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.