Cancer Decisions - WELLBEING Free Newsletter

IN THE MAILBAG

[There will be no newsletter this week as Dr. Moss is traveling. Our regular newsletter service will resume next week.]

Last week's article on the Japanese study demonstrating the health benefits of drinking green tea generated an interesting mailbag.

One reader had some useful observations on the issue of how the tea is prepared:

"The green tea study was Japanese but the tea recommendations and preparation information were not. This could make a difference. I do know that the daily green tea in Japan is different from gunpowder, but don't know if there are chemical or health promoting differences. Japanese tea is almost always prepared by putting tea loosely in the pot and pouring hot water over it. A biochemist that I met at an herb conference told me that regular green tea needed to brew for 4-5 minutes to meet antioxidant claims. He said that decaf produced a different chemical picture and not as many antioxidants. I am not sure if there is more recent research. At any rate the tea that is used in Japan is not decaffeinated."

Our correspondent is of course correct in pointing out that different preparation techniques and different varieties of tea may alter the quality and the nutritional composition of the resulting beverage. The Ohsaki study, to which our newsletter referred, was a population-based study that followed more than 40,000 individuals over a period of eleven years. By enrolling such a large number of participants, researchers were able to minimize the statistically confounding effect of different tea varieties and brewing techniques. In this study, no effort was made to investigate or standardize the type of green tea taken by the participants. Furthermore, measures of tea consumption were made on the basis of retrospective self-reports - that is, participants gave assessments of how much tea they typically drank. But because the study was what statisticians call "adequately powered" - that is, because it monitored a very large number of participants over a long period - it was nevertheless possible to draw useful conclusions from the data, even though there were a number of variables at work.

Another reader wrote asking about the nutritional value of green tea extract, and whether taking an extract would confer the same health benefits as drinking green tea itself.

No one has yet carried out studies in order to establish the relative merits of green tea extracts as compared to drinking brewed tea, but as a general rule it can safely be said that the natural foodstuff (in this case, the drink, freshly prepared) is usually of more direct nutritional benefit than an extract or supplement. Isolating and purifying the individual nutritional components of any foodstuff very often eliminates many important associated nutrients and co-factors, and this may profoundly affect the biological worth of the resulting extract.

That being said, however, there are circumstances under which it can be advisable to take green tea extract rather than drinking the tea itself. For example, patients who are taking anticoagulants to prevent blood clotting should avoid drinking significant quantities of green tea, as the relatively high concentration of vitamin K present in the beverage is capable of counteracting the effect of the anticoagulants and may precipitate a clotting episode.

And then there is the vexing question of fluoride. Several readers wrote to us, reminding us that all tea contains significant quantities of fluoride, and that by drinking several cups of green tea per day, one runs the risk of unwittingly increasing one's fluoride intake, with potentially detrimental results.

This is a legitimate concern. All tea bushes accumulate fluoride - and also, incidentally, significant quantities of aluminum - in their leaves, and infusing the leaves to make the familiar beverage does result in the release of fluoride.

In general, the older the leaf, the higher its fluoride concentration. Thus, so-called 'brick' teas (known as 'fu-brick' and 'black brick' tea), which are largely made from old and fallen leaves, are the most contaminated, and result in the most fluoride and aluminum rich infusions. By contrast, most good quality teas, including white and green teas, are made from only the buds and first tender leaf-pairs beneath the bud. These leaves contain considerably less fluoride and aluminum.

In an extremely interesting study carried out at the School of Life Sciences, Zhongshan University, Guangzhou, China, researchers set out to quantify the fluoride ingestion risk incurred by habitual tea-drinkers. They analyzed the fluoride content of a number of different teas, brewed by two different methods - continuous infusion and repeated infusion.

In repeated infusion, the leaves are steeped in a small quantity of hot water, and more hot water is added periodically, until the resulting infusion is extremely weak. The continuous infusion method, however, uses larger quantities of water, but the brewing is continuous.

Much of the tea-drinking populace in rural China and Asia drinks almost exclusively fluoride-rich fu-brick and black brick tea. Unlike our Western habit of brewing the leaves only for a few minutes, brick tea is traditionally brewed continuously for periods of several hours, and sometimes all day! The resultant infusion is not only ferociously strong, it is dangerously rich in fluoride. Large segments of the population where brick tea is the staple beverage show signs of skeletal and dental fluorosis. The researchers concluded that in order to prevent the development of fluorosis, "the maximum consumption of fu-brick tea and black brick tea should be 1.7 liters and 4.8 liters/day respectively" (Fung 1998).

Even to those of us who consider ourselves dedicated tea drinkers, the notion of drinking almost 5 liters of strong tea daily would be anathema. By comparison, limiting one's consumption to a modest 4-5 cups per day seems eminently reasonable.

For those who are concerned about the prospect of taking in any excess quantity of fluoride, green tea extracts may be a useful alternative - although of course it is quite possible that extracts, too, contain fluoride. Buyer beware.

References:

Fung KF, Zhang ZQ, Wong JWC, Wong MH. Fluoride contents in tea and soil from tea plantations and the release of fluoride into tea liquor during infusion. Environmental Pollution 1999;104(2):197-205. Accessed Nov 30 2006 from:
http://serve01.ecaa.ntu.edu.tw/jjchou/jjchouweb/Authorization/
Progress%20Reports%20and%20Schedules/PhD%20Student/DavidHu/PDF/BIO/Tea.pdf

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The news and other items in this newsletter are intended for informational purposes only. Nothing in this newsletter is intended to be a substitute for professional medical advice.