Reader Eric Ng wrote in to ask about the risk of apricot kernels causing cyanide poisoning, and whether the authorities should ban their sale in Singapore.

He purchased two packets of kernels after reading that they supposedly had anti-cancer properties. After more research, however, he found out that there were not only no anti-cancer properties, but also a risk of cyanide poisoning.

"I also noted that the health authorities elsewhere have issued warnings on the consumption of raw apricot kernels," said Mr Ng. "As this product is openly sold here as well, I wonder whether our health authorities have come out with similar warnings."

Journalist Jose Hong delves into the subject.

Apricot kernels - also known as "xing ren" in traditional Chinese medicine - are found inside apricot pits and contain the chemical compound amygdalin, which is converted to cyanide in the body.

The European Food Safety Authority says that eating more than three small kernels can exceed safe levels. Over-consumption has been linked to cyanide poisoning in Australia and Turkey.

According to the US Centres for Disease Control and Prevention (CDC), symptoms of cyanide poisoning include headache, dizziness, cardiac arrest and seizures.

Countries like Canada and the United Kingdom have issued health advisories on this food product.

In a statement to The Straits Times, the Toxicology Society (Singapore) said: "Cyanide compounds are known to be present naturally in some food substances like apricot kernels, almonds and even apples. Such food products have been consumed by many people with little ill effects. This is due to an inbuilt natural body process where enzymes are able to break down small amounts of cyanide."

The society said that while people have died or have been poisoned from eating foods that contain these cyanide compounds, it believes that "toxic effects from such food substances when consumed in small amounts are very rare".

"However, it has been reported that some individuals have been consuming large amounts of such food products as an alternative treatment to cancer. This has not been proven medically and can result in serious side effects," said the society.

The Straits Times found that apricot kernels are sold in stores like NTUC FairPrice, where they are marketed as "packed with natural enzymes and vitamins, namely vitamin B17, or amygdalin".

A spokesman for the supermarket chain said: "FairPrice works closely with the authorities to ensure the food in our stores are safe for consumption and we adhere to their guidelines and regulations with regard to all the products we stock in our stores,

"We are currently in contact with our supplier and the relevant authorities to seek further clarification on the sale of sweet apricot kernels in Singapore."

The Agri-Food and Veterinary Authority of Singapore has been approached for comment.

Apricot kernel is not the only plant product that can lead to cyanide poisoning. The seed of the kepayang tree's fruit, also known as buah keluak, contains the deadly poison when raw.

But when properly prepared, it transforms into a key ingredient in Peranakan dishes like ayam (chicken) buah keluak.