The Soda-Cancer Connection

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Drinking Diet Coke, Dr. Pepper, or any dark-colored soda may raise your cancer risk, according to a new report from Johns Hopkins. This new analysis follows up a study done by the same researchers last year for which they purchased 110 cans of soda from stores in New York and California and tested them all for 4-MEI. They detected a huge range in 4-MEI levels, from 3.4 micrograms up to 352.5 micrograms per 12-ounce can.

What do those numbers mean in terms of cancer risk? While the federal government has not set a limit for how much 4-MEI may be carcinogenic, the state of California has. Under California law, a product is required to carry a cancer warning if it exposes consumers to 29 micrograms of 4-MEI. So, given that the Johns Hopkins team found levels up to 352.5 micrograms in some sodas, you can see why this is a potentially dangerous health problem.

But here's the really interesting part: According to lead researcher Keeve Nachman, the sodas bought in California tended to have markedly lower levels of 4-MEI than those purchased in New York, where there is no law limiting 4-MEI. His team even saw this trend when comparing cans of the exact same brand and product purchased in the two different states. "It appears that soda manufacturers are using a different type of caramel color that has less 4-MEI in the beverages they sell in California," Nachman says.

The issue for consumers is that even though there are different types of caramel color — some of which do not contain 4-MEI — there is no way of knowing what kind is being used in a beverage or food product. Unlike in Europe, where the particular type of caramel color must be specified on a label, U.S. manufacturers are only required to list "caramel color."

"The real issue with this ingredient is its 'often unknown' composition,"  says Kantha Shelke, a food scientist and principal at food science and research firm Corvus Blue. "The large amount of caramel color that's consumed is also problematic, since it is the single-most widely used food coloring in the world. But I'd say the biggest issue for consumers is the lack of transparency around it."

Unfortunately, assessing the actual darkness of a soda won't even tell you which type of caramel color was used. "Dark color is not a dead ringer for high levels of 4-MEI," Nachman says. Some very dark drinks his team tested had low levels, while lighter-hued beverages had higher amounts.

It should be noted that the potential cancer risks associated with 4-MEI have been learned through animal studies, not human trials. "The effects of 4-MEI have never been studied in humans, because chemicals are not tested on people," Nachman says. "So although we don't know for absolute certain that 4-MEI poses a risk, we can't interpret that to mean that there is no risk." What researchers do have, Nachman explains, is an animal study published by the National Toxicology Program in 2007 that found that 4-MEI caused lung tumors in mice. "California looked at the NTP's evidence and decided to regulate 4-MEI because of it," he says. "In my eyes, it makes the most sense for the federal government to cap 4-MEI limits so consumers are not required to assess risk."