4-Methylimidazole – A Cause for Concern in Caramel Colouring?

June 13, 2012 By

4-Methylimidazole is a substance found in caramel colouring that is manufactured using ammonia or ammonia sulphate in the production process. In addition to its presence in some soft drinks, 4-methylimidazole may be found in other food and beverage products such as coffee, breads, soy sauces, Worcestershire sauce, and other products, where food processing may lead to the formation of this substance (Office of Environmental Health Hazard Assessment (OEHHA), 2012; Chan et al., 2008). For example, 4-methylimidazole may form in the ‘browning’ process of certain food ingredients, also known as the ‘Maillard reaction’ in chemistry terms. This reaction occurs between carbohydrates and amino-containing compounds (Dills, 1993). Exposure to 4-methylimidazole may also occur in other industries, for persons who work in the pharmaceutical, dye, rubber industries, or who work with livestock feed that has been treated with ammonia (OEHHA, 2012).

In March of this year, Cola-Cola Co. and PepsiCo Inc. reduced the level of 4-methylimidazole in the caramel colouring used in their soft drinks, in order to avert placing a carcinogen warning label on their products, as part of California law. In 2011, 4-methylimidazole (CAS No. 822-36-6) was added to California’s Proposition 65 List (OEHHA, 2012), as a suspected cancer causing chemical. This action was undertaken as a result of carcinogenicity studies performed in rats and mice, by the National Toxicology Program (NTP) (NTP, 2007). The OEHHA reported a no significant risk level (NSRL) for 4-methylimidazole at 16 µg/day (this level of intake is the level that is calculated to result in no more than 1/100,000 excess cancer case, and assumed an exposure of the substance over a 70 year lifetime period) (OEHHA, 2011).

Earlier animal studies conducted on 4-methylimidizole have observed convulsions in rabbits, mice and chicks when administered orally, at doses of 360 mg/kg body weight (World Health Organization (WHO), 1975). Short term studies conducted on caramel colour did not result in abnormalities or significant adverse effects in rats and dogs at doses up to 20% or 25% in the diet, respectively (WHO, 1975).

In the NTP studies, rats and mice were given 4-methylimidazole in feed for 2 years at doses ranging from 0 – 2500 ppm or 0 – 1250 ppm, respectively. The study concluded no evidence for carcinogenicity for 4-methylimidazole in male rats; however, there was equivocal evidence for carcinogenicity in female rats due to an observed increase in the incidence of mononuclear cell leukemia. There was clear evidence of a carcinogenic effect in mice (male and female) by 4-methylimidazole, due to the increased incidences of alveolar and bronchiolar tumors. Furthermore, results from genetic toxicology studies conducted in in vitro and in vivo systems, were negative and indicate a lack of genotoxic and mutation effects of 4-methylimidazole.

In 2011, the advocacy group Center for Science in the Public Interest (CSPI) submitted a petition to the U.S. Food and Drug Administration to revoke the use of caramel colouring containing 4-methylimidazole and 2-methylimidazole (CSPI, 2011). The report summarized the carcinogenic effects observed in the NTP feed studies conducted in rats and mice, and outlined the potential increased risk in cancer to soft drink consumers. The CSPI noted an approximate exposure dose of 130 µg of 4-methylimidazole in a 12 ounce serving of cola, exceeding the NSRL established by the OEHHA (CSPI, 2011).

Although the NTP study data indicated clear carcinogenic effects in mice, Chan et al., (2008) published the results of the NTP studies, and additionally noted observations of an anti-carcinogenic effect in rats, as females had reduced incidences of reproductive organ tumors compared to the control group, and male rats had reduced incidences of tumors in the adrenal medulla and pituitary gland. The CSPI noted that the food industry has argued that the anti-carcinogenic activity seen in rats should not warrant a listing of 4-methylimidazole and subsequent warning label on foods that would contribute to ingestion of more than 16 µg of this substance per day (CSPI, 2011). However, other bodies have noted that this effect may have been attributed, at least partially, to a reduction in body weight (CSPI, 2011). Tumor preventive activity of 4-methylimidazole in the rat was further evaluated in a recent publication by Murray (2011), citing that the reduced body weight did not offer a full explanation for the reduced incidence of tumors in rats treated with 4-methylimidazole, thereby indicating a role for this substance in cancer prevention (Note: a conflict of interest was reported in the publication as funding was received from the American Beverage Association).

The American Beverage Association (2012) made a recent statement addressing the modifications to the caramel colour formulation used in beverages to meet California’s law. The group provided additional facts on the safety of caramel colouring, containing trace levels of 4-methylimidazole, and contended that more than 2900 cans of cola would have to be consumed daily to reach the lowest dose level of 4-methylimidazole tested in mice, in the NTP studies.

It will be interesting to witness the full impact, if any, of the 4-methylimidazole listing on California’s Proposition 65 on other government and regulatory bodies. Further research on carcinogenicity of 4-methylimidaznole is warranted in order to evaluate the true risk it may have in foods and food products.

dicentra will continue to bring you updates on substances of concern as more information becomes available.


American Beverage Association (2012). Beverage Industry Addresses Caramel Coloring And 4-MEI. News Releases & Statements. March 9, 2012. Available at: http://www.ameribev.org/news–media/news-releases–statements/more/269/

Centre for Science in the Public Interest (CSPI), 2011. Petition to Bar the Use of Caramel Colorings Product with Ammonia and Containing the Carcinogens 2-Methylimidazole and 4-Methylimidazole. Submitted to the U.S. Department of Health and Human Services Food and Drug Administration. February 16, 2011. Available at: http://cspinet.org/new/pdf/caramel_coloring_petition.pdf

Chan PC, Hill GD, Kissling GE, Nyska A. Toxicity and carcinogenicity studies of 4-methylimidazole in F344/N rats and B6C3F1 mice. Arch Toxicol. 2008 Jan;82(1):45-53. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2366200/pdf/nihms44466.pdf

Dills WL Jr. Protein fructosylation: fructose and the Maillard reaction. Am J Clin Nutr. 1993 Nov;58(5 Suppl):779S-787S. Available at: http://www.ajcn.org/content/58/5/779S.full.pdf

Murray FJ. Does 4-methylimidazole have tumor preventive activity in the rat? Food and Chemical Toxicology 49 (2011) 320–322.

NTP, 2007. Abstract for TR-535 – 4-Methylimidazole (CASRN 822-36-6). Toxicology and Carcinogenesis Studies of 4-Methylimidazole (CAS No. 822-36-6) in F344/N Rats and B6C3F1 Mice (Feed Studies). Available at: http://ntp.niehs.nih.gov/?objectid=9B956B07-F1F6-975E-79BBCDCCD57001C8

Office of Environmental Health Hazard Assessment (OEHHA), 2012. -Methylimidazole (4-MEI) A Fact Sheet. Available at: http://oehha.ca.gov/public_info/facts/4MEIfacts_021012.html

OEHHA, 2011. No Significant Risk Level (Nsrl) For The Proposition 65 Carcinogen 4-Methylimidazole. Reproductive and Cancer Hazard Assessment Branch, Office of Environmental Health Hazard Assessment (OEHHA) California Environmental Protection Agency. Available at: http://oehha.ca.gov/prop65/law/pdf_zip/010711NSRLrisk4EI.pdf

World Health Organization (WHO), 1975. Who Food Additives Series 6. Joint FAO/WHO Expert Committee on Food Additives. International Programme On Chemical Safety. Available at: http://www.inchem.org/documents/jecfa/jecmono/v06je13.htm

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