Could green tea be key in the fight against cancer?
9 November 2009
Research in the US has added weight to the brewing body of evidence that green tea may help to prevent certain types of cancer.
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Dr Virgina Warren, assistant medical director for Bupa |
One of the great benefits of looking at natural preventative treatments like green tea is that it is cheap and readily available. However, to date, studies into the effect of green tea on cancer have produced conflicting results. 
The scientists studied 41 people with a pre-cancerous mouth condition called oral leukoplakia. Each person was randomly assigned to one of four groups - three groups took a green tea extract in tablet form, and the fourth group who took a dummy tablet (placebo). Those given the green tea extract took a dose of either 500mg/m, 750mg/m or 1,000mg/m, which had been specially prepared by the researchers.
At the start of the study each person was asked questions about their medical history and underwent several physical examinations and laboratory tests. This included having a biopsy (a small sample of tissue) taken of the pre-cancerous lesions in their mouth. They then carried out the same tests again 12 weeks after starting the treatment.
The scientists found that the groups who took the highest doses of green tea extract (750mg/m and 1,000 mg/m) had fewer abnormal cell changes in their mouth than those who took the low dose or dummy tablet, thus delaying or preventing the development of mouth cancer. The researchers believe that green tea extract helps to block blood vessel growth in pre-cancerous cells in the mouth so that a tumour can't develop.
However, none of the findings were statistically significant, which means that the scientists couldn't rule out that the effects seen were purely down to chance. This is most likely to have been a result of the small number of people used in the study.
Dr Virgina Warren, assistant medical director for Bupa, commented: "One of the great benefits of looking at natural preventative treatments like green tea is that it is cheap and readily available. However, to date, studies into the effect of green tea on cancer have produced conflicting results. This pilot study does appear to suggest that green tea may help to prevent mouth cancer if you have oral leukoplakia, but the results weren't statistically significant and certainly shouldn't be applied to other types of cancers. I'd advise caution until larger, more robust randomised studies have been completed in humans.
"If you're thinking of upping the amount of green tea you drink as a result of this or other studies, it's wise to remember that green tea does contain caffeine. The people taking the highest doses of green tea in this study had the equivalent of eight cups a day, and they did have some caffeine-related side-effects, such as nausea and insomnia. Drinking three to five cups of green tea a day is generally considered safe, but if you're pregnant, high doses of caffeine are not advisable as they can affect your baby's growth and development."
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Related information
Read the study
Tsao AS, Liu D, Martin J, et al. Phase II randomized, placebo-controlled trial of green tea extract in patients with high-risk oral premalignant lesions. Cancer Prev Res 2009; 2(11):931-41. doi:10.1158/1940-6207
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