The Big Green Book of Tea Science

A few days ago, I finished a 770-page book on tea science.  It took a long time to get through and really challenged my understanding of chemistry, biology, agronomy, medicine, technology, and so on.  However, there were three paragraphs near the end in the chapter, “Physiological and clinical effects of tea,” that really struck me as a great, level-headed perspective on where tea science hits the media and public understanding.  And, they’re some of the least technical bits in the book.  I share them with you here:

Even at their most extreme value, none of these constituents, except possibly one or two of the inorganic ions, make anything more than a trivial and clinically insignificant contribution to nutritional requirements for energy, proteins, vitamins or minerals.  This has not, however, prevented apologists for the health-giving and medicinal properties of tea from making unjustified and unsustainable claims for it.  Many of the ‘therapeutic’ effects of tea are undoubtedly due to its water content.  Others could be due to pharmacologically active substances, not all of which have necessarily been identified. Probably most important of all is the placebo effect, especially if the person prescribing the tea believes in its healing properties.

As far as the adverse effects of tea are concerned, these, when they have been established at all, have mainly been attributed either to its caffeine or polyphenol content; but unknown or unidentified toxins—which occur in all foods of plant origin to a greater or lesser extent—may also be implicated.  More often than not, however, claims for the toxicity of tea, like those for its therapeutic efficacy, are based upon unwarranted extrapolations from inadequate data.  They often not only ignore all quantifiable considerations—which is the most heinous of all crimes in clinical toxicology—but confuse association with causation, an equally heinous crime in epidemiology.

Much of the knowledge relating to the acute pharmacology, including the pharmacokinetics and pharmacodynamics, of caffeine in man has been obtained from volunteer and other studies using the pure compound.  On the other hand, almost all of the knowledge relating to its toxicology has been inferred either from short- or long-term studies in animals.  It is therefore of dubious relevance to man.  Even more indirectly evidence of its long-term toxicity derives from epidemiological studies, mainly on coffee, but sometimes on coffee, tea and other caffeinated beverages.  Dissection out of long-term toxicity effects due solely to caffeine from those due to other constituents of the caffeinated beverages has only occasionally been attempted, and the justification for doing so has not always been accepted…

In short, there simply hasn’t been enough science done to realistically come to most of the conclusions (positive or negative) about the consumption of tea.  As I often say in my classes, “it’s more complicated than that.”  If you hear a clear-cut benefit or danger related to consuming tea, take it with a grain of salt because the reality, or our knowledge of it, is probably not that simple.

8 thoughts on “The Big Green Book of Tea Science”

  1. I remember when you mentioned this book on Twitter. There is a certain irony about your conclusion here in your post and the final paragraph. “In short, there hasn’t been enough science done to realistically come to most of the conclusions about the consumption of tea.”

    And yet, the science has somehow yielded a 770-page text. I find the science of tea fascinating. What is the name/author/pubisher of the text you read. I won’t pretend that I can possibly understand any of it, but I am interested in taking a look at it (if I can track it down through my various University contacts!).

    However, despite your conclusion here, were you able to garner useful information from it for you wiki?

  2. Hi Tea Geeks — very happy to have stumbled on your site. I’ve spent hours trolling the web and scouring a couple of books today trying to definitively ascertain whether shade-growing the tea plant increases or decreases the caffeine content. One green tea website states categorically that it INcreases it but what I can find on the net in terms of Abstracts of studies suggest that sun and shade has no effect on the caffeine. Logic tells me to disregard that one website but I can’t let it go. You strike as a guy who would not say one way or the other unless you had proof. Yes? (Thanks for any light you can shed)

  3. Ah yes, sorry about that–the book is Tea: Cultivation to Consumption, edited by K.C. Willson and M.N. Clifford (1992, Chapman & Hall). It’s out of print but Tea Geek business members can check out my copy as part of the included Tea Library Service. Sign up at

    Peter, I have gotten–and continue to get–useful information out it for the wiki. The thing is that many of the questions that are asked about tea when I do my classes are ones where there just isn’t enough science to answer. Of course, that doesn’t stop most businesses in the tea industry from giving very clear answers to those same questions, it’s just that there isn’t any scientific backing to many of them.

    Michaelle, I actually got into a big discussion about the shading-vs-caffeine issue a few months back and it sort of ended in a general consensus of the people involved but nobody ever provided any sources or citations. In other words, there was no real, accurate answer that I’d be willing to share, but everyone else involved may well be giving the consensus as the “correct answer.” However, if you’d like me to actually research the question I’d be happy to do that. Specific research requests can be made here:

  4. Michael,

    Tea: C to C is one of the best out there. I loved the aroma and production chapters. Too bad there has not been a followup in the last 18 years.

    See you sometime,


  5. I searched for a copy for months to find one. As far as I know, they’re not in print any more and you have to find a used one for sale on the open market. If you hear otherwise, let me know!

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