Monday, September 20th 2010
I use PubMed to make RSS feeds out of searches on topics relevant to my research, because I cannot be trusted to regularly look this up on my own (I also have feeds from many of the main journals in my field, natch). One of my searches, “inflammation endometrium,” turned up an interesting article today from the European Journal of Cancer. Friedenreich et al review the literature on physical activity and cancer prevention and find a consistent relationship between physical activity and reduced risk of several cancers. Obviously, I want to focus on breast, endometrial and ovarian cancers, since those are the stuff of ladybusiness.
Breast cancer
The authors found seventy three separate studies on breast cancer (they say separate, I assume, to differentiate multiple publications on the same data set). Three quarters of the studies found physical activity to have a positive effect on breast cancer risk; within those, the risk reduction tended to be around twenty five percent when comparing most to least active participants. Interestingly, postmenopausal physical activity seemed to have the strongest effect, which was a bit of a surprise to me. What this says, to me, is that adjustments to lifestyle made late in life can still have significant effects on health. If you were a couch potato when young but are committed to physical activity now, all is not lost.
Endometrial cancer
For endometrial cancer, the authors concluded that “physical activity probably protects against endometrial cancer” (p. 2594, anyone else find that wording odd?). There were twenty studies of endometrial cancer, so far fewer than of breast cancer, but the reduction in risk was very similar, of twenty to thirty percent. Sedentary behavior appears to increase risk (like jobs where you sit all day), and more intense or longer bouts of activity tend to have more positive effects.
Ovarian cancer
Here, the authors found conflicting evidence, where some studies found risk reduction with physical activity, some found no effect, and one found a risk increase with physical activity. There were about twenty studies that looked at ovarian cancer, but the authors claim that the sample size was often small.
What surprised me about this section was what little attention they paid to mechanism. Ovarian cancer is different from breast or endometrial cancer: a big part of what researchers think causes it is the “incessant ovulation” of industrial societies. That is, women in industrial populations, due to a positive energy balance, low rates of childbearing and low rates of breastfeeding, have as many as 400 menstrual cycles in their lives, compared to only 50 in a forager population, which would have a later age at menarche and women who are often pregnant or breastfeeding. Continual insults to the ovarian tissue, from the rupture of the ovarian wall during ovulation, and its subsequent repair, increase the risk of cell mutations. Small differences in sedentary or active behavior don’t tend to be enough to keep a woman from ovulating.
Why parse out physical activity and sedentary behavior?
You may have noticed that I mention different kinds of physical activity, but also sedentary behavior. In the paper the authors go into far more detail about different types of behavior, from domestic activities to occupational activities to recreational ones, and whether they are physically active or sedentary. It is important to consider both of these factors because they contribute to an overall lifestyle that can tip the balance towards a more positive (more calories in than out) energy balance, or a more negative (more calories out than in) energy balance.
Let’s take my Polish field site for instance, the Mogielica Human Ecology Study Site, directed by Grazyna Jasienska. These women burn on average more calories than urban US women (Clancy et al 2009). Women there work alongside the men to do all the agricultural work needed to run their farms. You could just stop there and say that is very different from many populations within the US. But these women also do all their own housework and cooking, they have gardens, if they work they walk or take the bus. They are often sweeping and mopping instead of vacuuming. They spend a lot less time in front of screens, like televisions or computers (they have them for sure, but there are fewer desk jobs in front of a computer there). At least from my observations, they are less likely to order things online, and instead go to the store.
So the lifestyle differences, comparing an urban, sedentary person with a desk job in the US to a farmer in Poland, become far more striking, as do the number of calories they likely burn each day in their daily lives.
Is there population variation in cancer rates?
I thought you’d never ask! The main reason I decided to write about this article was so that I could highlight one of the most elegant, simple little graphs I have ever read, from a 2001 article by Jasienska and Thune. They compare population averages in progesterone (a female reproductive hormone) with breast cancer rates. Here’s the graph:
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| Jasienska and Thune 2001 |
Guess what is one of the biggest predictors of progesterone concentrations? Physical activity.
Finally, why someone else should always read your manuscripts
There were a few tough sentences in here that a copyeditor could have really improved. The authors wrote:
“There is strong and consistent evidence that physical activity reduces the risk of several of the major cancer sites, and that between 9% and 19% of cancer cases could be attributed to lack of sufficient physical activity in Europe” (p. 2593, abstract)
Which I tweeted, and to which Alex Wild of Myrmecos responded:
“@KateClancy So if Europeans were more active we’d all have less cancer?#wordingfail”
And then as I was preparing this post, I found:
“Physical activity reduces breast cancer risk when performed at any age throughout life, but activity done after the age of 50 years does have a stronger effect on risk than activity done earlier in life and sustained lifetime activity is of benefit” (p. 2594).
So, sustained lifetime activity isn’t as good as activity after 50, or this is a point independent of which time of activity matters? I thought perhaps they were trying to make points about both? Copyeditor, please!
Anyway, this article was a fun way to get to share a broader perspective on reproductive cancer rates in women across the world. Share your thoughts or questions in the comments!
References
Clancy, K., Ellison, P., Jasienska, G., & Bribiescas, R. (2009). Endometrial thickness is not independent of luteal phase day in a rural Polish population Anthropological Science, 117 (3), 157-163 DOI: 10.1537/ase.090130
Friedenreich CM, Neilson HK, & Lynch BM (2010). State of the epidemiological evidence on physical activity and cancer prevention. European journal of cancer (Oxford, England : 1990), 46 (14), 2593-604 PMID: 20843488
Jasienska, G., & Thune, I. (2001). Research pointers: Lifestyle, hormones, and risk of breast cancer BMJ, 322 (7286), 586-587 DOI: 10.1136/bmj.322.7286.586
Friday, September 17th 2010
The “Around the Web” series highlights informative websites, and also targeted blog posts and news articles, relevant to the courses I teach. This semester I teach Anth 143: Biology of Human Behavior, an introductory-level course that covers the basics of evolution, behavioral biology, and the interaction of biology and culture. My hope is that these posts are useful not only for my current students, but other people hoping to gain background or insight into these topics.
This week we covered mating and marriage systems. However, I combed through my enormous bookmarked list of interesting posts and articles, and found very little. So I decided to beef up this week’s “Around the web” with a few selections that every student should read, regardless of whether it relates to this particular class. But first, SCIENCE!
Mating and marriage
First, Greg Laden reviews and reflects on a very cool PLoS Genetics paper on polygyny and human diversity here. This is well written and defines a few important terms for intro anthropology students.
Here is a link to material on polygyny from a course taught by Robert Quinlan at Washington State University. Great information… and mentions the Dogon of Mali and Strassman’s test of the Polygyny Threshold Model, which we discussed in lecture. This is great for review or clarification.
Some interesting food for thought from Savage Minds on the “end” of marriage (said with lots of foreboding).
Resources for learners
These articles don’t particularly fit into any of the categories of this class, but are resources I want you to have. So here you go:
First, the frivolous but fun: the San Diego Ape Cam and Panda Cam. Also, the physics of mega shark vs. plane. Just click on it, trust me.
The science behind why chimpanzees are not pets, by a truly excellent scholar Brian Hare. We’ll be watching a film that features his work later in the semester, Ape Genius.
There are a lot of people who first found their love of science through reading Stephen Jay Gould. So here is a link to the unofficial SJG archive.
Now for some links on learning:
Thursday, September 16th 2010
I am slowly re-posting some work from my lab blog. This one received quite a bit of traffic. I actually have a follow-up in the works, so watch for it!
You have probably seen the buzz about the recent American Journal of Obstetrics and Gynecology article (Wax et al 2010) on home birth safety, and the editorial in the Lancet that took the article’s shaky meta-analysis to crazytown: “Women have the right to choose how and where to give birth, but they do not have the right to put their baby at risk,” they write.
I have a lot of thoughts about this study and how it has been covered, by medical doctors and by the media. My main issues revolve around: 1) what these statistics mean from a personal versus a public health perspective, 2) maternal recovery and mortality, 3) the problem with criminalizing home birth, 4) the literature around birth experiences and the process of birth and resources for women, and 5) how we should look at this topic in the future.
What do these statistics mean?
According to the Wax et al (2010) meta-analysis, the difference in infant mortality between hospital births and home births is 0.2% versus 0.9% (other people have already done a nice take-down of the cherry-picking of older studies that have received significant criticism, yet were included). While headlines have screamed that this is a three-fold difference, it makes sense for us to pay attention to the absolute values. Infant mortality, in hospital or home births, is under one percent. We can’t even say that one in one hundred babies die in childbirth in developed countries any more (at least not as a whole – for now I’ll side-step some major differences relating to social disparities and race). If you are pregnant and considering where you want to give birth, I’m not sure how this slight difference could really sway you one way or the other. The problem is that the editors of the Lancet (and others) are conflating public health recommendations with personal recommendations… and shaming women in the process.
From a public health perspective, I suppose I can grudgingly understand why the difference in infant mortality in home versus hospital births matters. But you cannot take population-wide statistics and apply them to individuals. To do so is to ignore inter and intrapopulational variation, and to take a women’s decision about her body out of the context in which it should be understood.
Another thing to notice, Wax et al (2010) found that “neonatal outcomes of planned home births revealed less frequent prematurity, low birthweight, and assisted newborn ventilation.” So of the more than 99% of babies who were fine, home birth babies tended to be healthier. This of course could be a bias of who chooses a planned home birth versus someone who does not, so I am not assuming the directionality to be that the home birth predicts healthier kids. But I wouldn’t be surprised if further analysis showed both directions to be causal; that is, that women more likely to have healthier kids choose to plan a home birth, but also that because home births have fewer interventions those kids are more likely to be healthy.
What about maternal health?
What the Lancet editorial and Wax et al (2010) mention only briefly, is that for maternal mortality and morbidity in low-risk births, to me, home births (and, I would contend, birth center births) are the clear winner. By not being in the same room as epidural medicine (it’s right behind you in big cabinets, just waiting for you to say “ow”*), single beds with little room to maneuver, continuous fetal monitoring and an IV under your skin as soon as you’re admitted, you avoid interventions that often carry their own significant risks and precipitate a cascade of other interventions.
Many women in the US don’t want to give birth in hospitals because being in a hospital increases the risk of maternal mortality and morbidity and, perhaps more importantly, slows recovery time. I say the recovery time issue may be more important, because while the US is embarrassingly bad at keeping mothers alive, the numbers are still better than in infant mortality (though, obviously, this makes sense from a life history perspective). The US is ranked 40th in the world in terms of maternal mortality – that means 39 countries do a better job keeping women alive during childbirth. Our incidence of maternal mortality is increasing, not decreasing, with the latest figures for 2008 being 17 deaths out of 100,000 births (Canada, for instance, has 7/100,000). Developed countries with higher rates of home birth have lower rates of maternal mortality.
Criminalizing home birth
Another problem I have is that part of the reason they cite home births as unsafe is that so few of them are staffed by certified midwives (only one third according to the Lancet editorial). The only reason more home births are not staffed by certified midwives is that organizations like the American Medical Association and others have lobbied to keep home births illegal in many states. Midwives cannot legally help a family give birth at home where I now live, in Illinois. Instead, I have been told by local homebirth supporters that there is an underground movement of lay midwives who try to help women stay out of hospitals, if it’s what they want. Is this a safe way to give birth if you are low-risk? Maybe, maybe not. I’m not sure I would be keen on a home birth that did not have a Certified Professional Midwife or Certified Nurse Midwife attending, who also had a good relationship to a doctor at the nearest hospital. But I also would not want to give low-risk birth in a hospital, even if I had a midwife, because of the major risks you incur just by stepping into a hospital (like infection). Women in states like mine are stuck between a rock and a hard place: give birth at home and risk not having someone with the right qualifications (and potentially face legal action), or risk giving birth under conditions where you may have interventions you don’t want, and treated like something less than human (which I’ll get to more in the next section).
By criminalizing home birth, medical doctors and their lobbyists force women who don’t want a medical birth to find less-than-perfect alternatives. So when Lancet editors and others criticize US women for not having the right people at their home births, I call shenanigans: they were complicit in making the laws that prohibit it in the first place.
Birth experiences in hospitals, birth centers and the home
There is a huge literature already on the medicalization and pathologization of femaleness, and I encourage you to devour it all, from Emily Martin’s The Woman in the Body to Robbie Davis-Floyd’s Birth as an American Rite of Passage.
So the other issue I want to make sure to include here is that pregnant patients don’t have the same rights as non-pregnant patients in a hospital (link to pdf), to refuse treatment, to leave, to contest a decision; hospitals can and do get court orders to force pregnant women to receive treatments they have refused. On the one hand, I can understand that sometimes decisions need to be made quickly during labor. On the other hand, I think there is a problem when we place a fetus’s rights above that of its mother’s. This recent story of police violence against a pregnant woman links to several problems with pregnant patient rights. Here are examples of court-ordered interventions. And here is more information on pregnant patient rights.
These are other reasons many women find the idea of a hospital birth frightening, and thus choose home birth or a birthing center. And if you read Davis-Floyd and others, you will see the interviews of women who have had hospital births how they were disempowered by the experience. This isn’t to say there aren’t many, many women who aren’t totally satisfied with hospital births, and would never consider home birth. It’s just to say that to acknowledge differences in infant mortality risk that are not necessarily meaningful to an individual making a decision about this, in the absence of all this other information, is disingenuous on the part of the editorial writers at the Lancet.
Future work on this topic
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| My daughter, just born at the birth center. |
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Rather than blaming the women who are trying to make the best decisions for themselves and their families and fetuses, medical doctors should be doing more to make different kinds of birth options available for women. In 2008, I gave birth in a birth center that was across the street from a hospital – the Cambridge Birth Center in Cambridge, MA. I had midwives, doulas, a labor and delivery nurse, my husband and sister to help me. I had a nice big king-size bed, a big tub to labor in, and just about every device you can think of to help me labor and push out the baby, from floating noodles for the tub, to a yoga ball, to a birthing stool. The time to get from the birth center to operating room if there was a complication was 4 minutes – the same amount of time had I been in the delivery room at the same hospital. This option is not available to me now, as a resident of the state of Illinois.
I’d like to see is re-analysis of the literature, where only home births with a certified midwife are analyzed. This is what is possible if we allow women more choices in where they give birth, so this is what we should examine. When we decriminalize women who don’t want the higher risk of epidurals or cesareans or infections, when we provide women more options for how and when to labor and give birth to their babies, and when we are honest with the failings of the medical system towards pregnant women and women in general, we’ll be heading in the right direction.
References
Wax, J., Lucas, F., Lamont, M., Pinette, M., Cartin, A., & Blackstone, J. (2010). Maternal and newborn outcomes in planned home birth vs planned hospital births: a metaanalysis American Journal of Obstetrics and Gynecology DOI: 10.1016/j.ajog.2010.05.028
Editorial staff (2010). Home birth–proceed with caution. Lancet, 376 (9738) PMID: 20674705
*What bothers me about epidurals and narcotics is not that women choose to use them during birth. I have given birth, I know how much it hurts and how it feels like the pain will never, ever end. I would never, ever begrudge a woman for choosing pain relief under those circumstances. What bothers me is that it is presented almost as a given in most hospital settings these days, since the medicine is already in the mother’s hospital room. There are many interventions one can give for pain that are not pharmaceutical, but few doctors are trained in these interventions. My midwives and doulas had so many tricks up their sleeves that even though I was in excruciating pain, I was able to remain in the birth center and have a totally normal, natural childbirth. I also want to be clear that if I hadn’t clearly stated I wanted this in my birth plan, they would not have worked so hard to make this possible. I wanted to be kept out of the hospital, kept away from the risk of infection and the risk of narcotics and the risk of cesareans and episiotomies, so they helped facilitate that within what was safe for me and my baby.
