Drinking several cups of green tea each day may substantially reduce a person's risk of cardiovascular disease, a study of more than 40,000 people in Japan has found. But the new findings also cast doubt on the prevalent idea that the drink offers protection against cancer.
Controlling for lifestyle factors, those who consumed more than five cups of green tea daily had a 26% lower risk of dying from cardiovascular disease than those who consumed less than one cup per day.
Exactly how the tea protects against heart disease remains unclear, but Kuriyama speculates that antioxidant chemicals in green tea, called polyphenols, reduce the action of free radicals in the body, which may damage cells.
Milton Schiffenbauer of Pace University in New York, US, says that by protecting against this damage, polyphenols may reduce the blood vessel inflammation thought to promote cardiovascular disease.
The new study did not find evidence to support the idea that green tea consumption reduces the risk of cancer. The Japanese researchers found no significant difference in cancer-related mortality among the different groups.
Previous studies suggest the drink may protect against cancer of the prostate or lung. They have also isolated specific receptors on the surfaces of cancer cells that green tea compounds may interact with.
"It's been suggested time and time again that it does provide protection against cancer," says Schiffenbauer, whose previous work found evidence that black and green tea also deactivates viruses, including herpes.
He adds that although the new research from Japan found no link between tea consumption and cancer risk, more research is needed to resolve the conflict between this and previous cancer-related studies.
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