nos-trum. pronunciation: \nos'-trum\. noun. Etymology: Latin, neuter of noster our, ours.
1. a medicine of secret composition recommended by its preparer but usually without scientific proof of its effectiveness.
2. a usually questionable remedy or scheme.
See here for more discussion.

Sunday, October 31, 2010

STUDY: Green Tea and Breast Cancer

The hypothesis that drinking green tea can prevent breast cancer (and other diseases) has been floating around for years.  Still no definitive evidence for it, though.

The latest in a series of studies (Breast Cancer Research, 29 Oct), attempting to pin down whether compounds found in green tea can prevent cancer, is a fairly decent population-based, prospective assessment of the breast cancer incidence between those Japanese women who drink green tea occasionally and those who drink 5 cups or more a day.

Bottom line:  no difference.

I'm not sure where the hypothesis came from that green tea--and specifically the biologically active catechin present in green tea but not in black tea--can lower the risk of cancer.  I think it was just a simple observation that Japanese women are at less risk for breast cancer, so, what is it they do different?  Well, they drink a lot of green tea.

Ethinic groups differ in hundreds of ways that population genetics or behavioral studies have yet to define.  So it seems a reach to me, implicating green tea...but all such questions are worthy of a look.  Initial studies were pretty bad.  Some showed a protective effect, some didn't.  But they were mostly small and retrospective in design:  a weakness, because you don't know, when looking back in time, whether you're defining the result in advance (remember the Texas Sharpshooter Fallacy?

The strength of this study is that it is prospective.  They took a population from a starting point, defined the result they were looking for, then followed them for years (13).

For Onion Peelers,
Compared with women who drank less than one cup of green tea per week, the adjusted hazard ratio (HR) for women who drank five or more cups per day was 1.12 (95% confidence interval (CI) 0.81 to 1.56; P for trend = 0.60) in the baseline data. Similarly, compared with women who drank less than one cup per week, adjusted HRs for women who drank 10 or more cups per day were 1.02 (95% CI 0.55 to 1.89; P for trend = 0.48) for Sencha and 0.86 (0.34 to 2.17; P for trend = 0.66) for Bancha/Genmaicha [two types of green tea]. No inverse association was found regardless of hormone receptor-defined subtype or menopausal status.

The last sentence is important because there are genetic markers for hormone receptors that indicate higher risk of more aggressive breast cancers.  It's conceivable that green tea could act more (or less) effectively on these subgroups.

You can always criticize the results by suggesting that not enough of the compound (presumably catechin, but nobody's pinned down any particular chemical here) was consumed, even in women who drink a LOT of green tea.

And you won't be surprised to find that the herbal medicine crowd has already made that claim.  Fair enough...but it seems to me that if 10 cups a day doesn't hack it, how much would?  And, if green tea is the magic potion that explains the lower risk in Japanese women, why wouldn't there be a detectable dose relationship at the levels in this study?

Green tea products, and herbal products in general, have little reliable science to show for themselves at this point.

But it's a multi-billion dollar industry.  We can expect hundreds of additional studies.

Doc D
[Note:  the link to the original study is to a provisional draft.  This link will change at some point.]

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