Substance that causes kidney stones found in food samples

Acid oxalic, which can cause kidney stones, has been found in many food samples, including rice vermicelli, peziza, instant noodles, and sponge cake, recent tests have found.  

The news was released by Professor Dr. Chu Pham Ngoc Son, deputy head of the Ho Chi Minh City Union of Scientific and Technical Associations, at a conference on food safety and nutrition related to acid oxalic, which is naturally found in some foods but can be made industrially.

Acid oxalic is a colorless, toxic organic compound widely used as an acid rinse in laundries for its effectiveness in removing rust and ink stains. It can also be used in paper production and processing.

This substance, made industrially, is banned by the Health Ministry from use as an additive in food production and processing in Vietnam.

Doctors advise that children and those who have a history of kidney stones should limit their intake of vegetables that are naturally rich in acid oxalic, such as roasted groundnuts (131mg/100g), amaranth leaf  (530mg/100g), bamboo shoots (333mg/100g), and roasted cashew nuts (263mg/100g).

From June to December 10, 2013, Sac Ky Hai Dang Science Technology Services Joint Stock Company analyzed 873 samples of various foods, including rice vermicelli, flour, instant noodles, fresh and dried bamboo shoots, peziza, sponge cakes, steamed rolled rice pancakes, and tea, Dr. Son said.

Of these samples, 363 (or 41.58 %) were found containing acid oxalic at high levels.

All nine samples of fresh bamboo shoots contained the acid (295 - 3.080mg/kg), and 25 of the 26 samples of salted bamboo shoots contained the substance.

Of the 353 samples of flour, 120 contained the acid with contents of 32.4 - 374mg.

Notably, all 62 samples of instant noodles, both locally produced and imported, were found containing acid oxalic with contents of 73.5 - 293mg/kg.

Since there are two kinds of acid oxalic, natural and industrial, the issue here is clarifying whether the above foods inherently contain natural acid oxalic or producers add industrial acid oxalic into their products during production or processing.

Risk

Dr. Le Truong Giang, chairman of the HCMC Public Health Association, said acid oxalic can combine with mineral salts such as calcium, magnesium, or potassium to form oxalate salts, causing a depletion of such necessary minerals in the body.

Meanwhile, oxalate salts can accumulate in the kidneys over time, and in certain conditions, they can form kidney stones.

In order to limit the risk of kidney stones, people can drink a lot of water to dilute their urine, reduce the oxalate salt content, and increase the pH level, Dr. Giang said.  

According to Dr. Du Thi Ngoc Thu of the Urinary Surgical Department at HCMC-based Cho Ray Hospital, natural acid oxalic is not harmful to people who eat normal portions of vegetables, cereals, or fruits.

Meanwhile, industrial acid oxalic, used as a bleaching agent in food production, is very harmful to human health, Dr. Thu said.

Extended exposure to food containing industrial acid oxalic can cause harm to the kidneys, liver, digestion system, and other organs, said Dr. Nguyen Thi Huynh Mai, deputy head of the HCMC Food Safety and Hygiene Sub-department.