Just four years ago, on the Thursday morning of 25 April 2002, millions of people awoke to newspaper and TV reports that their breakfast might be laced with a deadly chemical.
They hadn’t been poisoned, nor were they victims of an unscrupulous food manufacturer. Nevertheless, the reports warned, the slice of bread, bowl of cereal or plate of waffles in front of them might contain a potent cancer-causing chemical called acrylamide. The implications were astounding. Scientists said the chemical might be impossible to eradicate, as it was created during the normal cooking process. And the health effects were impossible to judge.
Though the story faded from the front pages, 91av can reveal the unprecedented research effort that is under way to learn more about acrylamide. The twin goals are to establish whether it might be responsible for an epidemic of cancer and other illnesses, and to eliminate acrylamide as far as possible from our food. Andy Coghlan takes up the story of one of the biggest food scares of modern times.
Advertisement
NO ONE expected the news delivered by Leif Busk and Margareta Törnqvist on 24 April 2002. Speaking in Sweden to the biggest press conference the country had seen for almost 20 years, the two scientists announced to the world that the toxic industrial chemical acrylamide was lurking in a huge range of everyday foods.
“It was a complete bolt from the blue,” recalls Diane Benford, head of the UK Food Standards Agency’s toxicology branch. The discovery meant that almost everyone must be ingesting this toxic substance, with unknown consequences for public health. “Acrylamide was suddenly discovered in food, whereas previously, it was only known as an industrial chemical. It was unprecedented,” she says.
The reaction to the news was unprecedented too, starting with the huge press interest in the announcement. “What we wanted to bring out by holding the press conference was that we needed more data,” says Busk, who is still based at Sweden’s National Food Administration in Stockholm. What resulted was a global media frenzy, followed by fearful consumers demanding to know what foods, if any, were safe to eat. “We didn’t anticipate the information vacuum that would result.”
Governments, international health authorities and the food industry reacted quickly. In June 2002, the World Health Organization convened a summit on acrylamide in Geneva, Switzerland, which revealed how little we knew about the chemical and its effects. Since then, tens of millions of dollars have been spent on hundreds of research projects to find the answers, and next week scientists will come together to discuss progress at a meeting convened by the UN’s food regulator, the Codex Alimentarius Commission.
What is clear is that acrylamide is formed by what is known as the Maillard reaction, in which amino acids react with sugars when food is heated to more than 120 °C and begins to brown. Bread crusts and fried or roasted potatoes are among the many foods in which the Maillard reaction is responsible for the characteristic texture and taste. Acrylamide forms from the reaction between the amino acid asparagine and reducing sugars such as glucose and fructose, which are found in large quantities in plants such as potatoes and cereals.
The current best guess is that half the acrylamide we ingest comes from processed foods, and half from food cooked at home. Richard Stadler, technical director of an initiative by the European Union’s Confederation of the Food and Drink Industries (CIAA) to eliminate acrylamide from processed food, says research is ongoing to pin down exactly where the acrylamide in our diet comes from.
It is also becoming apparent that acrylamide might be far more prevalent in food than even the Swedish researchers thought. According to data from 17 countries published in February 2005 by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) we now know that the chemical is found in foods ranging from olives, pizza and beer to baby foods and green tea. Between 10 and 20 per cent of our exposure is thought to come from pastries and cookies, while in some countries up to 39 per cent of exposure comes from coffee (see Table).
That puts acrylamide in a different category from carcinogens in food such as aflatoxins or ochratoxin A, which are produced by fungi that contaminate cereal crops. For these toxins, legal safety levels can be set on the quantities that can be present in food, ensuring that only safe levels are ingested. That is virtually impossible with acrylamide, as it is everywhere. “We realised we couldn’t remove products containing it from sale,” says Busk. “There would be nothing left in the shops.” Even if that were done, acrylamide would still be produced during home cooking.
Acrylamide is known to have potent health effects. It is potentially neurotoxic, and workers in the building and construction industry exposed to polyacrylamide, which is prepared on site from acrylamide, have developed numbness in their fingers and toes, while prolonged exposure can trigger paralysis, Busk says.
Animal studies suggest that a substance called glycidamide, produced by the body as it breaks down acrylamide, is genotoxic, as it can bind to and damage DNA. “What that means is complicated,” says Angelika Tritscher, WHO secretary to JECFA. In people, less glycidamide appears to be produced when acrylamide is broken down than in animals, she says, so we may be less affected. In 2004, a US Food and Drug Administration expert panel concluded there was a negligible risk that acrylamide would trigger adverse reproductive and developmental effects in people, while there was only a “minimal concern” that it would cause heritable effects in the general population.
The most controversial area of research relates to whether acrylamide in food can cause cancer. Rats fed acrylamide develop tumours in the mouth, and the mammary, thyroid and pituitary glands. Yet most epidemiological studies in people so far have found no such link. “Our series of large case-control studies found no consistent association between dietary acrylamide intake and risk of breast, colorectal or other common cancers,” says Claudio Pelucchi of the Mario Negri Institute of Pharmacological Research in Milan, Italy (International Journal of Cancer, vol 118, p 467). “In two previous investigations we found no association between risk of selected cancers and consumption of fried or baked potatoes and coffee – two of the food items thought to contribute a considerable risk.” His negative findings were echoed by those of a team in 2003 led by Lorelei Mucci of the Harvard School of Public Health, published in the British Journal of Cancer (vol 88, p 84).
Despite these reassuring signs, the JECFA concluded last year that efforts to reduce acrylamide should continue. It cited data showing that, on average, people eat 1 microgram of acrylamide per kilogram of body weight per day. That is 1/300th of the dose known to cause a 10 per cent increase in breast cancer in rats, and high consumers of acrylamide might be eating 1/75th of the carcinogenic dose. In the world of food safety, that is seen as an uncomfortably narrow safety margin. For instance, people eat between 1/10,000th and 1/25,000th of the safe dose of the carcinogenic polyaromatic hydrocarbons formed in foods such as charred burgers every day.
According to Busk, any cancers caused by acrylamide in food will only show up in sophisticated, large epidemiological studies, and these have not been done. “The risk is low compared to smoking, but high compared with other food carcinogens,” he says. “It’s probably the same level of risk as background natural radiation.”
We might know for sure in two or three years, when the results of a massive toxicology programme in animals initiated in 2004 by the FDA bears fruit. A genotoxicity study in animals is just complete, and should be published soon, while carcinogenicity studies are due to be completed in 2007, with neurotoxicity studies due in 2008. “We don’t take issue with the JECFA conclusions, but the FDA data in the next two years will be crucial to moving beyond the interim levels at the moment,” says the FDA spokeswoman on acrylamide. The JECFA agrees, and has said it will review its recommendations in the light of the FDA animal studies.
In the meantime, behind the scenes, the food industry has made massive strides towards reducing levels of acrylamide in the foods we buy. Millions of dollars have been spent reducing levels of it in fries, potato chips, bread, biscuits, gingerbread and coffee, while last year the CIAA set up a website, aimed at both food manufacturers and home cooks, advising on how best to eliminate acrylamide from food (see “The golden rule”). “If it’s later found not to be a concern, then we may have spent money on it, but at least no lives will have been lost through negligence,” Benford says.
“Behind the scenes the food industry has made great strides towards reducing the levels of acrylamide in the food we buy”
The advice of most experts is to continue to eat a balanced diet low in fried foods and high in fruit and vegetables, which is what most also advise on nutritional grounds. Busk, the man who helped alert the world to the problem four years ago, is certainly not going to extremes. “I eat fewer crisps and fries, but still drink as much coffee, and that’s 30 to 40 per cent of the exposure,” he says. “It’s important to put it all in perspective.”
How it began
The acrylamide scare began in 1997, when a herd of cows on the remote Bjäre peninsula in southern Sweden began to stagger, collapse and die. Investigations revealed the cattle had been drinking from a stream laced with acrylamide, which had leached from drilling works on a nearby mountain tunnel where polyacrylamide was being used as a sealant for cracks.
“The levels were very high in the stream,” says Leif Busk of Sweden’s National Food Administration, who five years later helped break the news of acrylamide’s widespread presence in food. “You could see pictures on TV of these cows falling over and behaving in a peculiar way, almost like they had BSE.” Swedish viewers were disturbed by what they were seeing, and even more alarmed when they learned that a common industrial chemical was to blame. “That sensitised the Swedes to acrylamide, and played a role in the frantic reaction later on,” he says.
The drilling company called in Margareta Törnqvist of the University of Stockholm to check if its workers had been exposed to the chemical, and she tested their blood for acrylamide. It was when she found unexpectedly high levels of the chemical in a control group with no known exposure to industrial acrylamide that she began to wonder whether foods were the source. She initially suspected burgers might be to blame, until tests revealed high levels of acrylamide in potato products.
At first these results were greeted with disbelief. “The levels found by Törnqvist were so high in fried potatoes, French fries and crisps, we suspected it must be an artefact,” Busk says. Only when the tests were repeated and extended, and the researchers were sure, did they make their findings public.
The golden rule
One way to limit the amount of acrylamide produced in home-cooked foods is to follow the “golden rule”. That means cooking or baking foods only until they are golden, and not letting them go brown or black.
Acrylamide forms at temperatures above 120 °C from reactions between the amino acid asparagine and reducing sugars such as glucose or fructose. This is the so-called Maillard reaction, which a whole range of amino acids undergo to create the rich flavours of grilled, baked and roast food. It is also what causes food to brown, and the browner the surface the higher the acrylamide content.
Following the golden rule has its downsides. Potato products cooked at lower temperatures tend to absorb more fat, and so are less nutritionally healthy. Also, gentle cooking is more likely to allow bacteria to survive, raising the risk of food poisoning. “You can’t just get rid of acrylamide, because you can’t get rid of heat treatment for safety and quality reasons,” points out Angelika Tritscher, the WHO’s secretary to JECFA. “It’s a trade-off.”
Steps taken by the food industry to limit acrylamide include selecting different potato varieties, as levels of the reducing sugars that contribute to acrylamide formation can vary 30-fold across varieties. Developing new yeasts that limit the content of asparagine formed in dough can cut down the amount of acrylamide in bread crusts. Several companies have been experimenting with asparaginase, an enzyme that destroys asparagine and which could be commercially available by the end of the year.
More details are available at .
