For some years, scientists have argued over whether a chemical, called 4-methylimidazole (4-MI), that gives colas their characteristic caramel color, poses a cancer risk to humans. The latest example is a study, published in 2015 by researchers at Johns Hopkins in conjunction with US Consumer Reports, that called for action to reduce the amount of 4-MI in various soft drinks. Once more there was a swift rebuttal from industry; moreover, the FDA, which has been studying 4-MI for several years, does not believe that there is yet enough scientific evidence on which to act, so the argument continues to go round and round. Here is an examination of the issue that I posted on CTV.ca/health in 2011.
Does the colour in cola cause cancer? A reality check
by Dr. Lorne Brandes February 23, 2011
First, I must make the following disclosure: I can’t remember the last time I drank a Coke, Pepsi or any other brand of cola. If it had to depend on me, the soft-drink industry would not exist.
Second, I must share a fond, but quirky, memory with you. Back in my medical school days, I had a wonderful professor of dermatology, the late Dr. William (Bill) Pace, who introduced my wife and me to his favorite dessert, a delicacy his family unappetizingly dubbed “boiled can”.
Its name was derived, literally, from boiling a small unopened can of Carnation condensed milk in a pot of water for a precise number of minutes. After cooling the can to room temperature, the lid was opened and the container overturned on a plate. Out plopped a light brown-coloured pudding with an out-of-this-world taste.
“Boiling turns the sugar in the milk to caramel, but you mustn’t overboil it or the whole thing will turn dark and bitter,” Bill explained.
Such was my unexpected introduction to the process of caramelization, a chemical reaction that results when various types of sugar (fructose and glucose, for example) are heated to form caramel, the substance that imparts its distinctive, pleasantly sweet flavour to a wide assortment of food, candy and beverages.
In addition, caramel adds colour, ranging from gold to brown, to a wide range of products, from colas to Worcestershire sauce, coffee, wine and baked goods. However, to meet the many different uses of caramel by the food industry, its properties are manipulated by heating sugars with chemical additives, such as ammonia and sulfite, to form what are called “E150 caramels”.
For example, colas require negatively-charged caramel molecules, generated when ammonia is added to the sugar; otherwise, if positively charged, the caramel would react with phosphoric acid (the substance that gives colas their “tang”) and precipitate out of solution, resulting in a loss of the brown colour.
However, heating sugar in the presence of ammonia generates many other compounds in addition to caramel; among them are by-products called “methylimidazoles”.
Rodent studies carried out in 2008 by scientists at the U.S. Government’s National Institute of Environmental Health Sciences revealed that a two-year exposure to increasing concentrations of 4-methylimidazole (4-MI), present in colas, caused a significant increase in a type of lung cancer, called alveolar/bronchiolar carcinoma, in both male and female mice, but not in rats. There was a non-significant trend towards an increase in a type of leukemia in female rats, but no evidence of carcinogenicity in male rats.
Based on these findings, in 2009 the state of California posted its intention to list 4-MI as a carcinogen under the Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65).
Now, following California’s lead, a Washington, DC organization, called the Center for Science in the Public Interest (CSPI), has just petitioned the Food and Drug Administration (FDA) to “revoke regulations authorizing the use [of] caramel colorings that are produced by means of an ammonia or ammonia-sulfite process and contain 2-methylimidazole and 4-methylimidazole, both of which are carcinogenic in animal studies.”
"If consumers want another reason to avoid soda pop, this is a good one. It makes no sense to leave these in the food supply," the group's Executive Director, Michael F. Jacobson, commented.
The response from the beverage industry was swift: "The safety of our products is the foremost priority for our companies. Consumers can take confidence in the fact that people have been safely drinking colas for more than a century, as well as consuming the wide variety of foods and beverages containing 4-MI, from baked goods and breads to wine and coffee. 4-MI is found in trace amounts in a wide variety of foods and beverages, including Coca-Cola. In fact, it forms normally in the 'browning reaction' while cooking, even in one's own kitchen."
As for the FDA, in answer to an inquiry about the CSPI petition from a blog site called Consumer Ally, the agency noted that “its assessment [of the data] will dictate what, if any, regulatory action needs to be taken.” According to the website, in making this statement, the FDA acknowledged that 4-MI is on a list of chemicals to be reviewed for carcinogenicity by the World Health Organization’s International Agency for Research on Cancer.
What is the truth here? Clearly, 4-MI, a by-product of caramelization in the presence of ammonia, is a carcinogen in the mouse, but not in the rat. As for humans, who have been “safely drinking colas for more than a century”, who knows? There are no human studies of 4-MI from which to remotely glean an answer.
So, will the FDA act to remove the ammonia/caramel colouring from colas? Don’t bet on it.
The reality is that any cancer danger from non-diet Coke and Pepsi arises far less from their small content of 4-MI than from their astronomically high content of sugar. Published studies show that the daily consumption of sugar-rich soft drinks, colas among them, contribute significantly to the epidemic of obesity in our society. And make no mistake about it, up to half of all cancers, whether in rodents or humans, are directly related to obesity, and may be prevented by staying slim and trim.