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This is the VOA Special English Health Report.

For many years, researchers have been studying ways to extend life and to improve health as people get older.

They know that laboratory rats and other creatures live longer if they are fed a diet with fewer calories than normal. Scientists have found that enzymes called sirtuins (sir-TOO-ins) help cells repair damage and survive longer.

David Sinclair of Harvard University calls sirtuins "guardians of the cell." Mister Sinclair has been looking for ways to strengthen this protection. He and his research team mixed some of the sirtuins with different molecules to test the effects. The molecule that reacted the most was resveratrol.

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Researchers at Harvard Medical School in Massachusetts say this natural chemical lengthened the life of yeast cells. The researchers reported their findings this month in the publication Nature.

One of the places resveratrol is found is in the skin of grapes. So, it is in wine. Red wine contains more of it than white wine.

The Harvard researchers placed different amounts of resveretrol into dishes of yeast. They discovered that the smallest amount of the chemical appeared to have the greatest effect. They found that the yeast cells divided seventy percent more than normal.

The researchers also exposed human cells to dangerous radiation. They found that the cells treated with resveratrol lived longer than those not treated.

Tests have also been done on fruit flies and worms. The researchers say the chemical appears to have a similar effect. Fruit flies and worms have a lot in common with human biology. Studies are also planned on mice and monkeys.

The researchers say they would like to extend human life by several years. They also want to make those last years of life healthier than they are now.

Mister Sinclair says he drinks a glass of red wine a day. Studies have shown that wine can be good for the heart. But the scientist adds that the resveratrol is lost in the air within a day of opening a wine bottle. Also, large amounts of alcohol can cause liver damage, weight gain and other problems.

Some experts like the idea of a drug that would copy the effects of a reduced-calorie diet as a way to extend life. But any drugs based on resveratol are years away.

This VOA Special English Health Report was written by Nancy Steinbach.