was ineffective and toxic [13]. They claimed that further investigation into its potential anticancer effects were not justified [14]. The results were considered conclusive. However, there were allegedly flaws in the research methods of the Mayo Clinic related to the type of laetrile used, the way it was administered, the use of terminal patients and the way in which the results were interpreted [14].

The Mayo Clinic study sparked widespread belief in the medical community that laetrile was ineffective and toxic. To date, these are still the only clinical trials conducted on laetrile in humans. According to alternative sources, this research may have given an overly pessimistic view of the safety profile and potential efficacy of laetrile as a cancer treatment [14].

Research on Laetrile (B17)

Laetrile has been widely used across the world as an alternative cancer treatment [6]. However, despite numerous anecdotal reports of benefits, there have only been two clinical trials published on laetrile as a cancer treatment for humans [13] [20]. These studies concluded that laetrile was not effective for cancer and potentially toxic for humans [13] [20]. However, criticisms have been made of this research and the design of the studies [14]. To date, there has never been a controlled clinical trial conducted on laetrile [6]. Further well-designed clinical research is still needed to better determine if anecdotal reports and claims of therapeutic benefits by proponents are valid.

A 2019 review explains that recent preclinical in vitro (laboratory) research shows that amygdalin does have anticancer properties and kill cancer cells [1]. However, the results of in vivo (animal) studies indicate that amygdalin is only minimally effective [1]. On the other hand, the review concedes that many case studies describe the antitumor effects of amygdalin [1]. However, anecdotal reports have not yet been validated by clinical trials. Therefore the treatment cannot be safely recommended for cancer patients based on current scientific evidence [1].

Data from a 2018 review of the published scientific literature confirms that apoptosis (programmed cell death) is a central process activated by amygdalin in cancer cells [2]. It provides a complete interpretation of the known anticancer mechanisms of amygdalin. The review explains that it may have a possible role in the fight against cancer by blocking cancer cell proliferation and growth [2]. It also states that there are mistaken beliefs surrounding the cyanide toxicity causing potential of amygdalin [2].

Another 2018 review also concluded that in vitro (test tube) experiments show that amygdalin induces apoptosis (cell death) in cancer cells [5]. Amygdalin has also been shown to inhibit the adhesion of breast cancer cells, lung cancer cells, and bladder cancer cells by decreased expression of specific pathways such as Akt-mMTOR. This mechanism of action could potentially lead to inhibition of metastases (spread of cancer cells) [5]. Amygdalin has also been shown to inhibit cell proliferation in renal (kidney) cancer cells [5].

A 2020 study concluded that amygdalin is a natural anticancer agent that promotes apoptosis and cell cycle arrest in hepatocellular carcinoma (liver cancer) cells [4]. The results of a 2013 study on amygdalin in human cervical cancer cell lines indicate that amygdalin could potentially provide therapeutic benefits for patients with cervical cancer [7]. A 2016 study demonstrates that amygdalin induces apoptosis and inhibits adhesions of triple negative breast cancer (TNBC) cells. The results support the potential therapeutic application of amygdalin as a chemopreventive agent or to alleviate progression of TNBC [8].

Furthermore, preclinical research shows that amygdalin in laetrile reduces the expression of pro-inflammatory cytokines, has an anti-inflammatory effect and activates muscle cell growth. These results indicate other potential benefits for cancer patients, especially in terms of palliative care and disease management [5].

In summary, the latest scientific research on laetrile suggests that its active compound amygdalin could potentially be applicable in the treatment or management of various cancer types and that its cyanide toxicity causing potential may be misunderstood. However, clinical trials still need to be conducted in humans to confirm safety and efficacy of the treatment. Preclinical research must be validated in animal models and then human clinical trials before it can be recommended for use in cancer patients. Currently, research is still lacking on laetrile.

Potential Applications of Laetrile (B17)

Initial cellular studies indicate that amygdalin (active component in laetrile or B17) could potentially have therapeutic applications in the treatment of various types of cancer [5]. Preclinical research demonstrates anticancer effects on a range of cancer cell types [5]:

• Lung [5]
• Bladder [5]
• Breast [17]
• Uterine [2]
• Stomach [2]
• Esophageal (throat) [2]
• Cervical [7]
• Kidney [5]
• Liver [4]

However, there is a lack of clinical research in humans to verify if preclinical research and the anticancer properties of amygdalin translate into an effective cancer treatment in humans.

Laetrile, or vitamin B17, is also claimed to interact with other antioxidants such as vitamin A, C, E and pancreatic enzymes, which help to break down and eliminate harmful mutated cells in the body [15]. The purported benefits of vitamin B17 include supporting detoxification, boosting the immune system, reducing oxidative stress and helping to prevent various disease processes [16]. However, these claims are not necessarily supported by clinical research.

Anecdotal reports and preclinical research indicate that laetrile could potentially play a role in cancer care. The following potential therapeutic effects of laetrile have been shown in early research or case reports, but are not currently validated by clinical research:

• Selectively destroys cancer cells
• Inhibit new cancer cell growth
• Prevent metastases (stop cancer spreading)
• Enhance immune function
• Improve detoxification
• Reduce inflammation
• Increase antioxidant activity
• Rebuild muscle and healthy tissues
• Slow progression of disease

Laetrile can be administered orally with a pill or by injection, either into the muscle (intramuscular) or directly into the veins (intravenous) [6]. It is most commonly applied intravenously followed by oral maintenance doses [6]. It is considered to be a nitriloside (a substance that naturally contains a poisonous substance called cyanide), which has given rise to some concerns about potential toxicity [3].

The incidence of cyanide poisoning is significantly higher when taken orally, because intestinal bacteria contain enzymes (beta-glucosidases) that trigger the release of cyanide [6]. However, when laetrile is administered intravenously, relatively little is broken down into hydrogen cyanide, because intestinal bacteria and their cyanide releasing enzymes are not involved in digestion [6].

With intravenous application conversion to cyanide appears to occur at much lower levels [6]. According to the Mayo Clinic clinical trial reports in 1982, patients did not have elevated blood cyanide levels after IV treatment, but did exhibit higher levels after oral ingestion [13]. Proponents of laetrile have suggested that the Mayo Clinic trials used higher dosages compared to normal protocols and that oral laetrile was sometimes also given during the IV periods, which may have resulted in elevated blood cyanide levels and toxic side effects [14].

One proposed explanation (amongst other theories) for the potential mechanism of action behind the purported anticancer effects of laetrile is related to the enzymatic vulnerabilities of cancer cells. It is reported that cancer cells have higher levels of beta-glucosidase, an enzyme that releases hydrogen cyanide from amygdalin [2].

Cancerous cells also lack an enzyme called rhodanese, which is required to detoxify cyanide [2]. Cancer cells are therefore suggested to be more vulnerable to the toxic effects of laetrile than normal cells because of an imbalance in these two specific enzymes [6].

Amygdalin, the active compound of laetrile, breaks down into three components in the human body: glucose, hydrogen cyanide, and benzaldehyde. The breakdown product benzaldehyde has also been shown to inhibit cancer cell growth, which could also indicate a potential synergistic anticancer effect [6].

In light of their enzymatic differences, hydrogen cyanide is reportedly liberated in much greater concentration in cancer cells. Laetrile is therefore theorized to target cancer cells more specifically. Furthermore, if some hydrogen cyanide escapes from the cancerous cells, normal healthy cells with sufficient rhodanese enzyme activity are believed to be able to more easily convert it into a harmless compound called thiocyanate [2].

There is experimental evidence to support this theory, but it is not yet proven in humans [6]. Some researchers have demonstrated that hydrogen cyanide is also produced in healthy cells [5]. Therefore ingestion may carry certain risks and potential side effects for humans [5].

The proposed mechanism of action of laetrile against cancer is based only on preclinical research. Well-designed clinical research in humans is still required to gain better insight into the purported action of laetrile, safety profile, efficacy against cancer and potential therapeutic applications.

Risks and Side Effects of Laetrile (B17)

Oral ingestion of amygdalin in high doses can result in cyanide poisoning. This occurs as a result of the breakdown of the compound by certain enzymes in the intestinal bacteria [6].

The side effects of amygdalin can also be potentiated by concurrent ingestion of raw almonds, crushed fruit pits and vegetables containing beta-glucosidase (such as celery, peaches, bean sprouts, carrots) or by taking large amounts of vitamin C orally [6].

Taking laetrile by mouth in pill form, or high-dose vitamin B17 supplements, carries significantly higher risks with potentially worse side effects than intravenous administration [6].

Overdose, which is more common in the case of oral administration, can result in serious side effects linked to cyanide toxicity. Cyanide is a neurotoxin that causes the following effects [6]:

• Nausea and vomiting
• Headache
• Dizziness
• Cyanosis
• Liver damage
• Hypotension
• Ptosis
• Ataxic neuropathies
• Fever
• Mental confusion
• Coma
• Death