Wednesday, July 18, 2007

Beware the Evil Grapefruit

The article said something like this: "Avoid Deadly Grapefruit". No, that was just how it came across to some readers. Somehow between the actual article in British Journal of Cancer and the press release, and then the newspaper article, though, that's what it became. Reading the actual paper in the journal is difficult for most people not just because Sturgeon's Law is true of research papers, but also because access to medical journals is limited for people who don't work near a medical research library. I read the paper, and it's pretty much Bullsh*t, although not as bad as the newspaper version made it sound.

Epidemiological studies can be helpful at revealing further avenues of inquiry, but they are not proof of anything. The other epidemiological study that invariably comes out saying the opposite will also get big headlines, but the clinical study that disproves both of them will be ignored.

"In epidemiologic research, relative risks [RR] of less than 2 are considered small and usually difficult to interpret. Such increases may be due to chance, statistical bias or effects of confounding factors not evident"
National Cancer Institute, "Abortion and Possible Risk for Breast Cancer: Analysis and Inconsistencies," October 26, 1994

In this study, the only patients with a RR greater than 2 were the ones currently taking estrogen/progestin therapy. The highest RR for the greatest consumption of grapefruit? 1.30. Any lower and the headline would have been saying that "Grapefruit Saves Lives".

So, the really interesting stuff from this particular study (in my opinion) didn't make news:
This finding of a reduced effect of grapefruit in women with a higher BMI is similar to the lower effect of ET on breast cancer risk in women with a higher BMI

That is, these meaningless increases in risk are even less meaningful for fatter women. That's a relief, isn't it?

Consistent with other studies on postmenopausal oestrogen use, we found an increase in breast cancer risk, particularly among current EPT users.

And post-menopausal hormone use really is risky, just like everyone else was saying.


Kristjan Wager said...

The link between homone use and breast cancer has been even futher documented Confirmed: A Link Between Breast Cancer and Hormone Therapy

Kaethe said...

It's important to distinguish between all hormone use and post-menopausal replacement hormones. Data which only has a binary for hormone use, and doesn't distinguish between types and times, really isn't helpful.

Kristjan Wager said...


Danish newspapers reported on the so-called cancer-grape fruit link today, and what's more, they were quoting the Danish Cancer Society (which Danish name actually translates as "The Fight Against Cancer"). I've long suspected that that particular organization was low on science, and this verifies it.