Thursday, October 31, 2013
A miscarriage of science: BPA’s unproven pregnancy risk
The headlines are out: Pregnant woman should fear the chemical Bisphenol A (BPA) because a “new study” says it increase the risk of miscarriage. Fortunately, we have lots of good reasons to doubt these headlines.
What does the study really say? We don’t completely know since it’s not available in any peer-reviewed publication. All that’s available is an abstract produced for a recent presentation at a conference hosted by the American Society for Reproductive Medicine (ASRM). The abstract does, however, provide enough information to allay fears—despite how the headlines read.
Based on the abstract, we can see that the study examined 114 women in the early stages of pregnancy who also are a high-risk group for miscarriage. The researchers took “spot samples” of the women’s blood and measured BPA in their blood serum. Sixty-eight of these women suffered from miscarriages, and the rest carried their babies to term.
The researchers then measured the BPA in the serum to see if those who miscarried had more BPA in their blood serum than the others. They then divided these 68 women into four groups based on the BPA exposure levels, ranging from those with the lowest to those with the highest. Using this data, the researchers calculated that those in the group with the highest BPA levels in their serum had an 80 percent higher risk of miscarrying than did those in the lowest-exposed group.
Sounds pretty clear, right? WRONG! Here’s why this study isn’t as meaningful as you might think.
First, the authors did not find a cause-and-effect relationship, they simply found an association, and it was pretty weak. Researchers express the strength of such associations numerically as a “risk ratio.” In this study, the risk ratio for the highest risk group was 1.83, which is low and suggests that the result may have arisen by accident or researcher bias. “Although any measure of risk would follow a continuous distribution and there are no predefined values that separate ‘strong’ from ‘moderate’ or ‘weak’ associations, relative risks below 3 are considered moderate or weak,” points out Paolo Boffetta of the The Tisch Cancer Institute at Mount Sinai School of Medicine in an article on the topic of relative risk.
The study’s promoters are aware that the findings are inconclusive, yet they advance alarming claims with clever rhetoric. For example, Dr. Linda Giudice, president of the ASRM,commented to the press that although the study proves nothing, it adds to the “biological plausibility” that BPA affects fertility and health. It is true that if something also has a biological explanation (plausibility), researchers can make a stronger argument for a cause-and-effect relationship—particularly if their study discovers a reasonably strong association. But using biological plausibility to rationalize a weak association is itself, pretty weak!
Second, the sample size here is very small, which greatly increases the probability that the weak association is little more than accidental. Larger samples by definition are more representative of the larger population. Accordingly, if this study was ten- or twenty-times bigger, a weak association would have greater meaning.
Third, the BPA was measured only once. Since BPA levels in the body can fluctuate considerably over time, one-time measures can’t reveal which women really have higher exposures. Accordingly, the data going into the study is not good enough to draw conclusions.
Finally, while the authors and news organizations suggest this adds to the research indicting BPA, they fail to note that many other studies that contradict it. This study would be much stronger if it was consistent with the larger body of research, particularly the larger, best-designed scientific research. But it’s not.
Scientific panels around the world have reviewed the full body of BPA research repeatedly, and they all concluded that current consumer exposure to BPA is simply too low to have any adverse public health impacts!
This study is consistent with the almost daily barrage of government-funded, usually small and often poorly designed studies reporting largely meaningless weak associations. Politicians have funded them in response to the clamoring and hype created by misguided, anti-chemical environmental activists. We can expect to see more of this misuse of science as the researchers and their activist partners continue the fear-mongering.
This case is full of such examples. In a press release, referencing this unpublished study, Giudice notes: “Many studies on environmental contaminants’ impact on reproductive capacity have been focused on infertility patients and it is clear that high levels of exposure affect them negatively. These studies extend our observations to the general population and show that these chemicals are a cause for concern to all of us.”
This cryptic comment has no real relevance to the study at hand, even though Giudice placed it directly under the abstract in the release. After all, what chemicals is she talking about? Who knows? It is clear that the high-level chemical exposures to which she refers have nothing to do with extremely low, easily metabolized trace levels of BPA. Nothing at all. But her comment worked well in the “news” stories alleging BPA-induced miscarriage risk. And that’s the only apparent reason to make such a misplaced comment.
The authors have also spun the issue to grab headlines. Lead author, Ruth B. Lathi notes in USA Today, that although they did not show that BPA is dangerous “it’s far from reassuring that BPA is safe.” Well that comment may be safe to say since you can’t prove absolute safety—of anything! Not even a glass of water.
She also recommends avoiding plastic food packaging, not cooking in plastic food containers, and not leaving bottled water in the sun. Never mind that BPA is not used for most of these products, which Lathi doesn’t specify. There isn’t any BPA in the lightweight flexible plastic that makes single-use bottled water or plastic storage containers such as Gladware, which is what Lathi seems to be suggesting we avoid. She also says to limit eating canned food.
BPA is used to make hard-clear plastics, such as the 5-gallon water jugs used in office water coolers and safety goggles. And it’s used in resins that line canned goods to prevent rust and the development of deadly pathogens in our food supply. Can Lathi assure us that removing those resins will be safe? Certainly not, yet her rhetoric advances policy in that direction.
But what does it matter? After all, the scientific discussion about BPA apparently isn’t about the facts—or good science.
Pregnant women who gain a lot of weight may be more likely to have a child with autism
Some appropriate caution about the causal path expressed below
Pregnant women who put on a lot of weight may be more likely to have an autistic child. Weight gain in pregnancy varies greatly, with most women gaining between 17.5lb to 30lb, putting most of the weight on after week 20.
Now a study has found that autism spectrum disorder was more prevalent in in children born to mothers who gained 33.5lb during pregnancy than in those who gained 30.5lb, for instance.
Previous studies have identified links between pregnancy weight gain and autism. But this new study found a link between autism and pregnancy weight gain after taking into account how much a woman weighed before.
Lead author Dr Deborah Bilder, an assistant professor of psychiatry at the University of Utah, said: 'These findings suggest that weight gain during pregnancy is not the cause of autism.
'Rather, [it] may reflect an underlying process that it shares with autism spectrum disorders, such as abnormal hormone levels or inflammation.'
Researchers carried out the study by comparing the cases of eight-year-olds living in Salt Lake, Davis and Utah counties.
A group of 128 children diagnosed with autism spectrum disorders were compared to a control group of 10,920 children of the same age and gender.
The research was possible in Utah because it tracks how much weight women put on during pregnancy.
The study had one surprising result: Researchers found no connection between a mother’s BMI before she became pregnant and the incidence of autism - something that hasn't been seen in previous studies.
Researchers also examined a second group of 288 Utah children diagnosed with autism spectrum disorders and compared their data with that of unaffected siblings.
In both scenarios, pregnancy weight gain patterns obtained from birth certificate records were identified as common factors in mothers who gave birth to children born with autism.
The findings suggest that these small changes in pregnancy weight gain and autism may share the same underlying cause.
Dr Bilder added: 'The findings in this study are important because they provide clues to what may increase the risk of having an autism spectrum disorder.
'Doctors have known for a long time that proper nutrition is essential to a healthy pregnancy. Pregnant women should not change their diet based on these results. Rather, this study provides one more piece for the autism puzzle that researchers are exploring.'
The findings were published in the journal Pediatrics.
Posted by jonjayray at 12:30 AM