“Breast cancer risk linked to red meat, study finds,” headlined the Washington Post’s front page last Tuesday. “Younger women who regularly eat red meat appear to face an increased risk for a common form of breast cancer, according to a large, well-known Harvard study of women's health,” began the Post’s report.
The researchers studied 90,659 women aged 26-46 over 12 years. Red meat intake was assessed three times via self-administered questionnaire during those 12 years. By the end of the study period, 1021 cases of invasive breast cancer had been documented.
Contrary to the Post’s headline, however, the researchers actually reported no statistically significant correlation between red meat intake and all types of breast cancer.
Now you might think that the researchers would have stopped at that point and moved on to some other more promising health scare. Instead, they opted to dig deeper into their data. They seemingly struck health scare gold by mining an apparent statistical correlation between red meat intake and so-called “hormone receptor-positive” breast tumors – that is, tumors in which hormones like estrogen and progesterone are thought to play key roles.
The researchers reported that study subjects who consumed 10.5 or more servings per week of red meat had twice the rate of hormone receptor-positive breast cancer as study subjects who consumer 3 or fewer servings of red meat per week.
Is this result meaningful? Probably not for many of the usual criticisms that attend such human population studies, including: small study size (only 52 breast cancer cases were among the group of women with the highest red meat intake); poor data quality (no one knows with any certainty how much red meat any of these women actually consumed); weak statistics (despite the apparent magnitude of the reported 100 percent increase in risk, the result borders on statistical noise); and lack of biological plausibility (despite all sorts of speculation, no one knows with any certainty what causes breast cancer).
But there are two other compelling points to note.
First, the study results are internally inconsistent. For example, eating between 1-3 hamburgers per week was associated with increased risk for a hormone receptor-positive tumor, but eating more than 3 beef sandwiches per week was not. Bacon and hot dogs were not associated with risk for hormone-positive tumor, but other processed meats (sausage, salami and bologna) were. That’s even odder since hot dogs are, after all, just rolled up bologna.
Next – and this is a point that I find most troublesome – is the researchers’ fear-fueling claim that hormone receptor-positive cancers are on rise.
The researchers stated in their report that hormone receptor-positive cancers increased 15 percent from 1992 to 1998 among women in the 40- to 49-year age group – a group that partially overlaps with the 26- to 46-year age group in the study. For this claimed increase, the researchers cited a January 2003 study that appeared in the Journal of Clinical Oncology. I pulled the study to confirm the citation.
The study did report that the incidence of hormone-positive tumors increased by 15 percent between 1992-1998 – at least in terms of raw numbers. However, this increase was not statistically significant. In fact, the authors of the Journal of Clinical Oncology study stated quite clearly, “the increase among 40- to 49-year olds was within the limits of chance” – meaning this apparent increase was uncertain and, essentially, a non-result.
They further went on to state that, “One could argue that the increase in hormone receptor-positive tumors we observed is simply a result of the increase in the number of tumors tested for hormone receptor status, as the majority of breast tumors are hormone receptor-positive.”
So there is no firm evidence that hormone receptor-positive cancers are on the rise and, if there has been an increase, there is a plausible explanation that has nothing to do with red meat intake. It’s too bad the Harvard researchers weren’t more accurate about the Journal of Clinical Oncology study.
Finally, the Harvard study is not the first one that has looked for a possible association between meat intake and breast cancer. There have been 29 others – 25 of which (86 percent) have not reported a statistically significant association between meat intake and breast cancer – including a July 2003 study published in the Journal of the National Cancer Institute by the same Harvard authors involving the same study subjects.
It’s too bad the Washington Post reporter didn’t approach the Harvard study more skeptically – it’s the kind of shoddy research that gives a black-eye to reporters who merely regurgitate researcher media releases.