Yesterday’s food scare du jour was all about grapefruit, and how it apparently increases the risk of breast cancer in post-menopausal women.
As ever, we were pressed into service to comment on this to the media. Here are some points of interest:
- It’s quite a big study – a 50,000 woman cohort is something you can’t really dismiss out of hand.
- Although there were a large number of women involved in this study, ‘only’ about 1,600 developed breast cancer, which makes the statistical analysis a little harder, and the conclusions much less certain.
- Grapefruit has been show to interfere with the metabolism of several drugs.
- It’s been shown to interfere with oestrogen metabolism.
- Since oestrogen metabolism is known to affect breast cancer risk, its a fair hypothesis that grapefruit might affect breast cancer risk, and this study was designed to answer this question.
- The study relied on questionnaires, i.e. it asked women how much grapefruit they remembered eating, as opposed to following women over a period of years and actually measuring how much they ate. Questionnaire-based studies are much less reliable than ‘forward-looking’, prospective studies.
- No study has ever before shown a link between grapefruit and breast cancer risk.
- One study (albeit a very small one, on rats) suggested that grapefruit might contain compounds that actually protect against cancer.
- So, in conclusion, the jury’s still out.
That’s not to say there’s no link – the theory the study set out to test is based on sound, valid science; and we know that there’s something in grapefruit juice that can potently affect our metabolism.
However, given that we DO know a lot about breast cancer risk in general – and that we think we know why its on the increase in Western society (basically, women having fewer children later and being overweight after the menopause) – its safe to say that it’s highly likely that if grapefruit plays any role at all in the trends we’re seeing in breast cancer rates, it’s a very very small one.
And remember – eating five portions of fruit and vegetables, every day, is a great way to reduce your risk of many types of cancer.
Henry August 13, 2007
Hi Helen, glad you like the blog.
The link between having children and breast cancer is that women who have children at a younger age tend to be less likely to get the disease, as are women who have more than one child.
There’s a lot of work underway to find out why, but it’s thought to be something to do with permanent changes occurring in the breast cells during pregnancy, and also related to overall levels of circulating hormones over women’s lives. Sorry to be a bit vague, but like I said, its still a bit of a grey area.
There’s a summary of the risks and causes of breast cancer here:
and detailed, slightly more ‘techy’ info here:
Helen August 13, 2007
This blog’s very interesting and great for those of us who aren’t scientists.
I agree with above in terms of balance of this article. The instinctive reaction to seeing this story in the media is to think “rubbish, grapefruit cant be bad for you” but interesting to see that it may have a negative effect on the metabolism of some drugs.
What is the link between women having fewer children later and breast cancer incidence?
Michael August 10, 2007
You say “no study has ever before shown a link between grapefruit and br ca risk”. We’ve seen similar statements used in the media to imply it is super-important and ultra-significant. Might it have been better to say there have been other studies that haven’t shown a link (if that’s the case) or one study isn’t enough to prove a link?
But I like the tone of your blog – very balanced.