The Center for Science in the Public Interest has asked US authorities to ban certain caramel colourings believed to be used widely in colas, because they have been linked to cancer.

Caramel colourings 2-methylimidazole and 4 methylimidazole (2-MI and 4-MI) have been linked to increased cancer risk in Government-funded studies on mice and rats, the Center for Science in the Public Interest (CSPI) said today (17 February).

It has filed a petition with the US Food & Drug Administration, asking the safety watchdog to ban the colourings from use in food and soft drinks, such as colas. It said that researchers at the University of California, Davis, found significant levels of 4-MI in five brands of cola.  

The CSPI said that state health officials in California have added 4-MI to the state’s list of “chemicals known to the state to cause cancer”. The risk is related to caramel colourings produced from ammonia, said the CSPI, which has found five toxicology specialists to back its argument, including two who work for US Department of Health and Human Services.

"The FDA should act quickly to revoke its approval of caramel colorings made with ammonia," said the CSPI.

To read an update to this story, including reaction from the soft drinks industry, click here.