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GREEN (AND, TO A LESSER EXTENT, BLACK) TEA - MAGICAL POTIONS OR HYPE - OR A LITTLE OF BOTH
(July 2004)

Green tea is on a roll. At a meeting of the American Association for Cancer Research in November 2003, investigators trumpeted its ability to reduce cancer-producing damage to cells caused by cigarettes and to prevent liver cancer. Other studies suggested green tea could be used to treat several types of cancer. And, an as yet unpublished study from China found that tea drinkers had one-third the risk of prostate cancer as non-tea drinkers. At about the same time, an article appeared in a less well-known medical journal by a well-respected researcher titled “Regular intake of tea can decrease the risk of heart disease and several types of cancer and provides the basis for improved aging”. The breadth of the claims was extraordinary - black and green teas reduce the risk of heart disease and certain cancers (especially of the esophagus), improve metabolism by getting rid of less desirable organisms in the intestinal tract, facilitate healthy aging, allow people to live longer, and help in weight control.

Teas contain lots of phenols that could indeed have health-promoting qualities, but there are lots of problems with the claims:

- The studies on heart disease and stroke prevention are quite inconsistent. Most of these relate to black tea. The author refers to a meta analysis in which all the relevant studies were combined and an 11 percent reduced occurrence of “heart disease” was found. But, examination of that study paints a somewhat different picture. The authors said they could not make any judgement about coronary heart disease; the 11 percent reduction found with an increase of three cups of tea a day was not statistically significant, and the authors noted that “evidence of a bias towards preferential publication of smaller studies that suggest protective effect urges caution on interpreting this result”. In regard to stroke, they said no judgement could be made; of six studies they cited, two showed significant reduction in stroke, three were not statistically significant, and one showed increased risk. That is hardly strong evidence for reduction in risk of heart attack or stroke.

The other article quoted in regard to heart disease is about green tea. According to Japanese investigators, ten cups or more a day reduced cardiovascular disease by 42 percent in men, but non-significantly in women. That is a lot of tea.

The article then says green tea lowered the risk of esophagus cancer in China, but a review of the original article indicates no significant reduction in men, and the significant findings in women were based on very few cases.

The statements made dogmatically, that tea changes the bacteria in the intestines and thereby improves metabolism, that it helps prevent overweight, and that it modifies aging so people can live longer are not supported by evidence in humans.

So, this article, even though written by a distinguished scientist, is a mixture of interesting experimental studies and hyperbole about human benefits.

Green tea does seem to have health-promoting possibilities especially in regard to cancer, but despite the enthusiastic reports cited at the beginning of this editorial, there are lots of inconsistencies. For example, one of the cancers that supposedly is prevented by green tea is stomach cancer. Several Chinese and Japanese studies claim protection, but the best designed study is from Japan and shows no benefit from either green or black tea.

Tea, especially green tea, may be on a roll, but it is well to remember that the early reports tend to be positive, and only later do the negative reports appear. Green tea has potent antioxidants and may also act beneficially by other mechanisms, including effects on genes. Green (and black) teas are likely not harmful and they may promote health (reduced risk of heart disease, some cancers, osteoporosis);

BUT,

at present, no claim is adequately documented. Will claims of prevention benefits for green tea go the way of vitamin C for heart disease and cancer, vitamin E for heart disease, beta carotene for heart disease and cancer and be found to be ineffective? Or will green (and maybe black) teas turn out to be marvelously health promoting-disease preventing? Or will the final judgement be in the middle - some benefit, but nothing extraordinary? Only time and many more studies will tell - and, if there is benefit, we will have to sort out the dosage (how many cups a day are needed).

But, there is no doubt that teas, especially green tea, are of great interest and deserve a lot of scientific attention.

Weisberger, J.H. Regular intake of tea can decrease the risk of heart disease and several types of cancer and provides basis for improved aging. The Original Internist. Vol 10 (September) Pgs 25-29. 2003.