Drink giants Coca Cola and Pepsi have altered their recipes in order to avoid having to display cancer warnings on their products, they announced on Thursday.

The new recipe for the caramel colouring used in the drinks has been changed to comply with California laws. The state has added 4-methylimidazole (4-MI), an ingredient used in the fizzy drinks recipes, to its list of carcinogens.

The manufacturing process will be modified in order to reduce the levels of 4-MI which can formed during the cooking process.

"While we believe that there is no public health risk that justifies any such change, we did ask our caramel suppliers to take this step so that our products would not be subject to the requirement of a scientifically unfounded warning," Coca-Cola representative Diana Garza-Ciarlante told the Associated Press news agency.

The change, which has already been introduced in California, will now be rolled out across the US as manufacturers claim the alteration makes the drinks more efficient to manufacture.

The drinks have been linked to cancer in mice and rats but an individual would need to drink 1,000 cans of Coke or Pepsi to take in the same dose of the chemical given to animals in the lab tests, according to the US Food and Drug Administration.

The American Beverage Association (ABA), which represents the drinks industry, said its member companies would continue to use caramel colouring in their products but alterations were being made to adhere to Californian standards.

"Consumers will notice no difference in our products and have no reason at all for any health concerns," the association said in a statement.

California's Office of Environmental Health Hazard Assessment requite any produced containing a level of 29 micrograms of 4-MI had to bear a cancer warning label. According to a study by the Centre for Science in the Public Interest (CSPI) the soft drink cans contained levels nearing 140 micrograms in each 12-ounce can.

But the ABA scoffed at the research, saying it was nothing more than CSPI scare tactics.

"In fact, finds of regulatory agencies worldwide ... consider caramel colouring safe for use in foods and beverages," it said.

According to Beverage Digest, Coca Cola and Pepsi account for nearly 90% of the fizzy drinks market.