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.