The substance commonly referred to as “Vitamin B17” is one of the most contentious subjects in nutrition and health. Despite its popular designation, this compound is not recognized as a vitamin by scientific bodies and has generated controversy due to its chemical properties. This article clarifies the nature of this substance, its true identity, and the specific foods where it is naturally present.
Defining Amygdalin and the B17 Misnomer
The chemical compound often mislabeled as “Vitamin B17” is scientifically known as amygdalin. Amygdalin is classified as a cyanogenic glycoside, a naturally occurring molecule found in various plants. The name “Vitamin B17” is a misnomer, as this substance does not meet the scientific criteria for a vitamin.
Chemically, amygdalin has the formula C20H27NO11. Its structure includes a cyanide-containing group attached to two sugar molecules. This structure is the root of its biological effect, as the bound cyanide can be released under specific conditions. The compound was erroneously designated as a pseudo-vitamin in the 1950s in connection with its semi-synthetic derivative, Laetrile.
Laetrile is a modified version of amygdalin that was promoted for decades as an alternative therapy. This promotion led to the widespread adoption of the “Vitamin B17” terminology. The scientific community consistently refers to the compound by its chemical name, amygdalin, emphasizing that neither it nor Laetrile is a vitamin. The compound’s classification as a cyanogenic glycoside indicates its potential to produce the toxin hydrogen cyanide.
Natural Dietary Sources of Amygdalin
Amygdalin is most concentrated in the seeds and kernels of fruits belonging to the Prunus genus, which are part of the rose family (Rosaceae). These stone fruit pits represent the richest dietary sources of the compound. Apricot kernels, in particular, can contain high concentrations, sometimes measured at approximately 14 grams of amygdalin per kilogram of kernel.
The kernels of peaches, plums, and cherries also contain noteworthy amounts of this cyanogenic glycoside. Peach kernels may contain up to 6.8 grams per kilogram, while plum kernels range from 4 to 17.5 grams per kilogram, depending on the variety. Consuming the kernels of these fruits, rather than the surrounding pulp, is where the risk of exposure to high levels of amygdalin lies.
Outside of the Prunus family, amygdalin is present in certain nuts and seeds. Bitter almonds are a well-known source, containing a significantly higher concentration of the compound compared to the sweet almonds typically consumed. Bitter almonds can have concentrations between 33 and 54 grams per kilogram, while sweet almonds average a mere 0.063 grams per kilogram. The presence of amygdalin in these foods is a natural defense mechanism for the plant, acting as a deterrent to insects and herbivores.
Other plants that contain amygdalin or related cyanogenic glycosides include:
- Flaxseeds.
- Certain varieties of lima beans.
- Clover.
- The roots of manioc (cassava).
Understanding Cyanide Toxicity
The primary health concern associated with consuming amygdalin-rich foods is the risk of cyanide poisoning. When amygdalin is ingested, enzymes in the digestive tract, particularly beta-glucosidase found in the gut and released by chewing the seeds, break the compound down. This chemical reaction releases hydrogen cyanide (HCN), a potent respiratory toxin.
Hydrogen cyanide works by inhibiting a specific enzyme called cytochrome oxidase within the cells, which prevents the body from using oxygen. The symptoms of acute cyanide poisoning can manifest quickly, ranging from mild effects such as headache, dizziness, and nausea to more severe conditions. High doses can lead to confusion, difficulty breathing, dangerously low blood pressure, seizures, coma, and death.
Toxicity is highly dose-dependent, meaning the amount consumed directly relates to the severity of the reaction. It is estimated that consuming as few as 5 to 10 bitter almonds can be poisonous for a child, and around 50 bitter almonds may constitute a lethal dose for an adult. The risk is particularly high when consuming raw kernels, especially those that have been crushed or chewed, which facilitates the enzymatic breakdown.
The synthetic derivative, Laetrile, was promoted as an unproven cancer treatment. However, large-scale clinical studies consistently failed to demonstrate any effectiveness against cancer. Due to the lack of evidence for benefit and the significant risk of cyanide poisoning, the U.S. Food and Drug Administration (FDA) has not approved Laetrile as a medicinal product.