Cancer Clinical trials Medicine Skepticism/critical thinking

Obviously a male conspiracy is at work here

Two days after the holidays are over, and I’m still taking care of unfinished business from last year. Still, the study I’m about to discuss is making the rounds of the blogosphere, and because it’s about breast cancer risk I felt the need to weigh in. This is particularly true, given some of the representations of this study that are popping up in the press and in the blogosphere, particularly among right wing bloggers. Let’s start with a BBC news story about the study:

Women who exercise by doing the housework can reduce their risk of breast cancer, a study suggests.

The research on more than 200,000 women from nine European countries found doing household chores was far more cancer protective than playing sport.

Dusting, mopping and vacuuming was also better than having a physical job.

The women in the Cancer Research UK-funded study spent an average of 16 to 17 hours a week cooking, cleaning and doing the washing.

Experts have long known that physical exercise can reduce the risk of breast cancer, probably through hormonal and metabolic changes.

But it has been less clear how much and what types of exercise are necessary for this risk reduction.

And much of past work has examined the link between exercise and breast cancer in post-menopausal women only.

The latest study looked at both pre- and post-menopausal women and a range of activities, including work, leisure and housework.

All forms of physical activity combined reduced the breast cancer risk in post-menopausal women, but had no obvious effect in pre-menopausal women.

Out of all of the activities, only housework significantly reduced the risk of both pre- and post-menopausal women getting the disease.

Housework cut breast cancer risk by 30% among the pre-menopausal women and 20% among the post-menopausal women.

I’m betting that you can guess what sorts of reactions to this study are popping up. Unfortunately, as is frequently the case, few seem to have actually read the study itself, and most ignore the cautionary statements of the lead investigator or any hint of nuance in their rush to use this study to justify their ideological biases. For example, it didn’t take long at all for our old “friend” Vox Day to leap in and make a fool of himself:

Perhaps it is the specific form of light exercise that housework offers. More likely, women who live the sort of traditional lives that involve running a household and doing housework are less likely to do the sort of things that spark breast cancer, unlike your average post-feminist skank with a career and a gym membership.

Because dosing yourself with estrogen daily and having abortions can’t possibly be related to anything bad, like breast cancer, oh no. That’s just the Patriarchy’s mysogynistic scientists trying to keep women oppressed, barefoot and doing the dishes, a proper feminist science wouldn’t be allowed to publish anything that a woman doesn’t want to hear.

I honestly don’t know how Vox jumped from this study to a rant about estrogen replacement therapy and abortions, but it’s not surprising that Vox would misread this study as an indictment of feminism, given that he has the charming view that women have “fascistic” tendencies, a view that he uses to justify his view that women should not be allowed to vote. Oddly enough, he was half making sense with regards to how one potential interpretation of this study is that moderate housework could be a marker for another factor that is the real protective factor against breast cancer. Unfortunately, he couldn’t use that Mensa mind that he bills himself as having and keep himself from launching into a tirade about “skanks” and abortion–which is, to say, it was just Vox being his usual sexist self.Sadly, not surprisingly, Vox isn’t the only one jumping on this study as some sort of indictment of feminism. There’s plenty of misogyny around looking for an excuse to attack feminism. For example, we have this charming post from a guy going by the ‘nym of Heretic (you know, when I see a ‘nym like “Heretic,” I consider it a pretty good indication that the guy thinks way more of himself and his opinions than he and his opinions in fact warrant, and this “Heretic” fits that indication perfectly):

Betty Friedan, in The Feminine Mystique, claimed that, “the women who ‘adjust’ as housewives, who grow up wanting to be ‘just a housewife,’ are in as much danger as the millions who walked to their own death in the concentration camps…”. Reference

We now see that the opposite is the case. Being a housewife and mother is in fact better for women’s health. It is being a feminist that kills you.

Of course, where “Heretic” is coming from can be clearly seen from the little blurb under the title of his blog Heretical Sex:

Ideological movements are generally movements of the gullible led by the manipulative, and feminism is no exception. The feminist movement can be regarded as a taxpayer-funded religious social club run by lesbians, where women are encouraged to gather in secret for the purpose of hating men.

Charming, isn’t he? But even Heretic is not alone. How about a guy who calls himself The Eternal Bachelor:

No wonder cases of breast cancer have been rising in recent decades; women don’t do housework anymore. It’s soooo sexist (unlike expecting a man to be the main breadwinner; that’s not sexist at all, no ma’am.)

So next time some women hassle you to donate money for a charity that battles Breast Cancer, go one better than giving them cash; give them a big pile of ironing to do, or ask them to clean up your desk.

What a card. No wonder he remains an eternal bachelor.

Of course, none of these bloggers seem to have actually read the study (or at least the abstract, which is understandable to most lay people). But where would the fun be in that? It’s far easier simply to use press reports of the study as a means of confirming your prejudicies. As Erica Barnett put it:

The funniest/saddest/most ridiculous thing about this study “proving” that housework “cuts the risk of breast cancer” by 20 to 30 percent: The researchers’ actual conclusion, buried in the 12th paragraph of this BBC story, was that “moderate physical activity” of any kind–walking, riding a bike, masturbating–reduces the risk of breast cancer. So what did the BBC and other media focus on? What else–domestic servitude.

Even more interestingly, as pointed out on Our Bodies Our Blog, a similar study looking at risk factors for endometrial cancer concluded the same thing (that moderate exercise is protective) about two years ago and was spun the same way. Not surprisingly, anti-feminist bloggers like Vox, Heretic, and Eternal Bachelor were all too eager to take such spin to ever more crude and obnoxious levels.

Me being what I am, that’s the first thing I thought of doing: Reading the actual study (which is an e-pub ahead of print version and has not yet appeared in the print version of the journal). So, let’s start with the abstract:

There is convincing evidence for a decreased risk of breast cancer with increased physical activity. Uncertainties remain, however, about the role of different types of physical activity on breast cancer risk and the potential effect modification for these associations. We used data from 218,169 premenopausal and postmenopausal women from nine European countries, ages 20 to 80 years at study entry into the European Prospective Investigation into Cancer and Nutrition. Hazard ratios (HR) from multivariate Cox regression models were calculated using metabolic equivalent value-based physical activity variables categorized in quartiles, adjusted for age, study center, education, body mass index, smoking, alcohol use, age at menarche, age at first pregnancy, parity, current oral contraceptive use, and hormone replacement therapy use. The physical activity assessment included recreational, household, and occupational activities. A total physical activity index was estimated based on cross-tabulation of these separate types of activity. During 6.4 years of followup, 3,423 incident invasive breast cancers were identified. Overall, increasing total physical activity was associated with a reduction in breast cancer risk among postmenopausal women (Ptrend = 0.06). Specifically, household activity was associated with a significantly reduced risk in postmenopausal (HR, 0.81; 95% confidence interval, 0.70-0.93, highest
versus the lowest quartile; Ptrend = 0.001) and premenopausal (HR, 0.71; 95% confidence interval, 0.55-0.90, highest versus lowest quartile; Ptrend = 0.003) women. Occupational activity and recreational activity were not significantly related to breast cancer risk in both premenopausal and postmenopausal women. This study provides additional evidence for a protective effect of physical activity on breast cancer risk. (Cancer Epidemiol Biomarkers Prev 2007;16(1):OF1-7)

Basically, this is the classic example of a study in which multiple correlations were observed that, save for one (housework), approached, but did not achieve, statistical significance. Right in the abstract, it states that total physical activity was associated with decreased risk of breast cancer; it just missed the “magic” p value of 0.05 or below. Only one type of physical activity did achieve “statistical significance,” and that was moderate forms of housework. Given the magnitude of the study (218,169 women from nine different countries), the difficulty standardizing what, exactly, is meant by “light,” “moderate,” and “heavy” activity, plus the sheer logistical difficulties involved in carrying out such a massive study, this is not a particularly surprising result. To overcome some of these difficulties, the authors used a standardized measurement of physical activity that assigns a MET value (the ratio of work metabolic rate to a standard metabolic rate of 1.0) to each activity. Unfortunately, even with such care getting reliable results out of an epidemiological study like this that looks at difficult to measure risk factors is a very dicey affair indeed, as the authors acknowledge in the paper:

This study has some limitations that need to be considered when reviewing these results. Although the data collection was standardized across the nine countries included in this analysis, data were only available on past year physical activity (24), and thus the effect of physical activity in different time periods of life on breast cancer risk could not be examined. In addition, there were no data available on the frequency, duration, and specific intensities of occupational activity; hence, only categories of occupational activity were recorded. Furthermore, there were few study participants who were categorized in manual and heavy manual occupations, thereby limiting the assessment of the effect of
intense occupational activity on breast cancer risk. Finally, some misclassification of physical activity levels is likely in this study thereby introducing nondifferential misclassification bias that would have biased the results towards the null.

“Biased towards the null,” by the way, means that such misclassification, if not biased in one direction or the other, would have made it less likely that any statistically significant correlations would be found, because of the random noise introduced into the raw data by misclassification. It’s also looking at a snapshot of how much physical activity these women did in the most recent year. This estimate may or may not correlate with their activity over the years prior, when physical activity would most likely have exerted any beneficial effect.

Although I’m not as “unconvinced” as Medpundit, I do agree that there are problems with this study and that it probably does not mean that housework in and of itself protects against breast cancer any more than other moderate activity. However, I do still have to note that certain aspects of the data seem inconsistent. One observation that leapt out at me was that a 28% higher fraction of the “noncases” (women who didn’t develop breast cancer) were nulliparous (they never had children). This is inconsistent with numerous previous studies that demonstrate that nulliparity is a risk factor for the development of breast cancer. Similarly, the fraction of noncases whose age at first pregnancy was under 20 was 36% higher than among cases, again not entirely consistent with decades worth of studies that show that a young age at first pregnancy reduces the risk of breast cancer. True, taken as a whole, there was a tendency towards a younger age at first pregnancy, but the authors never stated whether any of these differences between case and noncase groups was statistically significnat; indeed, other than the trend towards a lower age at first pregnancy, these differences weren’t mentioned at all. On the other hand, as one would expect, the cases tended to be older by a few years and in the postmenopausal women, 53% more cases used hormone replacement therapy, consistent with HRT as a (now) known risk factor for breast cancer.

In other words, the characteristics of the group seem to be all over the map, which makes me wonder about how valid the correlation that they found is in actuality. I wouldn’t go so far as one wag did and suggest that, because housework was the most common activity among the women in the study that the results are like finding a correlation among breast cancers and wearing bras and trying to blame the bras, but that’s a good way of putting the results in perspective. That’s why my perspective, all can be concluded from this study is that there may be some sort of “sweet spot” for physical activity as far as producing a protective effect against breast cancer, with moderate physical activity being best. It is also possible that, as the authors speculate, that more regular moderate physical activity may be better than less frequent but more strenuous activity as far as protection from cancer. It is not clear whether one, both, or neither of these hypotheses explain this study’s results. What is clear, however, is that all too many men are so hostile to feminism and women’s taking on roles outside of that of wife and mother that they’ll leap at anything to justify their bigotry, even to the point of using gruel as thin as the results of this study.

By Orac

Orac is the nom de blog of a humble surgeon/scientist who has an ego just big enough to delude himself that someone, somewhere might actually give a rodent's posterior about his copious verbal meanderings, but just barely small enough to admit to himself that few probably will. That surgeon is otherwise known as David Gorski.

That this particular surgeon has chosen his nom de blog based on a rather cranky and arrogant computer shaped like a clear box of blinking lights that he originally encountered when he became a fan of a 35 year old British SF television show whose special effects were renowned for their BBC/Doctor Who-style low budget look, but whose stories nonetheless resulted in some of the best, most innovative science fiction ever televised, should tell you nearly all that you need to know about Orac. (That, and the length of the preceding sentence.)

DISCLAIMER:: The various written meanderings here are the opinions of Orac and Orac alone, written on his own time. They should never be construed as representing the opinions of any other person or entity, especially Orac's cancer center, department of surgery, medical school, or university. Also note that Orac is nonpartisan; he is more than willing to criticize the statements of anyone, regardless of of political leanings, if that anyone advocates pseudoscience or quackery. Finally, medical commentary is not to be construed in any way as medical advice.

To contact Orac: [email protected]

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