The microbiome doesn't always explain everything.

Microbiome research is sexy. Just look at the Google Trends graph. Anyone and everyone is studying the gut, nasal, vaginal, skin, oral, aural, any-other-body-part microbiome. This means that a lot of research is getting published saying what constitutes a “healthy” vs. “unhealthy” microbiome (hint: it’s not binary or that simple)
So don’t blame me for the fact that I read this new study with a healthy bit of skepticism. In fact, I was pointed there by a press release that, in my opinion, overstated their conclusions.

The researchers found that prenatal maternal stress – as measured through a combination of surveys and circulating cortisol (a stress hormone) levels – predicted some aspects of the infant’s gut microbiota, such as the abundance of some microbial genera. Now, while they neglected to correct for the multiple tests that they conducted, they certainly found a significant amount of microbial genera that were associated with their variables of interest. They think that the causal pathway is that the mother’s cortisol levels alter the infant gut microbiota.

Mothers who reported high stress levels and presented high cortisol readings had babies with more Proteobacteria and fewer lactic acid bacteria and Actinobacteria in their microbiota. This represents a poor mix of microbiota,

But does it really represent a “poor mix of microbiota”? I think that is still up for some healthy debate.
They conclude with a rather strong statement of a possible intervention:

These results suggest that offspring health may be improved by modifying the intestinal microbiota during pregnancy, especially in women with stress.

And here’s the “CYA” clause end of the press release:

The researchers are keen to stress that the clear correlation they discovered should not be confused with a causal link.

Zijlmans MAC, Korpela K, Riksen-Walraven JM, de Vos WM & de Weerth C (2015) Maternal Prenatal Stress is Associated with the Infant Intestinal Microbiota. Psychoneuroendocrinology. doi:10.1016/j.psyneuen.2015.01.006

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