Solid evidence is mounting that drinking tea can prevent cell damage that leads to cancer, heart disease and perhaps other ills, scientists said on Tuesday.
It may soon be time to add tea to the list of fruits and vegetables that experts urge Americans to eat as often as possible to reduce their risk of disease, the researchers told a meeting sponsored by the US Department of Agriculture, the Tea Council, the American Cancer Society and other groups.
"In some respects, it is good to think of it as a plant food," Jeffrey Blumberg, a nutritionist at Tufts University in Boston, told a news conference.
Blumberg said tea is loaded with phytochemicals - a wide range of molecules that can act as antioxidants. Such compounds counteract the damage done to DNA cells by free radicals - charged particles produced by sunlight, chemicals, many foods and simply the stress of day-to-day living.
Damaged DNA is the first step to cancer, and is also associated with heart disease.
Vitamins such as A and C are antioxidants, but so are compounds such as the catechins found in tea.
"It's taken about 30 years to fully appreciate the importance of these compounds," said Blumberg, who acts as an adviser to both the US Food and Drug Administration and the Tea Council.
The USDA reported on a study suggesting that tea-drinking can also reduce the risk of heart disease by lowering cholesterol.
Joseph Judd, acting director of the USDA's Beltsville Human Nutrition Research Center in Maryland, tested eight men and eight women who agreed, for a period of three weeks at a time, to eat and drink only what they were given at the Beltsville lab.
"We gave them a beverage that mimicked tea - water flavoured like tea," he said. For a second three-week period the same volunteers got five cups a day of tea to drink.
"We found that their blood lipids, when they drank tea compared to the placebo beverage, had up to 10 per cent lowering of low density lipoprotein, the 'bad' cholesterol," Judd said.
Overall, total cholesterol was lowered 6 per cent on average over the three weeks, his team found. "There was no effect on 'good' cholesterol," he added. "HDL remained constant."
Dr Iman Hakim of the University of Arizona and the Arizona Cancer Center tested 140 smokers to see if drinking tea could affect levels of chemicals associated with DNA damage.
They chose to look at a chemical called 8-OhDG, which is found in urine and linked to the damage of DNA in the cells.
"They were asked to eat whatever they were eating and just add tea to their diet," she said.
For four months, volunteers drank either green tea, black tea or water. Hakim's team tested their urine for levels of 8-OHdG. "What we found was a 25 per cent decrease in the green tea group," she said.
No changes were seen in the people who drank black tea or water. "We think green tea, in our group of smokers, is associated with a reduction of oxidative stress in their urine," Hakim said.
Much more research would be needed to see if lowering levels of 8-OhDG, or other markers of DNA damage, is actually associated with a lower risk of cancer.