My take on “Is Breast Truly Best?”

bficon-web
So I’m a little late to this party, but I thought I’d add my two cents about the “Is Breast Truly Best?” study that recently came out in the journal Social Science and Medicine. This study, which analyzed the effects of breastfeeding using 25 years of data from the National Longitudinal Survey of Youth, got a ton of media coverage. You might have seen the Daily Mail headline, for example: “Breast milk is no better for a baby than bottled milk.”

Naturally, in light of the horrendous media coverage, researchers and other folks interested in breastfeeding felt they needed to put their interpretations of the study out there. People used blogs to point out the problems with the media coverage and to help readers better understand how the study was performed and what it actually showed. If you are interested, you can take a look at the posts about this study on Mammals Suck, Biomarkers and MilkResearch The Headlines, Behind the HeadlinesEvolutionary Parenting. There has been a lot of great coverage already, but I think all of this attention has also highlighted some frequent concerns about population health research. I got in touch with Cynthia Colen, the study’s lead author and another Robert Wood Johnson Health & Society Scholar alum to help set the record straight about some of the aspects of the study that have proven more controversial. And, of course, I’d like to provide my take on what this study adds to the field.

The Study: Design and Rationale

I’ll start with just a little background on epidemiological studies of breastfeeding. If you have done much research or reading in this area, then you know population-scale studies of the benefits of breastfeeding are TOUGH. Breastfeeding is so tied to other factors with a strong effect on health and wellbeing outcomes, like socioeconomic status and race, that even when we try to control for those things we usually can’t completely remove their influence upon the data. For example, in the US, roughly 75% of white mothers breastfeed whereas only 60% of black mothers breastfeed. And even in places like Sweden, where there is strong support for new families, women of higher socioeconomic status are more likely to breastfeed. Therefore, when a study shows, for example, that breastfed infants have higher IQs, we can’t be entirely confident that this result isn’t just due to residual confounding associated with the general boost in wellbeing that comes along with belonging to a more affluent family.

In population health studies, one way that researchers try to get around this confounding problem is by performing within-family comparisons. In a normal epidemiological study, we try our hardest to adjust for things like socioeconomic status, hoping that we can make fair comparisons between families–but knowing that we can never completely account for the effects of these factors. By performing within-family comparisons, we are relieved of having to make these tough adjustments. Because we are comparing kids that belong to the same family, if we find that breastfeeding, for example, is associated with some health benefit, we can be more confident that this is not just the result of residual confounding. After all, these kids share exactly the same home environment. In the population health researcher’s bag of tricks, this is an important one!

Given the problems so many existing studies on breastfeeding and health/development studies have encountered, Colen decided to find a dataset she could use to perform this type of within-family comparison. This is what led her to the National Longitudinal Survey of Youth study. This dataset has a number of strengths. First, it’s relatively large. It contains information on 11,504 children and 4,932 mothers. Second, the information on breastfeeding was collected prospectively. That is, the mothers were asked whether they breastfed while their kids were babies, rather than being asked years later (when the outcomes were assessed). This is important, as memory really fades as time goes by!  Third, there was information on 11 different health, behavior, and academic outcomes: (1) BMI; (2) obesity; (3) asthma; (4) hyperactivity; (5) parental attachment; (6) behavioral compliance; (7) reading comprehension; (8) vocabulary recognition; (9) math ability; (10) memory-based intelligence; and (11) scholastic competence. Not bad!

So armed with this data, Colen et al did a two-tiered analysis. After excluding multiple births (which can complicate an analysis like this one), they analyzed the full panel, 8,237 children from 4,071 families, using standard multiple regression models. They controlled for all of the things you would expect (age, race, mom’s marital status, region of the country, maternal education, family income, maternal employment status, insurance status, birth order, preterm birth, maternal smoking during pregnancy, maternal alcohol consumption during pregnancy, prenatal care initiation during first trimester). Their results indicated that breastfed children 4 to 14 did better on every outcome measured except for asthma. So in this part of the study, the benefits of breastfeeding appeared to be impressively wide-ranging. But remember: the potential for confounding was still present in this part of the study.

Next, they moved on to the heart of the study, in which they compared outcomes within families. In 665 of the families studied, siblings had different breastfeeding experiences. That is, one sibling was breastfed while another was not. When the authors investigated the 1,773 children from these families, the results changed. Big time. All of those outcome measures that looked better in breastfed kids in the first part of the study? They lost statistical significance. One interpretation of these results–the authors’ interpretation–is that when we are better able to control for factors like socioeconomic status and race, many of the apparent benefits of breastfeeding in the US disappear. They may not exist at all, or they may be too subtle to detect. If this information is correct, it is important to provide to mothers, as breastfeeding is often a very difficult process, especially for working women. If the benefits aren’t as large as advertised, some mothers may decide not to do it.

Some Potential Limitations

We already talked about the insidious role that residual confounding plays in population health studies. There is another big problem that we face when we study breastfeeding in large populations, though. And that problem is measuring breastfeeding. Getting good measures of breastfeeding for the huge number of kids in a population-based study like this one is next to impossible. These big studies are our primary source of large-scale breastfeeding data, but most of the time whether or not a woman is breastfeeding is just one box of many to be ticked off in a long survey. Breastfeeding is complicated, and these studies don’t do nuance. They’re just not designed that way. What if a mother only breastfeeds a baby in the hospital after delivery? Should we count that baby as breastfed? Is it fair to expect that the benefits associated with breastfeeding for a couple weeks are similar to those associated with breastfeeding for six months or more? Also, many babies are fed a mixture of breastmilk and formula. Typically, surveys don’t ask about this. So measuring the “exposure” being studied, breastfeeding, is really problematic. In this study, breastfeeding was coded as either “yes” (for any length of time) or “no.” However, information on the duration of breastfeeding was also collected (that is, how old the baby was when breastfeeding ceased entirely).

As EA Quinn has pointed out, one key feature of this study that is not described in the article is what “breastfeeding” means in the families in which one child was breastfed and another was not. What are we comparing? It seems as though it would be a little unusual for a woman to be super gung-ho about breastfeeding one kid while not breastfeeding another at all, barring health problems in mother or baby. For that reason, it’s natural to worry that maybe in this particular group, we’re comparing kids who were not breastfed to kids who were breastfed for only a very short time (maybe only days or weeks). If the kids in the intra-family comparison were only breastfed for a very short period relative to the kids in the larger sample, we would expect any beneficial effects of breastfeeding to be much attenuated, which could explain the results. In other words, it’s not that the results from the entire sample were wrong–it’s that the statistical power to detect those beneficial effects in the within-family comparison disappeared. For that reason, I asked Colen about the mean duration of breastfeeding in the within-family comparison. She acknowledged that the duration of breastfeeding WAS significantly shorter than in the full sample (in which the mean duration of breastfeeding was 23 weeks). However, when we talked she wasn’t sure what, exactly, that duration was. If I get that information, I’ll be happy to update the post for any interested readers.

Another important limitation is that these results are primarily relevant to mothers in the US. I think the authors did a fine job of making it clear that these results were relevant to US families. The media, not so much. It’s important to remember that the breastfeeding environment in the US is pretty unique. On the plus side, we have access to clean water, which makes formula-feeding a much safer alternative than it is in many low-income countries. On the minus side, pro-breastfeeding policies in the US are pretty terrible. Our family leave policies are awful, making it very hard for many women who want to breastfeed to do so. Workplace daycares are few and far between. There may be no space/time for women to pump at work. Therefore, this study was geared towards addressing an issue that is particularly problematic for mothers in the US: when breastfeeding is so damn hard, and may even endanger a woman’s livelihood, just how many resources should be devoted to it?

Why Keep Doing These Population Health Studies of Breastfeeding if They Are So Tough to Interpret?

Over at Mammals Suck, understandably frustrated guest poster Melanie Martin asked “What if we stopped looking for small statistical effects of breastfeeding on IQ, and put more of our money and effort into researching the unique and variable aspects of human milk composition and synthesis? What if we conducted clinical studies to determine if different ratios of breast milk intake, or different durations of breastfeeding, result in observable, biologically meaningful differences in metabolic, immune, and neurological function?”

I’m sympathetic. Trying to decipher what’s going on in the tangle of epidemiological studies of breastfeeding in high-income countries is an exercise in frustration. I agree with Martin that we need more information on the proximate effects of breastfeeding. However, I also think it’s incredibly important to keep studying distal outcomes like the ones examined in this study–even if it’s exceedingly difficult. Why? Because the path leading from proximate to distal health outcomes is a winding, confusing one. We need data for every step along the way. In public health, often what we expect to happen, based on what we know about proximal effects, does not actually happen. Consider, for example, the literature on vitamins and cancer. There are all sorts of reasons to suppose that taking vitamins and minerals could help prevent cancer. But big randomized controlled trials have shown us that they actually appear to raise cancer rates in at-risk groups. Now just to be clear, I’m not comparing breastfeeding to cancer! And I’m not predicting that someday, as a result of better studies, we will be shocked to find that breastfeeding is actually bad for kids. Not at all. But given the difficult choices that mothers in this country do have to make, I think it IS important to figure out how the effects of breastfeeding on metabolic, immune, and neurological function translate into actual health outcomes. I think this will be especially important if we want to use breastfeeding research to influence policy.

I truly believe we are making strides. For example, we now have results from randomized controlled trials of breastfeeding. In a trial in Belarus, breastfed babies were less likely to experience gastrointestinal illnesses and atopic eczema, but no reduction in respiratory tract infections was found. That’s valuable information! And George Davey Smith and colleagues have taken another creative approach to the problem of confounding in breastfeeding studies:  they investigated the effects of breastfeeding in two samples in which the structure of confounding differed. One sample was from the UK, where breastfeeding is associated with higher socioeconomic status. The other sample was from Brazil, where there is no association between family income and breastfeeding. After examining effects on blood pressure, body mass index, and IQ, they found that only the beneficial effect of breastfeeding on IQ was present in both samples. This, too, is valuable information! I think we have to be cognizant that no one study is going to give us all of the answers. But studies like these do provide the puzzle pieces we can begin to fit together to learn more about the benefits of breastfeeding.

My Take On The “Is Breast Truly Best?” Study

This study, like any population-based study, certainly has limitations. Based on the available data, it does seem possible that the lack of beneficial effects observed in the intra-family comparison may simply be due to a lack of statistical power. But I think the approach taken by Colen et al., in which siblings were compared to avoid confounding, is a good one. If we can find enough families in which one sibling is breastfed for significant periods of time and another is not, barring extraordinary circumstances like health problems, we can gather some interesting information. I’d be really interested in hearing what the mean duration of breastfeeding was in that intra-family comparison group.

The benefits of breastfeeding as measured in older children may be subtle. And the presence/absence and magnitude of different benefits is bound to be information that struggling new mothers will find valuable, so I believe these findings are worth following up on. As Colen et. al state, “Total commitment to 6 months of exclusive breastfeeding is a very high expectation of mothers, especially in an era when a majority of women work outside the home, often in jobs with little flexibility and limited maternity leave, and in a country that offers few family policies to support newborns or their mothers. The line between providing information about the benefits of breastfeeding and stigmatizing mothers facing structured, valid, and often difficult trade-offs in the care and financial support of their children or in fulfilling their own human potential must be drawn sensitively.”

So let’s push for more breastfeeding research. Let’s let funders know that instead of gathering vague breastfeeding information as an afterthought in big studies, it’s important to gather quality, detailed data. Yes, it will be expensive. But it’s important. This is a subject worth studying, and any good cohort will take years to follow. Let’s get started now!

 

Biosphere 2: Better than Fiction

biosphere2I have vague memories of learning about Biosphere 2–the huge, hermetically sealed bubble built in the middle of the Arizona desert–in school. I think there was some Scholastic-type newsletter about it, with a photo of all the Biospherians in their jumpsuits, and a rundown of all the ecosystems present in the big globe. Remember how much time kids in the 80s-early 90s spent learning about the rainforest? I’m pretty sure we must have learned about Biosphere 2 during the media blitz that accompanied the Biospherians’ entrance into their new home. And I’m sure what we read was totally optimistic, as coverage of current science for elementary school students usually is. But what happened after their big entrance? Were they really able to live totally sustainably for years in their big glass bubble? I had no idea.

Last week, when I came across a retro report on Biosphere 2 in the New York Times, it was like getting a forgotten part of my childhood back!  (For anybody who hasn’t seen it yet, the retro report series is awesome. And one of my favorite reporters, Michael Winerip, wrote this one up.) The retro report movie and the accompanying article were long on interest but short on detail.  Rumors of cults? Starvation? Oxygen shortages? A division among the Biospherians that erupted into physical violence? I wanted to know more! So I did some digging, and here is what I found.

The origins of Biosphere 2. Apparently the idea for Biosphere 2 was hatched on the Synergia Ranch, in New Mexico. The ranch was founded in 1969 by a guy named John Allen; it was an ecovillage/commune that counted some future Biospherians as members. The commune members, or Synergists, practiced organic farming, ate silently at mealtimes as they contemplated their food, and were part of an improv troupe called the Theater of All Possibilities. One Synergist, Texas oil billionaire Ed Bass, provided the funding for Biosphere 2 (~200 million from 1985–2007). Some people were discomfited when they learned about Mr. Allen’s vision, in which biospheres like this one would serve as refuges in an apocalyptic world laid to waste by nuclear war or some other disaster. So the PR people tended to focus on the neato science aspects of it. Ecology, rainforests and coral reefs, sustainability, etc. Originally, the biosphere was conceived of as a grand 100-year experiment. But it didn’t proceed exactly as planned.

Mission 1. The adventure began in September of 1991, when the 8 Biospherians (4 men and 4 women) sealed themselves in the bubble. The sphere, which covered an area the size of two and a half football fields, included a number of different ecosystems: a rainforest, an ocean with a coral reef, mangrove wetlands, a savannah grassland, a fog desert, an agricultural area, a human habitat, and a below-ground area that housed infrastructure. In all, 3,800 species of animals and plants were sealed inside, including hummingbirds, monkeys (!), and earthworms. Prior to the spherians’ entrance, two Native Americans in full dress and a Tibetan Buddhist monk participated in a sunrise prayer for their success.

The primary goal was to figure out whether the Biospherians could live totally sustainably for 2 years–with no food, air, or other supplies from the outside. Although the Biospherians were often called scientists in the media, only one, Roy Walford, was actually trained as a scientist. Walford was the crew’s physician, and his research interests focused on aging and diet. Apparently, inside the sphere, the residents soon broke into two factions: one group supported director John Allen and one questioned his methods. The anti group felt that the spherians should be formulating research hypotheses that would then be evaluated by the Science Advisory Committee. The pro-Allen faction, was against this idea. Apparently, despite the magnitude of this scientific endeavor, no regular scientific records were kept during the Mission! In February 1993, the 10-member scientific advisory team resigned. One of the remaining sources of scientific advice for the project was the mysterious Institute of Echotechnics. There were rumors that critics in the world of science were silenced by threats of lawsuits. However, a group of respected scientists wrote up a report on the project at the request of Ed Bass. Among other things, the report criticized the lack of a well-developed scientific plan, the project’s excessive secrecy, and possible “embellishments” of data. Walford later said, “Management thinks it knows more science than it does, but they don’t understand that in doing science you have to be asking a particular question, not just collecting a lot of random data. They have been [called] environmental zealots, and I think that’s true.”

930926_B2CrewAfterReentry_HM_UAThere were also allegations that the anti-Allen faction was punished with extra work and the withdrawal of privileges. Fights turned nasty–there was even spitting involved. It’s natural for a small group of people in trying circumstances to become short-tempered. But critics have pointed out that the way in which the spherians were chosen and prepared probably contributed to the level of dysfunction. Astronauts, for example, are carefully chosen for space missions. They must have stable psychological profiles, be very physically fit, and have extensive training in their fields. The Biospherians, by contrast, selected themselves. They were enthusiastic environmentalists and most of them were good friends, but they were not trained scientists (with the exception of Walford), they didn’t have any special training for their roles in the biosphere, they made decisions by consensus as questions came up rather than following a pre-established plan, and there was no real external scientific oversight. In other words, chaos may have been inevitable.

Fighting wasn’t the only thing that made life inside the sphere unpleasant. Oxygen levels dropped and carbon dioxide levels soared, making it very difficult to breathe. Later, researchers figured out that the concrete in the structure was absorbing oxygen, and the high organic matter in the soil also appears to have contributed to the oxygen/carbon dioxide problems. It got so bad that oxygen from outside had to be pumped in, and eventually a carbon dioxide scrubber was installed, which critics said voided the project’s raison d’etre (remember: nothing in or out, including air). In the end, all of the vertebrates except for the Biospherians and the pollinating insects died as a result of the wildly fluctuating carbon dioxide levels. Plus, the spherians had the bad luck of entering during an unusually cloudy time, which impaired the photosynthesis of the plants. Because the crops did not grow well, the Biospherians had very little to eat, and they lost weight — a lot of it. They had to resort to eating emergency food supplies, including seeds that were meant for planting. The coral reef dissolved into sludge. Cockroaches flourished, until they were eaten by an army of ants that seemed to appear out of nowhere. Although in the beginning there were domesticated animals, there wasn’t enough food to support them. The residents had to kill them. And one detail that especially interested the public and may have been difficult for the Biospherians to get used to: there was no toilet paper.

After the mission, a number of glaring mistakes were identified. When populating the various ecosystems with plants, species from all over the world were chosen and clumped together. Rather than resembling a natural ecosystem, in which different species have evolved to occupy different niches, brand new combinations of species were inadvertently being tried out. It did not work well, and  a few very successful species tended to crowd out the rest. The soil chosen was way too rich in organic matter, which contributed to the oxygen/carbon dioxide problems. And crops (like peanuts and soybeans) that depend on species-specific soil bacteria called rhizobia to grow didn’t get what they needed. These were all problems that agricultural specialists could have identified quickly. In fact, experts at the University of Arizona pointed out the problems with the rich organic soil, but they were ignored.

Eventually, the crew threw in the towel. The mission ended exactly two years after it started, in 1993. It’s pretty amazing they toughed it out for so long! I would have been banging on the air lock after a week.

Mission 2. The second mission lasted from March 1994–September 1994 and included 7 Biospherians. This time, having learned from the problems encountered during Mission 1, it was decided that spherians would rotate in and out in 180 day shifts and scientists and other personnel would be allowed to visit. By April of that year, some of the top managers of the project (including John Allen and Margaret Augustine) were replaced. Apparently Biosphere 2, which was originally conceived as a money-making venture, was requiring big infusions of cash and funder Ed Bass had had enough. A few days after Allen and Augustine were dismissed, two of the original Biospherians broke into the sphere, breaching the airlocks and deflating the system’s air pressurizer. They said their goal was to warn their comrades inside about the change in management. In the aftermath, a number of people connected to the Biosphere project accused John Allen of running a cult, including former Biosphere official Stephen Storm and the mother of Biospherian Abigail Alling. Among other things, they accused Allen of brainwashing and even physically abusing the Synergists who lived on his ranch.

Post-Biosphere Events. Eventually Ed Bass washed his hands of Biosphere 2.

First, Columbia University bought the facilities in 1995 and used them to conduct experiments. A lot of their work focused on manipulating carbon dioxide levels to simulate global warming.

Then, in 2oo7, the University of Arizona took over research at the sphere. It’s in their hands now. If you want to learn more about current research, you can visit their website. It seems like they are leveraging the unique blend of ecosystems to do some interesting ecology experiments.

I did a literature search to try and figure out what kind of scientific legacy this project left behind. It’s biggest contribution seems to have surrounded the hunger the biospherians were subjected to–a lot of great studies on calorie restriction came out of the work. As miserable as it must have been to be constantly hungry, the low-calorie, nutrient-rich diet that they ate contributed to pretty excellent health among the Biospherians. Their cholesterol, blood pressure, and glucose levels all fell. Perhaps Biosphere 2 should be rebranded as a health spa!

The early years of Biosphere 2 were a sort of fascinating debacle, but there may be many decades of research that lie ahead. Maybe it will end up lasting 100 years.

Want to go visit the Biosphere after reading all of this? You’re in luck. They give tours! And apparently they are pretty good–Trip Advisor reviewers gave them 4 out of 5 stars. Next time I’m in Arizona…

The Great Bitcoin Experiment

I learned about bitcoins in a great article by Joshua Davis in the New Yorker. Invented in 2009 by a mysterious figure going by the pseudonym Satoshi Nakamoto, bitcoins are a form of cybercurrency. They are given away (for free) in periodic lotteries; by 2040, 21 million bitcoins will have been released.

At first, as you can imagine, there wasn’t a lot of demand for bitcoins. I guess initially it was pretty easy to obtain bitcoins from the lotteries. Then interest started to grow. People dedicated computer systems to these lotteries, hoping to score a large number of bitcoins. These people are called “miners,” and it sounds like these days it is hard to get your hands on bitcoins via the lottery unless you are a miner. By 2010, the value of a bitcoin started to take off. Then, as you can see from this chart, wild fluctuations in value started. Those swings haven’t deterred everyone–it’s reported that the Winklevoss twins are holding onto over 11 million dollars worth of bitcoins, for example, and the attention this new form of currency is getting from the media seems to be growing weekly. Screen Shot 2013-05-11 at 3.00.13 PM

So what can you actually do with bitcoins? You can exchange them for dollars at one of the many exchanges that has popped up. One just started in Union Square–you can check it out on Mondays afternoons, starting about 4 PM. But simply hoarding bitcoins and occasionally exchanging them seems alittle boring. You can also use bitcoins to purchase drugs or other contraband in online forums like Silk Road, since bitcoins aren’t tied to your identity the way credit cards are and transactions are  untraceable. Not a drug user? For the more boring among us, there are some legit businesses that take bitcoins. WordPress, OkCupid, and Reddit accept them. And if you live in New York, you can settle your bartab at EVR with bitcoins. I’ve never tried Foodler (they don’t have many options in my neighborhood compared to seamless.com or GrubHub), but they take bitcoins. Evidently, one of the benefits of accepting bitcoins is that companies don’t have to pay credit card fees AND they don’t have to worry about charge-backs. Once a transaction is done, it’s done. Recently, Kashmir Hill, an intrepid Forbes reporter based in San Francisco, even tried to live on bitcoins for a week. Apparently it can be done, but it is a major pain.

This is a setup for a pretty fascinating experiment. To a lot of people, the idea of a currency not controlled by the Fed is pretty exciting. No one can decide to print more bitcoins when times are tough–the number released is capped, and they are released on a schedule in order to prevent inflation. As I noted earlier, you don’t have to deal with credit card companies when you are using bitcoins–and if you are traveling abroad, you don’t have to worry about currency conversion fees. Some of the drawbacks are that bitcoin exchanges could potentially act as money laundering havens, it’s still a rarity for a business to take bitcoins as payment, and there is no safety net in place if somebody else gets their hands on your bitcoins. You also have to trust that “Satoshi Nakamoto” is trustworthy and his scheme for bitcoin release will go exactly as planned. So how long will bitcoins be around? Is this a trend that will fizzle out in the near future? Or will bitcoins take off as an alternative form of currency? I’m really curious to see how this will turn out! I’m thinking about getting some on one of the exchanges just for fun… or maybe I will try to convert one of my old computers into a bitcoin mining operation and become a bitcoin millionaire.