Experiments in Germany tested 22 flavonoids on human lung cells infected with the H5N1 influenza A virus.

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More studies are needed to decipher the pharmacological actions of flavonoids, they said.

WSJ: Sleep's Surprising Effects on Hunger

Although structurally similar, the flavonoids differed in their anti-influenza mechanisms, researchers said.

WSJ: Sleep's Surprising Effects on Hunger

The flavonoids inhibited the secretion of various inflammatory cells called cytokines in H5N1-infected cells, but had no effect on noninfected cells or tumor necrosis factor, a key inflammatory protein.

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Experts believe that natural compounds known as flavonoids (or flavonols), which appear to promote artery health and reduce inflammation, are responsible for the cardiovascular benefits that have been associated with chocolate consumption.

CNN: Daily chocolate may keep the heart doctor away

In separate experiments, the two flavonoids were added to lung-cell cultures before, during and after infection with H5N1, and tested on H5N1-infected cells treated with zanamivir (brand name Relenza), an antiviral drug prescribed to flu patients.

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Flavonoids and flu: Two plant-based flavonoids disease-fighting compounds found in many foods significantly impaired the infectious activity of H5N1 avian-flu virus in laboratory experiments and may form the basis of future influenza treatments, a report in Antiviral Research says.

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"The benefits of chocolate come from flavonoids, and those are mainly found in dark chocolate, not Easter eggs, which are usually milk chocolate and have a lot of saturated fat, " says Julia Zumpano, a registered clinical dietitian at the Cleveland Clinic, in Ohio.

CNN: Daily chocolate may keep the heart doctor away