Shoes, Ships, and Sealing Wax

Tea time

(I originally started with a disclaimer, but it got long, so I stuck it in the extended entry below.)

The first super food I'm looking at is actually a drink: tea.

(I can't stand tea. I wish I liked it. I like the ritual, the little pots, dunking the tea bags...but yuck. And I found out Down South that anyone who doesn't like "cold ice tea" is regarded with great suspicion.)

Tea is made from the leaves of the Camellia sinensis plant; steamed leaves are used for green tea and the leaves that are oxidized are black tea. I've seen it called the most widely used beverage in the world (although I suspect water ranks higher), and one of the things that has caught the interest of researchers is that areas of the world with high green tea consumption (like China and Japan) have lower rates of cancer than are seen in the west.

This brings us to some epidemiologic studies. For example (and I pulled these from a PubMed search):

Green tea consumption enhances survival of epithelial ovarian cancer.

Our study investigates whether tea consumption can enhance the survival of patients with epithelial ovarian cancer, a prospective cohort study was conducted in Hangzhou, China. ...

We conclude that increasing the consumption of green tea post-diagnosis may enhance epithelial ovarian cancer survival.

Zhang M, Lee AH, Binns CW, Xie X. (2004)

and from 1997:

Green tea consumption and the risk of pancreatic and colorectal cancers.

An inverse association with each cancer was observed with increasing amount of green tea consumption, with the strongest trends for rectal and pancreatic cancers. For men, compared with non-regular tea drinkers, ORs among those in the highest tea consumption category (> or = 300 g/month) were 0.82 for colon cancer, 0.72 for rectal cancer and 0.63 for pancreatic cancer, with p values for trend being 0.38, 0.04 and 0.04, respectively. For women, the respective ORs for the highest consumption category (> or = 200 g/month) were 0.67, 0.57 and 0.53, with the respective p values for trend being 0.07, 0.001 and 0.008. Our findings provide further evidence that green tea drinking may lower the risk of colorectal and pancreatic cancers.

Ji BT, Chow WH, Hsing AW, McLaughlin JK, Dai Q, Gao YT, Blot WJ, Fraumeni JF Jr.

and

Tea consumption and the reduced risk of colon cancer -- results from a national prospective cohort study.

This study examines the relationship between tea consumption and colon cancer risk in the US population. ...

This study suggests an inverse association between colon cancer risk and habitual tea consumption.

Su LJ, Arab L. (2002)

But you can also find

Tea consumption and risk of bladder and kidney cancers in a population-based case-control study.

This study offers only minimal support for an inverse association between tea consumption and bladder or kidney cancer risk.

Bianchi GD, Cerhan JR, Parker AS, Putnam SD, See WA, Lynch CF, Cantor KP. (2000)

and

Consumption of black tea and cancer risk: a prospective cohort study.

This investigation does not support the hypothesis that consumption of black tea protects against four of the major cancers in humans; a cancer-enhancing effect was not evident, either.

Goldbohm RA, Hertog MG, Brants HA, van Poppel G, van den Brandt PA. (1996)

So there you have it: tea may protect against cancer. Or not.

I work with chemists, so I know there's more to tea than tea. For example, there's this polyphenol in tea, epigallocatechin-3-gallate (called EGCG for short), that has been examined on its own, away from the "How many cups of tea did you drink a day when you were smoking cigarettes after you'd been diagnosed with cancer?" studies. Looking at people is great, but how about what goes on in vitro?

Treatment of epigallocatechin-3-gallate inhibits matrix metalloproteinases-2 and -9 via inhibition of activation of mitogen-activated protein kinases, c-jun and NF-kappaB in human prostate carcinoma DU-145 cells

The inhibition of MMP-2 and MMP-9 in DU145 cells by EGCG is mediated via inhibition of phosphorylation of ERK1/2 and p38 pathways, and inhibition of activation of transcription factors c-jun and NF-kappaB. EGCG may play a role in prevention of invasive metastatic processes of both androgen-dependent and -independent prostate carcinoma.

Vayalil PK, Katiyar SK (2004)

Okay, I'm not going to pretend that I actually know what that means. Here's my extemely basic version of the gist of it and similar studies:

You take cancer cells and stick them on a petri dish where they keep growing. If you add this chemical, EGCG, the cells stop growing. Ergo...maybe having lots of EGCG in your body stops cancer cells from getting out of hand and that's why people who drink lots of tea don't die of cancer.

(In between the studies of humans and the studies in glass there are animal studies...rats, mice, and hamsters either being fed tea or getting shots of EGCG. The results seem to be pretty much the same, so I won't quote any more here.)

There are actually a bunch of chemicals in tea (epigallocatechin, Pheophytins A and B, catechin, et al) that may affect the body. Some studies are looking at anti-inflammatory action that may be good for the cardiovascular system. Something in tea may kill bacteria that builds up in the mouth, so tea drinkers have fewer cavities.

So it looks like tea may actually be pretty good for you.

I'd drink it all the time...if it didn't taste so nasty.

Here's my "super food" post disclaimer (or why you shouldn't believe anything I say anyway.):

There are a lot of reasons why (to use the article I cited yesterday as an example) "Oleic acid, the main monounsaturated fatty acid of olive oil, suppresses Her-2/neu (erbB-2) expression and synergistically enhances the growth inhibitory effects of trastuzumab (HerceptinTM) in breast cancer cells with Her-2/neu oncogene amplification" becomes Olive oil 'is cancer key' when it hits the newspaper.

There is a risk that the scientific studies as presented in the popular press end up over-simplified, and with conclusions drawn that were never meant to be drawn. Reporters usually aren't scientitists, and often scientists aren't spectacular at dumbing things down enough for lay people. You can lose some subtle but significant nuance in the process. (Science communication was actually my area of study in school, but I'm certainly not great at it. All it really got me was an appreciation for how tricky it is.)

So when reading about the findings of health studies, one should not just leap at the diet fad of the month. One of the best guides to interpreting studies I've read is in Walter Willett's Eat, Drink, and Be Healthy. I'd quote from it, but I can't find my copy. (Probably because I lent it to somebody...I've pressed this book on lots of people, because I think it is very good.)

Anyway...as I've started reading up on the super foods, I'm finding lots of specific studies cited, and I'll probably end up citing them too, especially when I can get my hands on the actual papers. Essentially I'm reading this stuff from two angles...I'm reliving my science reporter days, and I'm trying to decide what to have for lunch. But I am not trying to come across like an expert, nor am I telling anyone else what to eat, and I apologize in advance if I sound like I am.

Posted by Nic at January 13, 2005 08:10 PM