Short answer
Cyanide is highly toxic, even in small amounts! A sudden overdose of this chemical disrupts the body's ability to convert oxygen into energy efficiently. Since the brain requires significantly more energy than other organs, it is affected more rapidly and severely by cyanide poisoning. Long-term exposure to small amounts of cyanide (such as that found in cassava) can also result in lasting neurological symptoms.
Longer answer
What exactly is cyanide?
Cyanide is a simple molecule made up of two atoms: carbon (C on the periodic table) and nitrogen (N). These atoms are joined by a triple bond, and the molecule carries a negative charge. Cyanide can bind with other molecules to form a gas (hydrogen cyanide, also known as prussic acid) or solids (such as potassium cyanide and calcium cyanide salts).
The gaseous form of cyanide is extremely lethal! For example, hydrogen cyanide was the active ingredient in Zyklon-B, used by the Nazis in gas chambers. Certain bacteria, fungi, and plants naturally produce solid forms of cyanide. Cyanide can be found in almonds, the seeds of some fruits, and cassava (a root vegetable commonly eaten in South America and Africa). That said, there’s no need to worry – when prepared correctly, these foods are completely safe to consume. A word of caution: consuming over a kilogram of almonds (roughly 1,000 nuts) in one sitting could result in mild cyanide poisoning!
Image 1: Cyanide is a molecule with a triple bond between carbon and nitrogen. Small amounts of cyanide can be found in almonds, apple seeds, peach pits, cherry stones, and cassava roots. Cassava is often processed into products like starch and flour.
What exactly does cyanide do to make it so deadly?
Cyanide molecules are absorbed by our cells (including brain cells) and bind to a specific protein in our mitochondria. Mitochondria are organelles – tiny ‘organs’ within our cells – often referred to as the ‘powerhouses’ of the cell. They produce energy using oxygen (in more detail, they convert ADP into ATP, the fuel our body uses). Cyanide binds to the protein cytochrome oxidase, blocking this process. The resulting lack of energy in the cells causes organ failure. The organs requiring the most oxygen – and thus the most energy – are the brain and heart. Consequently, cyanide ingestion can lead to a coma and, eventually, death. This is what occurs in cases of acute poisoning, such as swallowing a cyanide pill (a suicide pill containing potassium cyanide, used during the Second World War).
Image 2: A brain cell (left) contains small mitochondria (right), which constantly produce energy for the body. Proteins within the mitochondrial membrane (bottom) drive energy production. Cyanide (CN⁻, shown in red) binds to the protein cytochrome oxidase, blocking the conversion of ADP to ATP and thereby cutting off the body’s energy supply.
While the dangers of an acute, high dose of cyanide are clear, long-term exposure to lower doses can also lead to neurological issues. As previously mentioned, a concerning example is the cyanide found in cassava plants.
Cassava is cultivated across much of South America and Africa due to its high nutritional value. However, if improperly prepared, cassava can contain cyanide. This is particularly an issue in conflict zones, where food shortages force people to skip proper preparation methods. Two neurological disorders are associated with poorly prepared cassava: myeloneuropathy and Konzo.
Myeloneuropathy affects the spinal cord, causing problems with sensation, vision, hearing, and balance in adults, particularly among older individuals who consume cassava as a staple food. Konzo causes sudden muscle weakness due to damage to upper motor neurons, leading to irreversible movement disorders such as permanent paralysis.
Both conditions highlight the importance of proper food preparation to prevent neurotoxic effects. It remains unclear whether long-term consumption of small amounts of cyanide has more subtle effects on the nervous system – this is currently under investigation.
Cyanide, depending on the dose, has profoundly adverse effects on the body. In cases of acute, high-dose exposure, the disrupted energy supply leads to organ failure. The brain, with its high energy demands, is one of the first organs to be affected. Long-term exposure to lower doses can also result in brain damage, as seen in cases of improperly prepared cassava. But don’t worry – this won’t happen with the cassava crisps from Albert Heijn. However, you may now view a kilo of almonds in the same supermarket differently – not just because of the price…
Further reading:
https://www.youtube.com/watch?v=c6i63BhBt5Q
Newton, C.R., 2017. Cassava, konzo, and neurotoxicity. The Lancet Global Health, 5, pp.853-854.
Tshala‐Katumbay, D.D., Ngombe, N.N., Okitundu, D., David, L., Westaway, S.K., Boivin, M.J., Mumba, N.D. and Banea, J.P., 2016. Cyanide and the human brain: perspectives from a model of food (cassava) poisoning. Annals of the New York Academy of Sciences, 1378, pp.50-57.