The chemical process during the manufacture of the caramel coloring used in soft drinks such as cola produces a carcinogen that could be raising the risk of cancer to above the accepted threshold of one extra case in every 100,000 people consuming the drinks, suggests an analysis.

Share on Pinterest The coloring is not necessary for the production of soft drinks and is included purely for esthetics.

Matching laboratory tests conducted by Consumer Reports on 11 different soft drinks, first reported last year, with an analysis of average consumption by Americans, the researchers found that one can a day could be enough to expose them to potentially cancer-causing levels of the chemical known as 4-MEI (short for 4-methylimidazole).

The potential carcinogen is formed during the manufacture of the familiar caramel color that is added to many widely-consumed beverages.

A law in California requires that drinks must carry warning labels if they contain enough 4-MEI to pose an excess cancer risk of more than 1 case in every 100,000 exposed people (an exposure of 29 mcg of 4-MEI every day).

Testing on 110 samples of soda brands carried out by the Consumer Reports researchers, led by a team at the Johns Hopkins Center for a Livable Future in Baltimore, MD, found that drinks contained levels ranging from 9.5 mcg per liter (mcg/L) to 963 mcg/L.

Concentrations of 4-MEI varied considerably by soda brand and state of purchase, the researchers concluded, “but were generally consistent across lots of the same beverage purchased in the same state/area.”

They add: “Routine consumption of certain beverages can result in 4-MEI exposures greater than 29 mcg a day” – the level that triggers a new case of cancer in every 100,000 people consuming the drink, toxicity that was established by previous studies in mice and rats conducted by the US National Toxicology Program.

The researchers say there was not enough data from individual drinks samples to recommend one brand over another in terms of carcinogen exposure, but suggest: “State regulatory standards appear to have been effective in reducing exposure to carcinogens in some beverages.”

Lead author of the study Tyler Smith, a program officer with the Johns Hopkins Center for a Livable Future, says 4-MEI levels can “vary substantially across samples, even for the same type of beverage.” Smith explains:

“For example, for diet colas, certain samples had higher or more variable levels of the compound, while other samples had very low concentrations.”

In the lab sampling, Malta Goya had the highest 4-MEI concentration while Coca-Cola produced the lowest value.

California listed 4-MEI as a carcinogen in 2011, under the Safe Drinking Water and Toxic Enforcement Act of 1986 – better known as Proposition 65. The authors say their results suggest that “federal regulation of 4-MEI in caramel color may be appropriate.”