March 5, 2012 -- Lab tests commissioned by a consumer group find that popular colas -- including Coke and Pepsi -- carry a caramel-coloring chemical that causes cancer in lab animals.

The chemical, 4-methylimidazole or 4-MI, comes from the sodas' caramel coloring. That color is made not from natural caramel but via a chemical process involving ammonia.

While toxicology studies show that 4-MI can cause cancer in lab animals, it's not clear whether it's a human carcinogen -- or whether the amounts detected in sodas pose any kind of a threat.

The Center for Science in the Public Interest (CSPI) in February 2011 petitioned the FDA to ban this kind of caramel coloring. It also wanted the cosmetic additive renamed "chemically modified caramel coloring" or "ammonia-sulfite process caramel coloring."

"Coke and Pepsi, with the acquiescence of the FDA, are needlessly exposing millions of Americans to a chemical that causes cancer," CSPI Executive Director Michael F. Jacobson says in a news release.

The CSPI-commissioned tests detected 4-MI in regular and diet Coca-Cola and Pepsi products -- in millionths of a gram per 12-ounce can. CSPI notes that these quantities are several times higher than a controversial benchmark set by the state of California's Office of Environmental Health Hazard Assessment.

The major supplier of caramel coloring to the beverage industry already has altered the chemical process used to make the product. The reformulated product will comply with the California benchmark, even though the company strongly disagrees with the California assessment. The new product will be used throughout the U.S.

In an email to WebMD, the FDA says it "is working with manufacturers to determine the actual usage of these caramel colors and the amount of 4-MI found in colas and other food products."

While the CSPI suggests that 4-MI is causing cancer in thousands of Americans who drink a lot of cola, the FDA says few people should worry.

"A consumer would have to consume well over a thousand cans of soda a day to reach the doses administered in the studies that have shown links to cancer in rodents," the FDA tells WebMD.

And while it believes 4-MI is a threat, the CSPI says it's less of a threat than the obesity-promoting high-fructose corn syrup in soft drinks.

In response to the 2011 CSPI petition, the Coca-Cola Company said, "CSPI’s statement irresponsibly insinuates that the caramel used in our beverages is unsafe and maliciously raises cancer concerns among consumers. This does a disservice to the very public for which CSPI purports to serve. In fact, studies show that the caramel we use does not cause cancer."

In response to the new CSPI findings, the American Beverage Association says, "This is nothing more than CSPI scare tactics, and their claims are outrageous. The science simply does not show that [4-MI] in foods or beverages is a threat to human health."