SAN DIEGO, Calif. - Some of the synthetic food dyes that are common in the American diet may actually help prevent cancer, according to a new study by researchers in the Linus Pauling Institute at Oregon State University.

The findings, revealed this week at the annual meeting in San Diego of the American Association for Cancer Research, run contrary to decades of suspicion about the safety of food dyes, and could open the door to new ways to protect against cancer through selective use of appropriate dyes.

Scientists say that blue peanut butter is one option that comes to mind.

In particular, the study found that two very commonly used dyes - blue number two, and red number 40 - offer a level of cancer protection in animal studies about equal to chlorophyllin. Chlorophyllin is a compound that has been shown to decrease levels of aflatoxin-induced DNA damage in humans that have been exposed to high levels of this cancer-causing agent.

Some other food dyes used in the past, both natural and synthetic, have been suspected to cause cancer or other health concerns. "We're not suggesting that people should rush out and buy a lot of candy or soft drinks that are colored with synthetic dyes, because those foods are usually high in sugar and limited in nutrients," said Gayle Orner, an assistant professor with the Linus Pauling Institute. "But this is clearly something that demands more study and could provide new options for cancer prevention."

OSU scientists were first intrigued by the potential value of certain food dyes because they appeared to have a chemical structure similar to other compounds that help mitigate the damage from carcinogens by forming a chemical complex with them.

Researchers examined the effect of selected dyes in years of study with rainbow trout, which are a proven model for cancer research. After exposure to aflatoxin, the trout that received either blue dye number two or red dye number 40 had a much lower incidence of liver tumors. Red dye number 40 also offered protection against dibenzopyrene, a potent carcinogen that can be found in cigarette smoke.

Their effectiveness against aflatoxin is of particular interest, Orner said, because it is a major cause of cancer in some countries and, as a natural compound, is still present at very low levels in peanut butter. With further study, she said, it might be possible to use dyes in the preparation of peanut butter - color it blue - and reduce the risk of exposure to aflatoxin.

"There may be a range of carcinogens with which food dyes could have some value, we're just beginning these studies," Orner said. "Of some interest is that these synthetic dyes could help protect us against the damaging compounds found in some natural foods, which is not ordinarily the way we look at things."

Food dyes have been used since ancient times, and the first synthetic dyes were used in the United States in 1886. There was very little regulation prior to 1904, and many of the 80 or more dyes used at that time were toxic. Some of the "natural" dyes used then were made from mineral pigments contaminated with lead, mercury, or arsenic.

This research evolved from years of studies conducted by OSU toxicologist George Bailey, an international expert on cancer chemoprevention, as well as contributions from OSU researchers Ulrich Harttig, Michael Simonich, and Jerry Hendricks.

The studies were supported by OSU's Marine and Freshwater Biomedical Sciences Center, which in turn is funded by the National Institute of Environmental Health Sciences.

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Gayle Orner,