Made in China: POPs linked to birth defects?

A new study in the Proceedings of the National Academy of Sciences claims to link placental levels of various “persistent organic pollutants” (POPs) with neural tube defects (NTDs) in a population of rural Chinese.

But aside from the small study size (80 cases of NTDs), failure to rule out confounding risk factors for NTD, inconsistency of association among POPs, and the absence of credible studies linking POPs with NTDs despite generations of widespread exposures around the world, the error bars around the purported associations are simply wild.

If you check out Table 3 of the study, you’ll note that the margins of error surrounding the odds ratios are huge — i.e., 3 to 8 times larger than the magnitudes of association. When the margin of error is larger than its purported association, the association is inherently unreliable.

The overall results appear to be heavily skewed by the 4th quartile of POPs exposures (Fig. 1), which is more likely to be an indicator of poverty among these rural Chinese women. It’s easy to imagine that these “high exposure” women also had poor quality diets (e.g., inadequate folic acid intake is associated with NTDs). Although the researchers claim to have interviewed the women after delivery about their folic acid intake, no effort was made to actually verify responses.

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2 responses to “Made in China: POPs linked to birth defects?

  1. Ben of Houston

    An adjusted odds ratio with 95% confidence between 1.45 and 62.65? Between 3.27 and 120! All this from a group of 80 cases of neural tube defects? Are you kidding me?

    There were only 50 controls, and on average, they had lower concentrations of the tested pollutants, despite none of the changes being doublings. Finally, though there was a total of slightly fewer DDTs in the infected than the controls (60 vs 61), the relationship is calculated as the second strongest of the effects. This appears to be completely mathematical artifacts.

    Is this the best our National Academy can produce? No wonder Feynman quit.

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