Angry Toxicologist

Well, we've gone over why tea supplements aren't a good idea, but the question of chemoprevention by drinking tea is still up in the air. I thought it would be interesting to lay out what's been done. Let's start with the basics:

How would tea inhibit carcinogensis?

No idea. There are dozens of ways in which tea or tea components can inhibit cancer based on speculation from tests done in cell cultures but no one knows whether any of them are relevant in a human body. Interestingly, in many studies, caffeine does as well as tea alone.

What have animal studies shown?

Tea works on all cancers. It's amazing. It's a wonder drug. Out of 110 studies, tea has a protective effect against tumor formation or progression in 92 studies, with no effect in the other 13. Pretty good, eh?

So what have the human studies shown?

Hmmm...not so wonderful after all. The large majority of studies of tea and cancer found no association, and for some cancers (kidney & bladder), more studies found an increase risk than a decrease. And for those that you would expect for there to be a large effect from tea, there is none. Take colon cancer. Most of the tea components aren't very bioavailable (the body doesn't take them up very well) so one would expect that the cancers in the GI tract would respond more than others. Not so. In spite of all this, researchers still try to come up with convoluted mechanisms for why things should work (the best stretch is the suggestion that black tea may inhibit breast tumorigenesis by decreasing fat absorption and therefore affect hormone metabolism). The take away for this section is that for no cancer type have the number of good studies showing protection out numbered the good studies that found no association or harm.

Go ahead and drink your tea
or, your coffee, or whatever but do it because you like the way it tastes, not because you think it's healthy. Also, caffeine isn't good for you chronically so keep it decaf most of the time.

It think it's instructive that many times caffeine or coffee seems to have the same inhibitory effect on cancer models and in fact, many of the human studies have found positive effects with coffee (sometimes the caffinated works sometimes the decaf works), yet nobody goes on and on about the cancer preventitive effects of coffee (with good reason). Why? Because it's western (read: non-exotic), common, and either associated with diners or the commercial Starbucks. Neither say 'this is healthy' (one says 'this is a staple', the other, 'this is a treat').

What does tea say? "I'm a poser and you've been duped, sucka!"

Read a good review of what's been done here (make sure you put on your skeptic's hat while reading): "Inhibition of Carcinogenesis by Tea Constituants".