CancerCochrane LibraryProf. ErnstTea

Does green tea prevent cancer?

 Based on studies of more than a million people, Prof. Ernst and colleagues concluded, “Drinking green tea remains unproven in cancer prevention.”

First, the details.

  • 51 studies of more than 1.6 million participants were reviewed.
  • 47 studies were carried out in Asia where the tea drinking culture is pronounced.
    • 27 were case-control studies: people with a specified condition (the cases) and persons without the condition (controls) are compared for characteristics or exposures that might contribute to or prevent the condition.
    • 23 were cohort studies: people with some common feature (eg, age, geography) are identified and studied over time to learn about differing health and illness experiences.
    • 1 was a randomized controlled trial: designed to show a cause and effect relationship by measuring how a change in 1 factor influences a second factor.
  • 27 studies tried to establish an association between green tea consumption and cancer of the digestive tract — mainly the upper gastrointestinal tract.
  • 5 tried to show an association with breast cancer, 5 with prostate cancer, 3 with lung cancer, 2 with ovarian cancer, 2 with urinary bladder cancer, 1 with oral cancer, 3 other studies included patients with various cancers.
  • Most study protocols were of high to medium quality.

And, the results.

  • Results from studies of the risk of digestive tract cancer were contradictory.
  • Limited evidence supported a lower risk of liver cancer.
  • Evidence for esophageal, gastric, colon, rectum, and pancreatic cancer was conflicting.
  • In prostate cancer, the results suggested a decreased risk in men consuming higher quantities green tea or green tea extracts.
  • There was some evidence that green tea reduced the risk of lung cancer (especially in men).
  • Some studies suggested green tea might increase the risk of urinary bladder cancer, while others reported a decreased risk.
  • Green tea doesn’t decrease the risk of dying from gastric cancer.

The bottom line?
The authors concluded, “There is insufficient and conflicting evidence to give any firm recommendations regarding green tea consumption for cancer prevention.”

However, “drinking green tea appears to be safe at moderate, regular and habitual use.” The “desirable green tea intake is 3 to 5 cups per day (up to 1200 mL/day), providing a minimum of 250 mg/day catechins.”

7/14/09 13:09 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.