When scientists call a press conference, reporters usually expect a dramatic announcement. They’ve cloned a sheep. They think they’ve found a way to produce nuclear fusion in a test tube. They’ve completed sequencing the human genome. They’ve discovered why fewer socks come out of a washing machine than go in. But reporters attending the press conference called by Sweden’s National Food Administration in April of 2002 heard nothing of the sort. Researchers at the University of Stockholm, they were told, had discovered acrylamide in potato chips, French fries, and in a variety of other popular foods. “Acrylawhaaat?” the scribes pondered. Most had never before heard of the chemical they would soon help make into a household word. A dirty word!
Acrylamide was a known animal carcinogen, the spokesperson explained. It had been unexpectedly found in a number of common foods, and possibly could account for thousands of cases of human cancer every year. Now he had the reporters’ full attention. Chips and French fries, as well as some baked goods, had levels of acrylamide hundreds of times higher than the maximum allowed in drinking water, according to standards set by the World Health Organization. Why should there be any acrylamide in drinking water? Because “polyacrylamide” is commonly used in water treatment to coagulate and trap suspended impurities. While polyacrylamide is harmless, it is always contaminated with trace amounts of the material from which it is made, namely, acrylamide. There is no doubt that acrylamide fed in huge doses to rats can cause a variety of tumors, but health authorities agree that the 1 or 2 micrograms of the stuff that might be ingested daily from water with a maximum allowable concentration of 0.5 parts per billion (PPB) is far too little to have any effect. In other words, the benefits of using polyacrylamide to remove water pollutants greatly outweigh any risk it may introduce.
But the Swedish scientists weren’t talking about 0.5 parts per billion, they were talking about French fries that had over 400 PPB, and chips that had as much as 1,200 PPB! Such levels, they suggested, could cause cancer in humans. The acrylamide story made the headlines, causing panic in the supermarket aisles and in the boardrooms of food producers. Was this just another “scare-of-the-day” story, soon to be forgotten, or was it important enough to warrant real changes in our eating habits?
Before coming to grips with that question, let’s take a moment to explore how the information about the presence of acryl-amide in our food supply came to light in the first place. It all started in 1997, with some paralyzed cows in Sweden. Farmers in the Bjare peninsula began to notice that their cows could not stand up properly. When fish breeders found dead fish by the hundreds in their breeding pools, authorities began to suspect an environmental problem. It turned out that they were right. A tunnel was being built nearby, and it had been plagued by water leaks. To solve the problem, over 1,400 tons of a sealant made with polyacrylamide had been pumped into the cracks in the tunnel. Since scientists had long known that high concentrations of acrylamide could affect the nervous system, the paralyzed cows and dead fish suggested that the chemical had leached out into the water table. Further investigation revealed that it was not only cows and fish that were affected, but also tunnel workers, who complained of feeling numbness in their extremities! As can be expected, this terrified the locals and caused cattle to be slaughtered, milk products to be dumped, and vegetables to be thrown away for fear of acrylamide contamination.
This is when Margareta Tornquist of the University of Stockholm got into the game. She had been asked to investigate the extent to which tunnel workers had been exposed to acrylamide. Blood samples were taken and analyzed for the presence of the chemical. For comparison, Tornquist also looked at samples taken from the general Swedish population. The results were stunning! As expected, the tunnel workers had high blood levels of acrylamide, but so did the others. Where was it coming from? Swedish water did not have unusual levels of acryl-amide, so the suspicion turned to the food supply. That’s when Tornquist discovered acrylamide in chips, fries, breads, cookies, and crackers. As it turns out, it forms naturally in starchy foods that are fried in fat at a high temperature. When rats were fed such foods, acrylamide was found in their blood at much higher levels than when they were fed boiled foods. A frightening picture began to emerge. A carcinogen, formed in significant amounts in common foods, could end up in the blood and be distributed through the body. According to the Swedish National Food Administration, the world needed to be informed of this risk, so it decided to call a press conference.
But wait a minute here. There is no evidence that acrylamide is a human carcinogen. While it is a well-established neurotoxin, a long-term study of over 8,000 workers who manufacture the substance, and therefore have huge exposures, found no link to cancer. Furthermore, it should be understood that our food supply is filled with natural carcinogens. Aflatoxins in peanuts, ethanol in wine, urethane in sherry, styrene in cinnamon, and heterocyclic aromatic amines in beef bouillon are as carcinogenic to rodents as is acrylamide. But we don’t eat isolated ingredients; we eat food. And food has numerous anti-carcinogens as well. Broccoli, onions, soybeans, flaxseed, and apples all contain compounds with decided anti-cancer activity. The bottom line, then, is that there is no scientific justification for the statement that acrylamide in food causes thousands of cases of human cancer. On the other hand, there is plenty of scientific justification to recommend cutting back on fatty, fried foods such as chips and fries, for a variety of reasons. So if fear of acrylamide causes people to do that, they will indeed be better off.
In any case, the food industry has responded to the acrylamide issue by mounting a variety of studies to explore just how acrylamide forms during baking, and how levels can be reduced. It didn’t take long to discover that the backbone of the acrylamide molecule comes from an amino acid called asparagine. When heated in the presence of glucose, asparagine undergoes a series of reactions that eventually liberate acrylamide. Food chemists now went to work and found that baking or frying at lower temperatures (below 175°C, or 347°F) significantly reduced acrylamide levels, which could be even further lowered by adjusting recipes or cooking conditions. For example, when sodium hydrogen carbonate (baking soda) is used to replace ammonium hydrogen carbonate as a baking agent in gingerbread, acrylamide concentrations are reduced by more than 60 percent. Blanching potato chips in a dilute acetic acid solution before frying leads to large decreases in acrylamide content. Many such changes have already been instituted, and an expert panel commissioned by the National Toxicology Program of the National Institute of Environmental Health Sciences now estimates that we ingest roughly 0.43 micrograms of acrylamide per kilogram of body weight a day in our diet, which is well below the amounts that cause cancer in laboratory animals.
We can also take some comfort in a recent joint study conducted by the Harvard School of Public Health and the Karolinska Institute in Sweden, which found no link between the consumption of acrylamide and the occurrence of colon, bladder, or kidney cancers. The study’s researchers, who reported their results in the British Journal of Cancer in 2003, performed what is known as a case-control study. They examined the dietary intake of acrylamide among 987 cancer patients and compared it to that of 538 healthy people to see if they could find a link between the disease and the chemical. No such link was apparent: the cancer patients had consumed no more acrylamide than had the healthy subjects. In fact, they associated higher levels of acrylamide in the diet with a lower, not higher, risk of colon cancer. Still, we are not yet ready to declare acrylamide an anticarcinogen. In all likelihood, foods that contain acrylamide also contain other ingredients, such as fiber, which may offer protection against cancer. An Italian study came up with similar results. An examination of over 7,000 cancer victims showed no evidence of a link to consuming fried or baked potatoes.
The question of a link between breast cancer and acrylamide has also been examined in light of the fact that high doses increase the risk of mammary tumors in rats. A Swedish study, published in the Journal of the American Medical Association in 2005, found no evidence of a connection after having followed over 43,000 women with an average age of thirty-nine for eleven years. Based on food frequency questionnaires at the beginning of the study, the women were divided into five categories that reflected their intake of acrylamide. Almost 700 women were eventually diagnosed with breast cancer, but there was no significant difference in the risk of the disease relative to the amount of acrylamide consumed.
Finally, let me call your attention to a paper published in the American Journal of Clinical Nutrition, which didn’t get nearly as much attention as the acrylamide story. Researchers at Tulane University studied over 9,000 people for roughly twenty-five years and found that those who consumed more than three servings of fruits and vegetables a day had an almost 30 percent lower risk of strokes and heart disease than those who ate less. They didn’t call a press conference . . . but should have.