CORVALLIS, Ore. - Bottled tea sales are increasing as the possible health benefits are being promoted, but researchers say it is too early to say whether the beverage really does offer any significant protection against diseases such as cancer.
One industry survey indicates that sales of ready-to-drink tea grew 10 percent in the first half of 2005, and the sales volume of one large manufacturer has been reported to be 35 percent higher.
But Oregon State University researchers say the real health value of drinking tea is uncertain while some popular bottled teas have far lower levels of the antioxidants and other compounds such as polyphenols that may provide protection against cancer.
"It's true that freshly brewed tea does have significant levels of antioxidants and polyphenols, and the evidence in animal tests of cancer prevention is actually quite compelling," said Rod Dashwood, a professor at OSU's Linus Pauling Institute.
"But the benefits are not that simple or obvious, and may not be as profound as some advertising campaigns would have you believe," Dashwood said.
Studies on the benefits are conflicting, said Dashwood, who heads the institute's cancer chemoprevention program and has served on federal science panels.
In addition, some of the bottled tea products studied by OSU researchers have levels of polyphenols and antioxidant activity 10 to 100 times lower than conventionally brewed tea, regardless of whether they are based on green teas or the white teas that supposedly have more health value.
"Many of the currently available cold bottled teas sold in the U.S. are more like diluted sugar water than something that will help protect your health," Dashwood said.
Among the findings in recent studies that relate to the health value of tea:
- White tea appears to have more cancer-preventing activity in laboratory tests than green tea. But animal tests show both green and white teas have similar value in tumor inhibition and blocking the development of pre-cancerous lesions.
- Antioxidants in tea are poorly absorbed by the body.
- Studies done in places where tea consumption is comparatively high fail to show any consistent overall reduction in cancer incidence.
- Black tea may work just as well as white or green teas.
"There's just a lot we still don't know about the health benefits of tea consumption," Dashwood said.
But one thing is clear, he said. Drinking tea may complement a healthy lifestyle, but it will not make up for the lack of a balanced diet with large amounts of fruits and vegetables, proper body weight and regular exercise, Dashwood said.