OREGON STATE UNIVERSITY

Health issues uncertain as tea sales boom

10/18/2005

CORVALLIS, Ore. - Sales of bottled tea products are increasing rapidly as some manufacturers tout the possible health benefits of antioxidants and polyphenols found in these beverages, but researchers at Oregon State University say tea marketing may have gotten ahead of the science - and consumers should learn more about the facts.

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.

However, the real health value of drinking tea is uncertain and far more complex than often understood. And the bottled teas that appear to be riding a current wave of popularity also have far lower levels of the antioxidants and other compounds 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 in OSU's Linus Pauling Institute and a world leader in the study of the health value of tea.

"However, the epidemiological and demographic evidence of cancer prevention in humans is far less clear and the studies are somewhat conflicting," said Dashwood, who heads LPI's Cancer Chemoprevention Program, has served on federal panels of the National Institute of Environmental Health Sciences that analyze carcinogens, and has research funded by the National Institutes of Health.

"In the end, we may be able to show the value of tea consumption in combination with a healthy lifestyle, especially in the prevention of cancers of the gastrointestinal tract," Dashwood said. "But the benefits are not that simple or obvious, and may not be as profound as some advertising campaigns would have you believe."

A particular concern, he said, is the bottled products that are increasing in popularity.

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. "And it also appears that the antioxidant or polyphenol activity found in some of them may be due in large part to the fruit additives used as flavorings, and have little to do with the tea polyphenols."

Among the findings in recent studies that relate to the health value of tea:

  • White tea appears to have more anti-mutagenic 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.
  • White tea does not necessarily have more antioxidants than green tea, it varies greatly with the brand and tea cultivar.
  • Antioxidants in tea are poorly absorbed by the body, and some of the polyphenol compounds, which are also found at high levels in black tea, may be the key to any cancer prevention.
  • Epidemiologic studies done in places where tea consumption is comparatively high fail to show any consistent overall reduction in cancer incidence.
  • Some of the human data indicates protection against gastrointestinal cancers, and possibly prostate cancer, but black tea may work just as well as white or green teas.
  • Some of the protective compounds in tea can be quite unstable and degrade quickly with time, and the levels in bottled teas often decline markedly from those in freshly brewed tea.

    "There's just a lot we still don't know about the health benefits of tea consumption," Dashwood said. "There's some evidence that it may help protect humans against some cancers. But it may make a difference what tea you drink, how you prepare it, when you drink it, what you mix with it, and what cancers it will have any effect on. I know this is frustrating for people who want more simple answers, but we just don't have them yet."

    One thing is pretty clear, Dashwood said. Drinking tea may complement a healthy lifestyle, but it will not make up for the lack of one. A balanced diet with large amounts of fruits and vegetables, a proper body weight and regular exercise are still of primary importance, he said. And consumption of brewed tea products appears to have more cancer prevention value than any type of supplement.

    OSU laboratories are one of the world leaders in the study of white tea, which has recently been hailed by some as "the new green tea" because of its alleged superiority in health value. But in practice there is not that much difference between green and white teas, Dashwood said, and there is no human epidemiology data to support the case that white teas are more beneficial than green or black teas.

    The distinction between these products is largely one of processing, because all are made from the same basic plant, Camellia sinensis. White tea is the least processed, with a lot of buds, and has a subtle, slightly sweet flavor. Continued processing produces green, oolong and eventually black tea.

    Regardless of the findings, the public curiosity about tea continues to be huge.

    The Linus Pauling Institute web site at http://lpi.oregonstate.edu contains a micronutrient information center for consumers and a wealth of information about other issues, including the life and career of Linus Pauling, a two-time Nobel laureate and OSU alumnus.

    Only one topic draws as much interest as information about Pauling - inquiries about white tea.