(ScienceNews) - Modified forms of the red wine compound resveratrol slip into human tissue and can help kill cancer cells, according to a study in the Oct. 2 Science Translational Medicine. The finding may explain why the unmodified form of resveratrol, which in lab experiments shows anticancer properties, has yet to translate into health benefits for humans.

When 60 volunteers ingested at least half a gram of resveratrol a day, their bodies quickly created metabolized forms, researchers led by Karen Brown of the University of Leicester in England report. Although produced only in small amounts, resveratrol sulfates were the most common metabolites present in blood and intestinal tissue samples.

The researchers think that proteins in cell membranes usher resveratrol sulfates into cells. In mouse experiments the researchers found that once inside cells, the sulfate metabolites transform back to resveratrol, uncorking the chemical’s anticancer activities.

Finally, the team tested the sulfate form in human cells. The regenerated resveratrol killed cancerous cells but proved harmless to normal cells.