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Carcinogen In The Cola: 4-Methylimidazole

What’s all the fuss about Pepsi and Coke products containing a caramel coloring agent called 4-Methylimidazole?

In March 2012, it was announced that both Coca-Cola and Pepsi have had their caramel color suppliers modify their manufacturing processes in order to meet the new California standard; as of the announcement the changes had already been made for beverages sold in California.

Coca-Cola and Pepsi have changed their recipe in order to avoid a cancer warning on the label, as shown in a Guardian report.

US Dept Of Health And Human Services Food And Drug Admin Report:

Barring the use of the caramel colorings produced with ammonia could prevent cancer in thousands of consumers. In addition, the FDA immediately should change the name “caramel coloring” to “chemically modified caramel coloring” or “ammonia-sulfite process caramel coloring” (and similar terms for other classes of the colorings) and should not allow products to be labeled “natural” if they contain any type of caramel coloring.

Caramel colorings are manufactured in several ways. Caramel Color I (may be used in high-proof alcoholic beverages) and Caramel Color II (may be used in cognac, sherry, and vegetable extract) are produced with alkali or acid caustic chemicals and sometimes sulfites (Caramel II), but not with ammonium compounds.5 Caramel Color III (synonyms: ammonia caramel, ammonia process caramel, closed-pan ammonia process caramel, open-pan ammonia process caramel, bakers’ caramel, confectioners’ caramel, and beer caramel) is prepared by the controlled heat treatment of carbohydrates with ammonium compounds. Caramel Color III is often used in baking, beer, soy sauce, gravy, and other products. Caramel Color IV (synonyms: ammonia sulfite process caramel, sulfite ammonia caramel, sulfite ammonia process caramel, acid-proof caramel, beverage caramel, and soft-drink caramel) is prepared by the controlled heat treatment of carbohydrates with ammonium-containing and sulfite-containing compounds. Soft drinks colored with caramel coloring generally are made with Caramel Color IV, which is generally used in colas and certain other soft drinks, and it also may be used in blended whiskey and general food applications. A key difference between Caramel III and Caramel IV is that Caramel III carries a positive ionic charge, while Caramel IV carries a negative charge. That difference renders them appropriate for use in different categories of foods.

Amounts of 4-Methylimidazole in Beverages

According to the National Toxicology Program (NTP), a division of the National Institute of Environmental Health Sciences (NIEHS), 2-MI and 4-MI have been identified as undesirable by-products in several food products, including caramel coloring, soy sauce, Worcestershire sauce, wine, ammoniated molasses, and caramel-colored syrups. However, only caramel colors (caramel colors III and IV) manufactured with ammonia or its salts contain measurable levels of 2- or 4-MI. Those substances have also been detected in mainstream and sidestream cigarette smoke.

In one recent study, researchers at the University of California, Davis, found 4-MI at levels of 0.30 to 0.36 micrograms/milliliter (ug/ml) in representative brands of colas that we presume included the two major U.S. brands, Coca-Cola and Pepsi-Cola. A 12-ounce serving of those drinks would contain 108 to 130 ug of the contaminant.

4-Methylimidazole is a Carcinogen in Animals


The NTP conducted a long-term feeding study (106 weeks long beginning with mice six weeks of age old) using 4-MI in male and female B6C3F1 mice.16 As shown in the Table below,17 in males, the high-dose group had a significant increase in the combined incidences of alveolar/bronchiolar adenoma or carcinoma (p < 0.01). In females, the combined incidences of alveolar/bronchiolar adenoma or carcinoma were significantly increased in the mid- (p < 0.001) and high-dose (p < 0.01) groups. In addition, the incidence of alveolar epithelial hyperplasia was significantly increased in high-dose females. The tumor incidence in treated females and males exceeded the NTP historical control incidence for combined alveolar/bronchiolar carcinoma or adenoma.

The NTP concluded: “There was clear evidence of carcinogenic activity of 4-methylimidazole in male and female B6C3F1 mice based on increased incidences of alveolar/bronchiolar neoplasms.”


Regarding the two-year feeding study of rats, the NTP concluded that, “The incidence of mononuclear cell leukemia in 5,000 ppm females was significantly greater than that in the controls, and the incidence slightly exceeded the historical range in feed study controls.” In addition, significant increases were observed in chronic focal inflammation of the lung, cardiomyopathy, focal atrophy of the pancreas acinus, and follicle mineralization of the thyroid gland.

Male rats did not experience significant increases in tumor rates, though chronic inflammation of the prostate gland and hypertrophy of the pituitary gland were seen.

In addition, abnormal behaviors, including hyperactivity, excitability, and impaired gait were seen in female rats, but not males, at some or all dosage levels in a dose-dependent way. Whether 4-MI is neurotoxic at the much lower doses to which humans are exposed is not known.

The NTP concluded:

There was clear evidence of carcinogenic activity of 2-methylimidazole in female 344/N rats based on increased incidences of thyroid gland follicular cell neoplasms. The increased incidences of hepatocellular adenoma in females may have been related to exposure. There was some evidence of carcinogenic activity in male B6C3F1 mice based on increased incidences of thyroid gland follicular cell adenoma and hepatocellular neoplasms. There was some evidence of carcinogenic activity in female B6C3F1 mice based on increased incidences of hepatocellular adenoma.


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