A new study has found that chlorophyll in green vegetables reduces tumors up to a point, but high exposure to cancer causing agents can have just the reverse effect.

Chlorophyll, a pigment that helps plants obtain energy from light for the purpose of photosynthesis, has been long discussed as an anti-cancer agent. But as they are found in very low levels in edible plants, it seldom suffices for protection. It is often used as a food dye, a wound-healing accelerant, and for odor control.

For the study, researchers at the Oregon State University used 12,360 rainbow trout fishes as laboratory models instead of rodents where chances of carcinogen exposure are much higher.

"This study, like others before it, found that chlorophyll can reduce tumors, up to a point...But at very high doses of the same carcinogen, chlorophyll actually made the problem worse," said Tammie McQuistan, a research assistant working with George Bailey, a professor emeritus in the Linus Pauling Institute at the OSU.

Their earlier studies found positive results with chlorophyll in both mice and trout.

The finding, however, questions traditional research methods that rely on more expensive rodent studies done under high toxic exposures and the role of dietary or pharmaceutical approaches in studying cancer-causing compounds.

The study found that chlorophyll administration under the exposure of fairly moderate levels of a known carcinogen reduced the number of liver tumors in trout by 29-64 percent, and stomach tumors by 24-45 percent.

But in another part of the study, that used much higher and unrealistic doses of the same carcinogen, the use of chlorophyll caused a significant increase in the number of tumors.

Thus, traditional research methods that use lesser number of animals but high doses of carcinogen might conclude that chlorophyll increases the risk of cancer but this study clearly indicates that at lower yet relevant carcinogen doses, chlorophyll is actually strongly protective.

It binds with the carcinogen within the gastrointestinal tract and isolates them until they are eliminated from the body.

Researchers found that the carcinogen dose-dependently changed gene expression in the fish that were fixed by the chlorophyll, reduced tumor multiplicity and incidence that had risen due to carcinogenic exposure. But there were no changes when chlorophyll was given without the carcinogen.

"The central assumption of such experiments is that intervention effects at high carcinogen dose will apply equally at lower carcinogen doses," the researchers wrote in their report. "Contrary to the usual

assumption, the outcomes in the major target organ were strikingly dependent on carcinogen dose," the study authors wrote.

The article was published in the journal Food and Chemical Toxicology.

Studies have already shown that people who eat more natural plant foods-vegetables, fruits, legumes-are less likely to be diagnosed with cancer.

Currently, Chinese researchers are studying the long term effect of chlorophyllin in treating liver cancer in a clinical trial spanning 20 years. Chlorophyllin is a derivative of chlorophyll in which the magnesium in its center is removed and replaced with copper.